Spring Grub Control Not Your Best Bet

Spring is almost upon us and overwintering white grubs will soon be emerging from the depths to continue feeding for a short time before they pupate. These overwintering grubs typically spend the frigid months of December – February deep in the soil profile (up to 12 inches deep) to avoid freezing. As soil temperatures begin to rise (like they have this month), these grubs “wake up” and work their way into the thatch/soil interface to continue feeding. By mid-April spring feeding is usually in full swing and it is sometimes accompanied by an increase in skunk and raccoon foraging activity that can occasionally damage the turf.

Although it may be tempting to try to manage white grubs during this time, data clearly indicates that the effectiveness of chemical applications targeting white grubs in Spring is greatly diminished. Unless serious secondary damage resulting from animal foraging activity is observed, attempts to manage grubs at this time should be discourage. The window of opportunity and likelihood of success are so small that applications made at this time will almost certainly be wasted.

If secondary damage from animal foraging is simply too much to tolerate, an application of trichlorfon (Dylox) is the only course of action that stands a chance of being effective, and even then the odds are not in your favor. Also, remember that killing white grubs present in April will likely have no impact on white grub populations occurring later this year (July-October).

Instead, consider raking out and re-seeding damaged areas and forget about trying to control these overwintered grubs.

Doug Richmond, Turfgrass Entomologist

Part III: Controlling broadleaf weeds in newly seeded areas

This turf tip is part of a three part series on spring seeding.

Most turfgrass herbicides are intended for use on established grasses. Thus, herbicide use on newly planted grasses should be very conservative. If possible, wait until the grass has gone through several mowings or a full growing season before using chemical weed control. However, as described in Part II of this turf tip (add part II link here) there are some postemergence broadleaf herbicides that are safer on newly seeded turf including Drive (quinclorac), Tenacity (mesotrione), SquareOne (quinclorac + carfentrazone), and Imprelis (aminocyclopyrachlor).

If weed competition is severe enough to warrant herbicide use, a good rule of thumb is to wait until a recently seeded lawn has been mown two to three times before using the three-way herbicides (2,4-D + dicamba + MCPP) or Q4 Plus (quinclorac + sulfentrazone + 2,4-D + dicamba), Onetime (quinclorac + MCPP + dicamba), or Solitare (quinclorac + sulfentrazone). See the label of the product you wish to use for complete directions.

Keep in mind that the best time to control weeds is in the fall. See our fall posting on broadleaf weed control for more information on fall application timings (http://www.agry.purdue.edu/turf/tips/2010/10182010_broadleafweeds.html ).

Just as with spring seeding dates, it is important that when turf is planted in the fall that new turf seedlings are mown 2-3 times before a fall postemergent herbicide application is made for broadleaf weeds or alternatively that a herbicide is used that is typically very safe on new seedling such as Drive (quinclorac), Tenacity (mesotrione), SquareOne (quinclorac + carfentrazone), or Imprelis (aminocyclopyrachlor).

Aaron Patton, Assistant Professor/Turfgrass Extension Specialist

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Melting Snow Reveals Tiny Trails

With the winter snows finally melting away many are often surprised to find a series of tiny trails on the surface of their lawns and turfgrass fields. These are vole highways.

Voles are often called meadow or field mice. While they are similar to a house mouse in general size and shape, they have some important differences. Voles have small eyes and ears, stocky bodies and short tails when compared to other mice, but even more important is that they very seldom invade homes. Rather, they prefer to live in grassy fields or landscape beds.

Voles are herbivores. They eat seeds as well as leaves and stems of grasses and sometimes other green vegetation and occasionally, roots and bulbs. Often voles are attracted to, and take up residence under bird feeders where the seed is scattered and litters the ground. Removing or limiting this food source will, in turn, limit the voles in that area. Some have found that moving the bird feeders to areas that are less susceptible to vole damage is the preferred approach.

Voles do not hibernate during the winter months. They are active even during the winter and when snow is on the ground. They seem perfectly happy and actually do very well under the protection of the snow cover chewing away on the turfgrass plants. When the snow retreats what is left is a series of surface runways through turf areas. These measure about 2 inches wide and sometimes many feet in length. Fortunately, although these runs are an eye-sore now, they do not significantly damage the turfgrass. With the spring growth, these paths will fill in and the voles will soon be forgotten.

Even more damaging than the trails that they make in turfgrass, however, is the potential injury they may wreak on other plants. Voles can seriously injure trees, shrubs (and sometimes plastic irrigation lines) when they gnaw on them. And gnawing is what rodents do best! Rodents, including voles, seem to gnaw on everything, either for food or for fun. If given enough time to gnaw on the base of a tree, voles may completely girdle it, which will kill even a large tree.

When controls are required it is important to remember that voles are a major food source of many vertebrates including birds of prey. Their main protection from these predators is snow or dense vegetative cover. While we have little control over snow, an effective way to manage voles is to reduce their vegetative cover. Mow tall grasses in the fall so that they do not fall over and create vole habitat during the winter. Trim trees and shrubs including low lying plantings plants such as arborvitae, yews, junipers such that they are up off the ground. When possible, use rock mulch rather than bark mulch in the flower gardens and beds because this is much less favorable to voles. Mouse snap traps, baited with peanut butter and placed in the vole run, also can be used to control small, pesky, populations. When major infestations have to be controlled immediately, rodenticides may also be effective. Extreme caution must be exercised when employing them. These are mostly formulated as baits to be placed into burrow openings. Remember that other animals (including dogs and cats) dig for and prey on voles and will become exposed to baits if not used sparingly and properly. Always consult state regulations and use all pesticides strictly in accordance with label restrictions. Happy trails !!!

Tim Gibb, Turfgrass Entomologist
Judy Loven, Vertebrate Control Specialist

Cool-Season Turf Winterkill: Potential Losses and a Pathway to Recovery

This winter has been cold and long. From December 2013 through February 2014, Indiana had it’s 9th coldest winter on record and its coldest since 1979, 1978 was coldest on record (Fig. 1). With such cold temperatures, many are worried about winterkill.

Fig. 1. In the past 120 years, this was the 9th coldest winter in Indiana’s history.

Winterkill is a catch-all term that is used to describe the loss of turf over the winter months from various causes. Turf may succumb to winter from many factors including; direct low temperatures, desiccation, ice accumulation, crown hydration, traffic and disease. While cool-season grasses are general well-adapted to “cool” temperatures, including those occurring over winter, winterkill still happens under certain conditions. Further, some species are more tolerant of low temperatures than others (Table 1).

Table 1. Low-temperature tolerance of cool-season grasses. Adapted from Beard, 1973 and Fry and Huang, 2004.
Low-temperature tolerance	Turfgrass species
Excellent	Roughstalk bluegrass
	Creeping bentgrass
Good	Kentucky bluegrass
	Colonial bentgrass
	Creeping red fescue
Medium	Tall fescue
	Annual bluegrass
Poor	Perennial ryegrass
Very poor	Annual ryegrass

Causes of Winterkill

Low temperature

Turfgrasses prepare for winter by undergoing a process called “cold acclimation” in which certain sugars and proteins accumulate, cell walls become more fluid, and plant cells dehydrate. All of these changes help the plant tolerate low temperatures and prevent ice accumulation inside the plant cell, which may result in the cells rupturing.

Crown (the growing point) survival is critical to  a plant’s winter survival. Located at or just below the soil surface, the crown is normally insulated by the soil. Since soil temperatures fluctuate less than air temperatures direct contact with the soil helps winter survival. This is also one reason it is recommended that closely mowed areas are topdressed just prior to winter.

Despite the plant’s best effort to protect itself from low temperatures through acclimation, plant tissues can still die. When freezing or thawing occurs quickly, damage may increase. Additionally, the freeze/thaw cycle can impact winter survival with more frequent freeze/thaw cycles being more stressful to the plant.

 

Desiccation

Desiccation is death from drying during winter – winter drought. Desiccation is usually greatest in areas where the soil was dry going into winter or where there was little snow cover or precipitation during winter. This is more common in the drier states like Kansas, Nebraska and the Dakotas. Turf death due to desiccation in Indiana is rare.

 

Ice accumulation

Ice accumulation can kill turf. When annual bluegrass (Poa annua) is covered by ice for 45 to 90 days or creeping bentgrass is covered by ice for 90 to 120 days, death can occur. Often death occurs because the ice prevents gas exchange which limits oxygen and increases carbon dioxide to toxic levels.

 

Crown hydration

Crown hydration is the phenomenon by which deacclimating plant cells in the crown tissue of the turf can be damaged by ice crystallization causing plant cells to rupture and plants to die. This phenomenon is most common for annual bluegrass as it is quicker to break winter dormancy and begin taking up water than species like creeping bentgrass. The most common time for this phenomenon to occur is in late winter and early spring, during or after snow melt and during periods of rainfall followed by freeze/thaw cycles.

 

Disease

Snow mold diseases commonly damage turf during the winter months. Typhula snow molds (gray snow mold and speckled snow mold) and/or pink snow mold are problematic throughout the Midwest. For more information on these diseases, see our recent post at http://purdueturftips.blogspot.com/2014/03/snow-molds-in-winter-of-2015-14.html

 

Areas Prone to Winterkill

For the reasons discussed above and further addressed below, the following areas are more prone to winterkill.

• Turf planted with species that have poor or very poor low-temperature tolerance
• Immature seedling turf planted in late fall – especially tall fescue, annual ryegrass and perennial ryegrass
• Low spots with poor drainage
• Close mown turf – fewer carbohydrates
• Exposed areas prone to desiccation – not as problematic in Indiana as farther west
• Turf covered in ice for more than 45 days – especially annual bluegrass
• Areas trafficked during winter
• Malnourished turf – inadequate nitrogen fertilization or low soil potassium
• Shaded turf
• Species prone to pink snow mold like annual bluegrass and creeping bentgrass

How to Assess the Potential Damage

If you think your turf might be damaged, use a cup-cutter or spade on thawed turf areas or a drill and a hole saw on frozen areas to remove a plug from the area in question. Take several samples from both probable damaged areas as well as areas that you think are undamaged. Clearly label which plugs are which and then place them in a sunny window or in a well-lit are under a lamp. Keep them watered and watch for recovery.

Hopefully, spring will arrive soon and warmer temperatures should allow for the field examination of new growth and a better overall assessment of potential damage.

 

Level of Damage Reported in Indiana

Aside from some visible snow mold damage in areas where the snow has melted, the most likely damage we will see this winter will be from ice accumulations on annual bluegrass turf. We don’t anticipate much direct, low-temperature winterkill because much of the turf was insulated during our coldest temperatures. Superintendents whom we have corresponded with have sampled their turf and reported good green-up of ice covered turf (Fig. 2).

Please contact us if you are seeing significant turf injury due to potential ice accumulation or low temperatures.

Fig. 2. Left plug taken on March 17, 2014, right plug from same area March 11, 2014 and then grown indoors for one week. This diagnostic test shows the recovery and green-up of turf. Photo taken on March 17, 2014, courtesy Ryan Cummings, Superintendent Elcona CC, Bristol, IN.

Recovery of Lawn & Athletic Turf

In higher mowed turf like lawns or athletic turf we don’t anticipate much winterkill, except where areas received traffic. There may be more snow mold on areas were snow was piled next to streets and driveways or where snow drifted and accumulated. These piles should melt but in some areas, they may need to be removed to help the turf recover and begin to grow once temperatures moderate. A light raking of areas matted from snow accumulation or from snow mold will speed turf recovery and green-up.

If areas are predominately Kentucky bluegrass and you experienced some damage from snow molds, mechanical damage (such as a snow plow that went out-of-bounds), or even some loss of perennial ryegrass, one option is simply to do nothing and allow the Kentucky bluegrass to recover these areas through its spreading (rhizomatous) growth habit.

If a spring seeding is necessary to repair damaged areas, consider doing it before the ground completely thaws from winter. Although it is not necessary to seed before the ground thaws it may make seeding easier as soils are often soft and moist in the spring which may make it more difficult to seed certain areas, especially with heavier equipment. When seeding small areas, prep the soil by scratching the surface with a rake to increase seed to soil contact. Larger areas can be seeded with a slit seeder or aerification followed by seeding although it will be difficult to get equipment out onto the turf until temperatures warm and the soil dries.

Seed planted now will lie dormant until the soil temperatures warm in April. Spring seedings are more successful with tall fescue and perennial ryegrass than with Kentucky bluegrass. This is due to the faster germination rate and better seedling vigor of perennial ryegrass and tall fescue compared to Kentucky bluegrass.

If Kentucky bluegrass is seeded in the spring consider using a mixture of turf-type tall fescue: Kentucky bluegrass (90:10, weight: weight) or a mixture of Kentucky bluegrass:perennial ryegrass (such as 80:20, weight: weight)(Table 2). Seeding Kentucky bluegrass alone in the spring will result in marginal bluegrass establishment due to the slow germination and seedling vigor and increased competition from crabgrass.

 Table 2. Recommended seeding rates for lawns in Indiana.

Species	Seeding rate lbs/1,000 ft2	Days to germinate
Kentucky bluegrass	1.0 to 2.0	10-21
Kentucky bluegrass (80-90%) + perennial ryegrass (10-20%)	3.0 to 6.0	5-21
Tall fescue	8.0 to 10.0	6 to 10
Tall fescue (90%) + Kentucky bluegrass (10%)	5.0 to 7.0	6 to 21

Ideally a soil test should be conducted prior to planting any seed to determine phosphorus levels. Where a soil test shows deficiency and to help the seedlings establish, apply a “starter fertilizer” after emergence to enhance seedling development. Starter fertilizer is high in phosphorus (P) which is listed as the second number in the analysis on the fertilizer bag. For instance, a 16-22-8 fertilizer contains 22% P₂O₅. Apply the fertilizer according to the label directions would should supply at least 1.0 lb. P₂O₅ /1000 ft². This application will likely include nitrogen (first number in the fertilizer analysis), which will also help the seedlings develop an extensive fibrous root system that is better able to take up nutrients and obtain water.

Early spring preemergence herbicides are often necessary in Indiana to prevent troublesome summer annual grassy weeds such as crabgrass and goosegrass. Keep in mind that all preemergence herbicides (except Tupersan) work to prevent the emergence of turfgrass seeds as well as weed seeds, so do not reseed areas treated with a preemergence herbicide this spring or do not apply a preemergence herbicide if you plan on seeding.

If you need to reseed an area that it likely to have crabgrass, there are some different approaches that you can take to manage crabgrass in spring seeding.

• Tupersan (siduron) may be used for preemergence control of annual grassy weeds in newly seeded cool-season turf.  Check the label for rates and use directions. This herbicide is more expensive and short-lived, but it is the only safe preemergence herbicide to apply at the time of seeding. Tenacity and Pylex are postemergence herbicides with preemergence activity that are also safe to apply at the time of seeding fine fescue, Kentucky bluegrass, perennial ryegrass, and tall fescue.
• Another strategy is to use a postemergence herbicide in late May and June that is safe to use on seedling turf instead of a preemergence herbicide to control crabgrass. Options include Drive (quinclorac), Tenacity (mesotrione), Pylex (topramezone) and SquareOne (quinclorac + carfentrazone). These products can be most safely used very soon after seeding to control crabgrass (see label for exact details on each turf species). If the seedlings are more mature (mown 2-3 times following their emergence) then other products such as Q4 Plus (quinclorac + sulfentrazone + 2,4-D + dicamba), Onetime (quinclorac + MCPP + dicamba), or Solitare (quinclorac + sulfentrazone) can also be used. For homeowners, there are now several products that contain quinclorac which can be used. Look for quinclorac in the list of ingredients on the label. An advantage of this strategy is that most of these products will also provide good postemergence broadleaf weed control.
• A third option is to use Dimension (dithiopyr) in late May after a spring seeding to control newly germinated crabgrass that has emerged and is still at the 1-4 leaf stage prior to tillering. Dimension is the only preemergence herbicide which has good postemergence activity on newly germinated crabgrass. This application would also prevent future crabgrass germination through the rest of the summer in newly seeded areas. The assumption in this scenario is that the seedlings were planted in early spring and that they have developed enough of a root system to tolerate an application of a preemergence herbicide in late May.

Recovery of Putting Green Turf

If your putting greens were predominantly annual bluegrass and you would like the composition to remain so, then scratching/scarifying the surface to allow annual bluegrass to germinate in these thin areas is the best approach.

Most golf course superintendents will want to try and repair damaged areas with creeping bentgrass. Doing so can be difficult as bentgrass seedlings are not very competitive, traffic tolerant, or quick to germinate during cool-springs. The best approach to getting creeping bentgrass to establish is to:

• Prep the seedbed using solid tine aerification, core aerification, verticutting, spiking, or using other aerification attachments such as the Job-Saver to increase the potential for seed-to-soil contact. Use an improved cultivar of creeping bentgrass. See the article “Evaluation of Putting Green Bentgrass Cultivars and Blends” in our 2011 Purdue research report for more information.
• Light applications of soluble nitrogen (like urea) at 0.1 to 0.4 lbs N/1000 ft² every 7-21 days following seedling emergence should help putting green recovery and seedling establishment.
• Apply fungicides as needed to prevent additional spring diseases such as brown ring patch, Microdochium patch, and yellow patch.

Looking to the Future: How to Enhance Winter Survival and Minimize Future Losses

The most important factor in minimizing future winterkill is to plant low temperature tolerant turfgrasses. For example, a weed control program designed to reduce annual bluegrass in putting greens and increase creeping bentgrass will reduce the likelihood of future winter injury (NOTE: At Purdue, we are initiating a 2-year, USGA-funded experiment on annual bluegrass control in putting greens in April 2014).

While there are differences in percent winterkill among perennial ryegrass cultivars in northern research locations (http://ntep.org/data/pr04/pr04_10-11f/pr0410ft26.txt), a better approach would be to use a more winter hardy species like Kentucky bluegrass.
Physically remove ice (it’s hard work) from areas of high economic importance like golf course putting greens (Figs. 3 and 4).

Fig. 3. Photo taken on a putting green during the ice removal process after about 60 days of ice encasement. Photo courtesy Ryan Cummings, Superintendent Elcona CC, Bristol, IN.

Fig. 4. Removal of snow and ice to about an inch of snow depth (top) and then after two days of thawing weather in beginning of March (bottom). Photo courtesy Ryan Cummings, Superintendent Elcona CC, Bristol, IN.

Another approach to help remove ice accumulation is to topdress the ice with dark colored material such as milorganite (6-2-0), sunflower seeds, dark-colored or black sands, or other materials which will help increase heat absorbance and subsequently help to melt the ice.

Current research at Michigan State Some research is evaluating safer ice melt materials for their potential use as well. See this link for more information: http://www.msuturf.blogspot.com/2014/02/melting-ice-sheets-on-greens.html
 
Ensure that turf is receiving adequate nitrogen fertilization in the autumn months prior to winter. Nitrogen fertilization in autumn will help the plant produce valuable carbohydrates needed for overwintering and spring regrowth.

Improve drainage to reduce winterkill potential. Improving drainage (including opening up drain covers to allow draining during melting) will reduce ice formation (and depth) following thaws or mixed precipitation in winter.

There are mixed reports about the influence of potassium (K) fertilization on the winter survival of turfgrasses as some experiments have found potassium fertilization improved winter hardiness and others found no improvement in winter hardiness following potassium fertilization. Our recommendations are to use soil tests to determine if you need to make supplemental potassium applications. If your soil already has adequate levels of potassium, then it is not likely that additional potassium fertilization will improve winter hardiness.

Remove traffic from high value areas during winter as the turf can be damaged from traffic when the soil is frozen or when there is frost on leaf and stem tissues.

Both pink and gray snow mold can damage turf during winter. Some species are particularly susceptible to pink snow mold such as annual bluegrass and creeping bentgrass while gray snow mold causes similar levels of damage across turf species. Fungicides can be effective in preventing/reducing damage. More detailed information about snow mold diseases is presented at the following links.
http://www.extension.purdue.edu/extmedia/BP/BP-101-W.pdf (gray snow mold) http://www.extension.purdue.edu/extmedia/BP/BP-102-W.pdf (pink snow mold)

Shaded turf grows less vigorously during the growing season and often has fewer stored carbohydrates prior to the onset of winter. Additionally, shaded areas have cooler soils and are slower to warm/thaw following winter and are more likely to retain snow cover. As such, reducing shade on turf species that have poor low temperature tolerance is another strategy to increase winter survival. This includes removal of tree leaves in autumn shortly after they fall to encourage turf photosynthesis and carbohydrate storage.

 

Conclusion

Many factors have the potential to contribute to winterkill. Some of these factors are outside of our control and are dependent strictly on weather while other factors can be manipulated through sound cultural management to reduce potential for winterkill. Through sound turf management we can reduce the risk of winterkill but we can’t reduce the risk of winter. Spring will come eventually!

Aaron Patton and Cale Bigelow, Purdue Turf Program

 

References

• Beard, J.B. 1973. Turfgrass: Science and Culture. Englewood Cliffs, NJ. Prentice Hall.
• Fry, J. and B. Huang. 2004. Applied Turfgrass Science and Physiology. Hoboken, NJ: J. Wiley.
• Beard, J.B. 1964. Effects of ice, snow and water covers on Kentucky bluegrass, annual bluegrass and creeping bentgrass. Crop Science 4:638-640.
• Stier, J. C., and S.-z. Fei. 2008. Cold-stress physiology and management of turfgrasses. In Pessarakli, Mohammad (ed.) Handbook of Turfgrass Management and Physiology. Boca Raton, Florida: CRC Press.
• Tompkins, D.K., J.B. Ross, and D. L. Moroz. 2004. Effect of ice cover on annual bluegrass and creeping bentgrass putting greens. Crop Science 44:2175-2179.

Weed of the Month for March 2013 is Large Crabgrass

Large Crabgrass 

Biology: Large crabgrass ( Digitaria sanguinalis ), smooth crabgrass (Digitaria ischaemum), and to a lesser extent southern crabgrass (Digitaria ciliaris) are all species found in the Midwest that are collectively referred to as crabgrass. Large crabgrass is probably the most common of these in Indiana lawns. Combined, these crabgrass species are often considered to be the most problematic weed in lawns. Large crabgrass is summer annual grass that typically germinates in April in the Midwest (late March in southern areas and late April in northern areas). A germination tracker at www.gddtracker.net can be used to track the germination of crabgrass.

Identification: Large crabgrass is one of the first summer annual grasses to germinate in Indiana. Look for it first in bare soil areas like a garden or very thin turf areas and in areas with south facing slopes. First germination has occurred between March 22 and April 20 in the Lafayette area the past several years. Initial seedlings have an almost oval shaped, cotyledon. 

After the first leaf emerges, plants may remain small for several weeks if the temperatures are cool. Additionally leaves will develop and eventual plants will begin tillering in June. If you look close at large crabgrass (also sometimes called hairy crabgrass) you will see hairs on the leaves (blade and sheath) and a membranous ligule. If the leaf sheath and upper leaf blade are mostly smooth (hairless) then you likely have smooth crabgrass.  

As the plants mature they tiller and form small clumps. Large crabgrass also can produce stolons and root although it doesn’t spread far and remains mostly bunch type in growth habit.

Cultural control: Proper mowing (higher mowing heights), proper fertilization (some rather than none to improve turf density), irrigation to prevent summer dormancy during drought, and aerification of compacted areas to improve turf health are all cultural practices that can be used to reduce crabgrass.

Biological control: Some organic herbicides are available. The predominant organic herbicide in turfgrass systems is corn gluten meal for preemergence crabgrass control. This product has shown to be effective in northern states in lawns, although tests in Indiana and states south of Indiana show it has limited efficacy on crabgrass and that encouraging a dense turf through proper mowing, irrigation, and fertilization is equally effective.

Chemical control: Crabgrass can be controlled using preemergence or postemergence products.

Dithiopyr (Dimension), pendimethalin (Pendulum), and prodiamine (Barricade) are common ingredients in preemergence crabgrass products. These herbicides inhibit cell division and prevent crabgrass seeds from properly emerging. Since these herbicides work on germinating seeds, you must apply them prior to germination — with the exception of dithiopyr, which controls crabgrass after germination until it reaches one tiller.

Another approach to controlling crabgrass is to use postemergence herbicides after crabgrass has already emerged. Dithiopyr, quinclorac (Drive and others), MSMA (sod and golf), mesotrione (Tenacity), Fenoxaprop (Acclaim Extra) and other herbicides containing these ingredients can be used for postemergence crabgrass control. Each of these ingredients offers a slightly different spectrum of activity and works on specific sizes of crabgrass. Pick one based on the size of crabgrass you're treating and the other weeds you have present in the area.

For more information on weed control, search this blog (search box in upper left corner of page) and archived turf tip postings and check out our Turfgrass Weed Control for Professionals Publication.

Aaron Patton, Turfgrass Extension Specialist

Crabgrass is Now Germinating at Most Indiana Locations

The GDD Tracker website (sponsored by the MRTF and Purdue University) is predicting that crabgrass is now germinating at most Indiana Locations (see figure below). The GDD Tracker estimated that crabgrass germinated in Lafayette, IN after Wednesday this week and I was able to confirm this by identifying newly germinated crabgrass (see figure below) both in Lafayette and West Lafayette.

For those of you that have not yet applied a preemergence herbicide (crabgrass preventer), it is still possible to control crabgrass if you choose a product that contains dithiopyr – the only preemergence crabgrass herbicide that also has some early postemergence activity on crabgrass.

The weather is now changing. We will continue to monitor the growing conditions and provide updates as needed on turf growth and turf pests in 2012.

Turf Notes: Disease and Fungicide Update

Early Season Dollar Spot Sprays

The pathogen must be active in order for the mycelium to absorb a fungicide.  We know that Sclerotinia homoeocarpa grows when temperatures remain above 55F in the presence of ample moisture.  If such conditions prevail in March (as they did in 2012), then early season sprays may help reduce dollar spot severity later in the season.  If temperature and moisture conditions do not favor pathogen growth (as they did in 2010 and 2011), then the March application will have no effect.

Snow Molds

Winter conditions in the lower Midwest have been quite favorable for pink snow mold (aka Microdochium blight).  Springtime outbreaks on putting greens may require application of a remedial spray to limit disease spread, especially on sites with a history of the disease.  Often, a single application of a tank mix that includes chlorothalonil, iprodione, and a DMI fungicide will be effective in suppressing existing infections and limiting spread.

Our research with springtime fungicides on bentgrass fairways has had mixed results.  In most cases, fungicides applied to fairway height bentgrass after the outbreak is evident, did not hasten turf recovery.  If you are inclined to try a “fairway clean-up” spray, do a simple experiment by setting out a check plot—where an area of the turf remains untreated.  By comparing the check plot with the fungicide-treated areas, you will be able to evaluate the benefit of your fungicide spray.

Fungicide Notes:  Secure (fluazinam)

Throughout the season, I will try to make a point of discussing new and/or interesting fungicides for turf disease control.  The first is Secure (Syngenta) -- its active ingredient (fluazinam) was developed for crop disease control in the mid-1990s –but it is brand new to turf markets.  Secure is a contact fungicide with a reportedly multi-site mode of action.  Therefore, the risk of resistance is very low (although there is a report of resistance among populations of the Botrytis pathogen on rice).  The major target turf disease is dollar spot, although there may be some efficacy against other diseases.  Fluazinam’s multi-site inhibitor makes it very attractive as a component in fungicide programs that must deal with season-long dollar spot threats—especially where chlorothalonil limits are at issue.

Rick Latin, Department of Botany and Plant Pathology, Purdue University

 

A Much Different Start to the Year

A year ago we had record high temperatures and we were scrambling to apply preemergence herbicides for crabgrass control. On March 22 last year, I had crabgrass germinating in my garden! However, this year I can tell you that crabgrass is a long ways off from germinating today. The chart below shows the dramatic difference between 2012 and 2013, especially starting on March 7. I’ll continue to keep you updated as we progress this year on how the weather impacts our turf management.

Dr. Aaron Patton, Turfgrass Extension Specialist

Use Growing Degree Days to Better Time Your Applications

Monitoring growing degree days can be an effective way to better time applications and increase your weed control. A helpful website (www.gddtracker.net) is available to help you monitor growing degree days for timing herbicide and plant growth regulator applications. What can this website help me with?

1. Need help determining when to apply your preemergence herbicide? Visit www.gddtracker.net
2. Need help estimating when crabgrass is going to germinate in your area? Visit www.gddtracker.net
3. Should I use an amine or an ester this spring to control broadleaf weeds? Visit www.gddtracker.net (I’ll also cover this more on tips in the upcoming weeks).
4. When should I apply Embark or Proxy/Primo to my putting greens to regulate annual bluegrass seedheads? Visit www.gddtracker.net

What is a Growing Degree Day (GDD)? A growing degree day (GDD) is a method to track the heat units that have accumulated and are needed for plant growth and development. The formula for calculating GDD is:
GDD = ((max temperature °F + min temperature °F) ÷ 2) - base temperature °F, where the base temperature is normally either 22, 32 or 50 °F but varies based on the model.

For example, if the high today was 74°F and the low was 52°F and we used a base temperature of 50°F, our calculation would be, GDD= ((74°F + 52°F) ÷ 2) - 50°F = 13

In another example on a cooler day you might have a high of 58°F and a low of 40°F and with a base temperature of 50°F, our calculation would be, GDD= ((58°F + 40°F) ÷ 2) - 50°F = -1. When a GDD calculates to <0, we simply make it a zero and determine that no growth (or plant development) occurred on that day.

Models that help us predict plant development use accumulated GDD which is simply adding the GDD calculated each day and determining how many GDD units have accumulated thus far.
In some cases accumulated GDD can be used to monitor when weeds might germinate or flower or when grasses might produce a seedhead while In other cases accumulated GDD can be used to help optimize application timing such as with preemergence crabgrass applications or the selection of amines or esters for spring broadleaf applications. Research into plant development and optimal herbicide application timing has determined a window of accumulated GDD needed to best predict when to time these applications or when these events might occur.

While it is possible to track your own GDD using a local weather station, an easier way to do this is to use an online tool. The Purdue University Turf Science Program and the Midwest Regional Turf Foundation help provide financial support of Michigan State University Extension’s GDD Tracker, www.gddtracker.net. This website tracks GDD for the Midwest and provides updates for golf courses on timing annual bluegrass seedhead suppression applications, updates for all in the turf industry on crabgrass germination and preemergence herbicide application timing, and updates on broadleaf flowering and the timing of amines and esters for spring broadleaf applications.

Watch a video from Dr. Ron Calhoun (creator of www.gddtracker.net) to learn how to use this website.

Dr. Aaron Patton, Turfgrass Extension Specialist

New Weed of the Month Series: February is Prostrate Knotweed

This post kicks off a new series that we will be posting via turf tips called, “Weed of the Month”. In each post we’ll discuss a timely weed (one that you’re seeing at that particular time of year) and we will highlight its biology, identification, and control.

 

February's weed of the month is Prostrate Knotweed 

Biology: Prostrate knotweed (Polygonum aviculare) is an early germinating summer annual broadleaf that is often found in low-oxygen soils, including compacted areas next to sidewalks and previously flooded areas. Germination starts in late February and early March in many Midwest states.

Identification: Prostrate knot weed is the earlier summer annual weed to germinate in Indiana. Look for it first next to driveways and sidewalks. First germination has been in late-February or the first week of March the past three years in Indiana. Initial germinating weeds have a red hypocotyl. 

The seed leaves (cotyledons) are very narrow and it almost appears to be a germinating grass upon first inspection. 

As the plants mature they become tough, wiry, and prostrate in growth. This plant develops a thin taproot. It can be distinguished from prostrate spurge which exudes a milky white sap when it's stem is broken.

Cultural control: Reduce soil compaction through aerification and improve drainage in areas prone to flooding.

Biological control: None known.

Chemical control: 2,4-D by itself will provide only fair control of prostrate knotweed, but when combined with triclopyr (Turflon Ester Ultra or Triclopyr 4) or dicamba (Banvel, Vanquish), it should provide excellent control in cool-season turf. There are many combination products that contain 2,4-D and dicamba, including Trimec 992 and SpeedZone. Combination products that contain 2,4-D and triclopyr include 4-Speed XT, Chaser, Chaser 2 Amine, Momentum FX2, Turflon II amine, and TZONE.

In warm-season turf, metsulfuron (Manor, Mansion, MSM) or the herbicides listed above will provide effective postemergence control of prostrate knotweed.

Preemergence control of prostrate knotweed can be achieved with late fall (November or December) applications of isoxaben (Gallery, Isoxaben 75WG). Other preemergence herbicides will also work, but are less effective than isoxaben. You can apply isoxaben in late winter, but spraying conditions are not typically favorable at that time of year and it is difficult to predict exactly when prostrate knotweed might germinate although it is usually in early March.

Aaron Patton, Turfgrass Extension Specialist

 

New Turf Publication: Facts About Phosphorus and Lawns

A new turf publication has been posted on the Turf website:

Facts About Phosphorus and Lawns - AY-334
http://www.agry.purdue.edu/turf/pubs/AY-334-W.pdf

When Will Crabgrass Germinate?

With the rapidly warming weather, several are asking “When will crabgrass germinate?” The reason this is so important is because preemergence herbicides used for the control of crabgrass must be applied prior to emergence (except dithiopyr (Dimension) which can be used postemergence on crabgrass up to 1-tiller). There are several different ways to try and anticipate when crabgrass might germinate. My favorite is the GDD Tracker website. This blog post is an expansion of a post in 2011 with more information and sources.

Soil Temperature: Research says that crabgrass begins to germinate when the average daily soil temperatures reach 57 to 64 °F at a one-inch depth although large quantities of crabgrass seedlings will not start germinating until soil temperatures increase to 73 °F or above at a one-inch depth (Fidanza et al., 1996). Soil growing degree days (in contrast to the air temperature model highlighted below) have also been sued by others to predict large crabgrass emergence (Myers et al., 2004). The problem with using soil temperatures to predict germination is that most turf managers do not have access to daily soil temperature averages or are not collecting data with their own stations for their location. Going outside and collecting a soil temperature measurement with a thermometer provides only an instantaneous measurement and not an average over time.

Air Temperature Using Growing Degree Days: Because it is often inconvenient to obtain soil temperature data and often easier to track air temperature; consider using a growing degree day (GDD) model based upon air temperatures. Research suggests that 200 GDD need to accumulate with a base of 50 °F (http://www.gddtracker.net/?model=10&offset=0&zip=47905) before crabgrass germinates (source: Dr. Ron Calhoun). Currently (March 16, 2012), the models show that crabgrass still has not germinated in southern Indiana but that it is about to emerge. This still allows for the application of a preemergence herbicide if not yet treated.

Plant Phenological Indicators: The flowering of landscape plants can also be used as a good estimate of when crabgrass might be germinating. Many are aware that forsythia is traditionally considered a good plant to indicate that crabgrass will soon start germinating. Forsythia will be in full bloom prior to crabgrass germination and forsythia flowers will wither near crabgrass germination (Masin et al., 2005; Cardina et al., 2011). Most think that crabgrass germinates when forsythia blooms, but this is false. Instead, turf managers should use forsythia blooms as an encouragement to hurry up and get their preemergence application made before crabgrass begins to germinate. Other plants common in the landscape that bloom before crabgrass germinates include saucer and star magnolia and Bradford Callery pear (Cardina et al., 2011). The initiation of redbud blooms and sometimes crabapples are also a good indication of when crabgrass may germinate (Cardina et al., 2011). However, having said all this, researchers have also documented that ornamental plant flowering is not always a consistent predictor of crabgrass germination, especially with forsythia (Fry et al., 2001).

Sources

1. Cardina, J., C.P. Herms, and D.A. Herms. 2011. Phenological indicators for emergence of large and smooth crabgrass (Digitaria sanguinalis and D. ischaemum). Weed Technol. 25:141-150.
2. Fidanza, M.A., P.H. Dernoeden, and M. Zhang. 1996. Degree-days for predicting smooth crabgrass emergence in cool-season turfgrass. Crop Sci. 36:990-996.
3. Fry, J., S. Rodie, R. Gaussoin, S. Wiest, W. Upham, and A.Zuk. 2001. Using flowering ornamentals to guide application of preemergence herbicides in the Midwestern U.S. International Turfgrass Soc. Res. J. 9:1009-1012.
4. Masin, R., M.C. Zuin, and G. Zanin. 2005. Phenological observations on shrubs to predict weed emergence. Int. J. Biometeorl. 50:23-32.
5. Myers, M.W., W.S. Curran, M.J. VanGessel, D.D. Calvin, D.A. Mortensen, B.A. Majek, H.D. Karsten, and G.W. Roth. Predicting weed emergence for either annual species in the northeastern United States. Weed Sci. 52:913-919.

Snow mold damage - 2011

Melting snows revealed some significant snow mold damage. As you know there are two types of snow mold diseases, gray snow mold (aka Typhula blight) and pink snow mold (Microdochium patch). Although they create similar symptoms (circular patches of tan turf—sometimes with orange/brown margins, Fig. A, C, D) the pathogens are not closely related and they have different temperature requirements for infection. Infection by the gray snow mold pathogen occurs within a narrow range of cold temperatures (32 – 36 degrees Fahrenheit). The insulating effect of snow cover offers extended periods when such temperatures are maintained at the turf surface. Gray snow mold is not common in Indiana, but I have found plenty of it where snow piles have remained all winter. The gray snow mold pathogen produces survival structures called sclerotia (Fig. B) that are about the size of a period printed on this page.

Pink snow mold is much more common in the lower Midwest because infection occurs under a wide range of temperatures (32F – 50F). Symptoms that develop after snow melts, during cold wet weather in spring are attributed to the Microdochium patch phase of the disease. The pathogen produces spores (called conidia) at the edge of circular patches. The conidia may be washed down slope to create new infections, especially on putting greens. Juvenile (less than one year old) creeping bentgrass is unusually susceptible to snow mold damage.

At this time of year, controlling gray snow mold is all about hastening recovery of the patches. Because of the narrow range of temperatures required for infection, the disease will not spread any more this year. Disturbing (raking) the matted turf and perhaps a light application of N will accelerate turf growth as temperatures rise and mitigate the effects of the disease.

We treat pink snow mold differently because it remains a threat through April and May. I do not think fungicides are warranted for fairways, but I would consider an application on tees and putting greens if numerous patches developed over the winter. Turf within the patches are thinned by disease progress and therefore are vulnerable to colonization by Poa annua. It is likely that only a contact fungicide (chlorothalonil) will limit spread while turf remains dormant. Once turf is actively growing, a penetrant fungicide (such as a DMI) may provide more effective control.

For more details about snow mold diseases check out our Turfgrass Disease Profiles on the Turf Program Website--- www.agry.purdue.edu/turf/pubs/index.htm


Rick Latin, Turfgrass Pathologist
Aaron Patton, Turf Extension Specialist

Rejuvenating Turf in 2011: Part II

Part II: Preemergence and postemergence herbicides for crabgrass control in newly seeded areas
This turf tip is part of a three part series on spring seeding.

Early spring preemergence herbicides are often necessary in Indiana to prevent troublesome annual grassy weeds such as crabgrass and goosegrass. Additionally, these applications help to prevent the emergence of some broadleaf weeds. Most preemergence herbicides work to kill weeds by preventing cell division causing death to weed seedlings shortly after they germinate. All preemergence herbicides (except Tupersan) work to prevent the emergence of turfgrass seeds as well as weed seeds, so do not reseed areas treated with a preemergence herbicide this spring or do not apply a preemergence herbicide if you plan on seeding.

How to control crabgrass in lawns this spring

There are five potential options.

Control crabgrass as normal with a preemergence herbicide (dithiopyr, prodiamine, or pendimethalin) because the turf is not severely damaged and thin areas will fill-in from Kentucky bluegrass rhizomes. NOTE: If the lawn is tall fescue or perennial ryegrass it will not fill-in thin areas without additional seeding.

Tupersan (siduron) may be used for preemerg­ence control of annual grassy weeds in newly seeded cool-season turf and zoysia­grass. Check the label for rates and use directions. This herbicide is more expensive and short-lived, but it is the only safe preemergence herbicide to apply at the time of seeding.

Another strategy is to use a postemergence herbicide instead of a preemergence herbicide to control crabgrass in late May and June that is safe to use on seedling turf. Options include Drive (quinclorac), Tenacity (mesotrione), and SquareOne (quinclorac + carfentrazone). These products can be most safely used very soon after seeding to control crabgrass (see label for exact details on each turf species). If the seedlings are more mature (have been mown 2-3 times following their emergence) then other products such as Q4 Plus (quinclorac + sulfentrazone + 2,4-D + dicamba), Onetime (quinclorac + MCPP + dicamba), or Solitare (quinclorac + sulfentrazone) can also be used. For homeowners, there are now several products that contain quinclorac which can be used. Look for quinclorac in the list of ingredients on the label. NOTE: Tenacity (mesotrione) mentioned above can be used on all turf areas except residential home lawns at the time of this writing; however, a residential lawn label is anticipated for this product in the spring of 2011.

A fourth option is to use Dimension (dithiopyr) in May after a spring seeding to control newly germinated crabgrass that has emerged and is still at the 1-2 leaf stage or just started tillering. Dimension is the only preemergence herbicide which has good postemergence activity on newly germinated crabgrass. This application would also prevent future crabgrass germination through the rest of the summer in newly seeded areas. Another modification of this strategy would be to tank mix Barricade (Prodiamine) or Pendulum (Pendimethalin) with a post-emergence crabgrass product like Acclaim Extra (fenoxaprop), Drive (quinclorac), other quinclorac containing products, or Tenacity (mesotrione) in order to get both preemergence and postemergence control of crabgrass in a newly seeded area. The assumption with all of these herbicide options in this scenario is that the seedlings were planted in early spring and that they have developed enough of a root system to tolerate an application of a preemergence herbicide in May.

The last option is to go ahead and apply a preemergence herbicide to control crabgrass despite the fact that the lawn may be thin and in need of seeding. Since establishing turf in the spring is not as optimal as establishing turf in the late summer (mid-August to mid-September), you might likely have better long term results if you wait to seed in the fall as opposed to seeding this spring. This will only be an option for those patient enough to wait until they get their lawn back into shape.


Aaron Patton, Assistant Professor/Turfgrass Extension Specialist

Unwinter, Poa seedheads and Growing Degree Days, Oh MY!!!

As the “un-winter of 2015-2012” rapidly winds to a close golf course managers are already bringing their playing surfaces into peak form. For those managing putting surfaces containing annual bluegrass (Poa annua) this means addressing concerns that seedheads are affecting surface smoothness. With the lack of snow cover this past winter, the seedhead season is already off to a rapid start and seedheads in putting green turf are developing quickly! There are several cultural practices that can help minimize seedheads but treatment with a chemical plant growth regulator (PGR) provides the most consistent suppressive results.

Product choices: PGRs have been used for many years and currently there are not many new chemistries on the market. Historically, the most reliable choices have been; mefluidide (Embark or Embark T/O = less formulation) and ethephon (Proxy, several other brand names) or an ethephon + trinexapac-ethyl (TE:Primo Maxx, T-Nex and many other brand names) tank-mix. Mefluidide is normally a one time application thus, proper application timing is essential to success (unfortunately all plants do not produce seedheads at the same time/rate). Many consider it the “gold standard” for seedhead suppression. Any dissatisfaction with this product has been related to the missing the ideal application window and the risk for turf yellowing, particularly for Kentucky bluegrass surrounds. Many managers have moved away from using mefluidide on putting surfaces but it is still frequently used for higher cut fairway turf.

A popular alternative with very good suppressive properties is the ethephon + TE tank mix. The purported main advantage to the ethephon + TE combination is that the addition of TE with ethephon will minimize the yellowing (a “Granny Smith” apple green color) compared to ethephon applied alone. Additionally, the ethephon + TE combo is involves multiple applications (a second application should occur approximately 21 days following the first) which brackets seedhead development. Thus, many managers report more consistent seedhead suppression with this tank-mix compared to the single mefluidide application.

The use of other plant growth regulators like paclobutrazol, flurprimidol or TE alone, only slightly suppresses or delays seedhead emergence. These PGRs will not, however, minimize the seedheads to the extent of a mefluidide or ethephon + TE tank-mix. The addition of TE with ethephon also enhances turf color, however, research has shown where ethephon applied alone or tank-mixed with TE significant scalping (Dernoeden and Pigati, 2009) can occur when a TE program is not continued. Another consideration with any of the seedhead products would be the inclusion of a chelated iron source. This will further enhance green color and mask any potential PGR discoloration.


Timing: There are a number of managers who still use the “feel”, experience or local knowledge method to determine application timing. Another suggestion has been to initiate a seedhead program based after the second “true” mowing or when the turf is actively growing. While prior experience should still be a part of the decision to initiate, there are also more quantitative methods to help make this decision. Several models are available based on accumulating growing degree days (GDD) or heat units. The GDD models are based on the high and low air temperatures and utilize a “base” temperature. The most common method for calculating GDD is:

GDD = (max temp + min temp)/2 - “base temperature” (normally either 32 or 50 F)

Example: If we had a day with a maximum temperature of 76 and a minimum of 50 and used a base temperature of 50 the calculation would be: GDD = (76 + 50)/2 - 50 = 13, or for this single day 13 GDD. Remember there are no negative GDDs, a negative number is considered a zero and GDDs are summed across time (e.g. GDD day 1 = 3, day 2 = 4, day 3 = 15 would be 22 GDDs). You can do this on your own with a spreadsheet program and the weather data, but in our region (IN, IL, MI, OH) the growing degree day tracker located at www.gddtracker.net is an extremely useful tool that calculates for you.

Differences in base GDD temperatures? In prior years a base temperature of 50 was once used. Research conducted at Michigan State suggested that the GDD 50 base model often overestimated a few early warm days in the season and due to the higher base temperature and low number of GDD units required to reach the application threshold the model quickly passed the application target range. Thus, the GDD50 model is no longer used and a base temperature of 32 now used for the www.gddtracker.net model.

What to do? This spring (2012) GDDs have accumulated quite rapidly. The target for initiating an ethephon + TE program is normally between 200 and 250 GDDs, some suggest a specific number 220 and applications will be out of range at 500 GDD. In other words managers that start once 500 GDD accumulate should expect less than satisfactory results.

For many, in the region it is already time to apply the initial ethephon + TE tank-mix. For example, in Indianapolis this past Sunday (11 March) saw GDD exceed the initial threshold of 200 at 228 GDD and today (15 March) GDDs are predicted to be 320. In Lafayette, the initial threshold was met on Monday (3-12) at 236 GDD and today we will see 300 GDD. Way up north in Bristol the initial threshold will be met today at 212 GDD.

The take home point is that it is time to start treating for seedheads and as I talk to people in Indiana this initial application is about 11 to 14 days sooner than when they applied last year. The models are tools along with experience and as you gather “quantitative information” for your 2012 agronomic plans don’t forget to check out our tools on the Purdue Turfgrass Web-site www.agry.purdue.edu/turf as well as other online tools like Syngenta’s Pest Outlook Maps http://www.greencastonline.com/tools/PestOutlooks.aspx

Reference:
Dernoeden, P. H., and R. L. Pigati. 2009. Scalping and creeping bentgrass quality as influenced by ethephon and trinexapac-ethyl. [Online]Appl. Turfgrass Sci. p. 1-7.

Activity of Turfgrass Pathogens

A new posting has been added to Turfcast.

See Turfcast (http://btny.agriculture.purdue.edu/turfcast/) to read more about this post and for a daily summary of risk for several turfgrass diseases.

Rick Latin, Turfgrass Pathologist

Use Purdue Plant Doctor Apps for Android and iPhones to Fix Plant Problems

Correct diagnosis is the most important step you can take toward fixing plant problems. We took the best photos we had in our libraries and put them in our apps to help you become better plant managers. The Purdue Plant Doctor suite of smart phone apps will help you diagnose and find recommendations to manage the most common insect, disease and environmental problems on the most common trees and flowers in the landscape. Our apps are a pocket encyclopedia that uses over 2000 photos to identify and fix more than 200 problems on over 200 kinds of plants.

You can diagnose problems with our apps in three easy steps. First identify the kind of plant that has the problem. So, for example, if you are using the Purdue Tree Doctor, choose the kind of tree (eg. oak, maple, or pine) to narrow your search. Second, you choose the part of the plant that looks bad (leaves, flowers, branches, trunk or roots) to narrow your search even further. Third, you match the problem on the plant with our photos by swiping through our collection of high resolution photos. To save you time, the app arranges the photos for each of the plants so that the most common problems show up first! You can confirm your diagnosis by reading details linked to the photo.
If you already know the problem you have, just skip the diagnostic process and look it up from a list. Then you can get detailed information about the damage the problem can cause, its life cycle and how to control it with some combination of cultural practices and, if needed, a pesticide or fungicide.

All three apps, the Purdue Tree Doctor ($1.99), the Purdue Perennial Doctor ($0.99), and the Purdue Annual Doctor ($0.99) are available from the iTunes store. Although not yet optimized, it can be downloaded into your iTunes library and then loaded onto an iPad, where you can enjoy the larger pictures and format. 

The Purdue Tree Doctor is now available for Android in the Google Play Store for $1.99. This version will work on all Android devices including small and medium sized tablets.

Keep up on the latest versions and eventual release of Android versions of all three apps by checking the Purdue Plant Doctor website: https://purdueplantdoctor.com/

Cliff Sadof, Department of Entomology and Janna Beckerman, Department of Plant Pathology Purdue University

Warm-season Turf Winterkill 2014: What Can you Expect and NOW WHAT?

With colder than normal temperatures in Indiana this winter, we are anticipating some minor winter damage. To help prepare for this we are publishing a three part series on this topic to help turfgrass managers prepare for what may await them in the spring. Look forward to the following topics over the next week.

Part I: Warm-Season Turf Winterkill 2014: What Can you Expect and NOW WHAT?
Part II: Cool-Season Turf Winterkill: Potential Losses and a Pathway to Recovery
Part III: Snow Molds in the Winter of 2015-14

--
Warm-season Turf Winterkill 2014: What Can you Expect and NOW WHAT?
Predicting winterkill is a difficult task because turf can suffer low temperature injury in a variety of ways. The three most common ways that turfgrasses sustain low temperature injury are:

1. Sustained low temperatures
2. Low temperature spikes (freezing/thawing/freezing cycles?)
3. Unseasonably warm temperatures followed by freezing temperatures in late winter or early spring

Sustained low temperatures. Recently we fell in this category when unseasonably cold temperatures occurred. During this period, numerous nights less than 0 °F with average temperatures that were 10-20 °F below “normal”. Many locations have, however, had snow-cover which can insulate the turf and protect it during these very low temperatures.

Meyer zoysiagrass fairway in southern Indiana. Photo credit Andy Eble.

Low temperature spikes. In many cases turfgrasses can survive one or two nights of very cold temperatures because soil temperatures are more highly buffered than air temperatures and do not change as rapidly. Some turfgrass species such as zoysiagrass and bermudagrass have underground stems (rhizomes) which are insulated from the air temperatures and may allow them to withstand sudden drops in air temperatures. Snowfall helps to insulate soils and protect against these temperature spikes but southern Indiana lacked snow cover during our first set of cold spikes in early January and during our recent cold spikes.

Unseasonably warm temperatures followed by freezing temperatures. Warm-season grasses such as bermudagrass enter winter dormancy in late October and remain dormant until April/May. If their winter dormancy in interrupted by unseasonably warm temperatures in March/April which is then followed by freezing temperatures, winter injury can result. It is these conditions that still have the potential for more winterkill conditions in the upcoming late winter/early spring months in our region.
Plant cells are protected from freezing stress by many mechanisms, including the accumulation of certain proteins and enzymes as well as certain sugars and amino acids. When winter dormancy is interrupted by a period of unseasonably warm temperatures, the balance of these protectants in the plant cell changes and predisposes them to greater injury if freezing temperatures follow.

Which areas are more likely to suffer winterkill?

1. “In general” bermudagrass (particularly older cultivars) is more likely to winterkill than zoysiagrass
2. North facing slopes
3. Heavily shaded areas
4. Poorly drained areas
5. Heavily thatched turf
6. Areas planted with poorly adapted cultivars
7. Areas heavily trafficked during winter
8. Areas with deficient levels of soil potassium (K)
9. Areas lacking snow cover to insulate the soil

How can we estimate our losses? To help determine just how much winter injury you might have following these steps.

1. Collect samples using a cup cutter, shovel or trowel from areas that you feel may be damaged (low areas, shaded areas, uncovered areas) as well as from other areas not likely damaged (full sun, south facing slopes; areas planted with a cold tolerant cultivar/specie) or areas with a history of early spring green-up. Make sure that the sample you collect is at least 3 inches in diameter and is at least three inches deep.
2. Clearly label each sample denoting the date and location where it was collected.
3. Place the samples in a warm area (room temperature or above). Provide lighting and water the plugs when necessary.
4. Observe the plugs over the next two-three weeks. Alive plants should start to green-up (initiate new leaf growth) within 14 days. Differences in green-up between plugs collected from different areas should provide information on whether the plants survived the freezing temperatures. This will help as you begin to make decisions and plan for recovery.

Preparation and recovery: What should you do or not do this spring to help your turf?
Spring management practices including whether or not to apply spring preemergence herbicide applications should be based upon your winterkill likelihood estimates.

1. Damage not likely (minimal)
2. Moderate damage expected
3. Severe damage expected

Damage not likely. Some may have little fear of winterkill including those who have ‘Meyer’ zoysiagrass, a cold-hardy cultivar of bermudagrass (Riviera, Patriot, Northbridge, Latitude 36, Yukon, Quickstand), or those predominantly growing cool-season grasses such as turf-type tall fescue or Kentucky bluegrass. If you fall into this group consider yourself lucky. While we don’t have as much data on newer bermudagrass cultivars like Latitude 36 and Northbridge, we anticipate that they will have good survival. Particularly if not heavily trafficked late in the season. Those who have little fear of winterkill may go ahead as usual and make their scheduled preemergence herbicide applications this spring.

Moderate damage expected. Those who manage areas of bermudagrass that are partly shaded and common bermudagrass stands known to thin in prior difficult winters should expect some turf loss. It is too early to tell whether this damage will be minimal, moderate, or severe, but some level of winterkill should be expected. See below for preemergence herbicide strategy for these areas.

Severe damage expected. Common bermudagrass in southernmost Indiana like Evansville, Corydon, and New Albany that historically thins in winter or is slow to green-up. These areas did not have snow cover to insulate the soil and direct low temperatures injury may be expected.  See below for preemergence herbicide strategy for areas anticipating winterkill.

Preemergence herbicide strategy for areas anticipating winterkill. Early spring preemergence herbicides are often necessary in Indiana to prevent troublesome summer annual grassy weeds such as crabgrass and goosegrass. Most preemergence herbicides work to kill weeds by preventing cell division causing death to weed seedlings shortly after they germinate. These products can also affect the rooting of established turfgrasses, especially when new stolons begin to initiate roots. Ronstar (oxadiazon) is the only preemergence herbicide that will not affect the rooting of stolons that are trying to recover following winterkill.  Additionally, all preemergence herbicides work to prevent the emergence of turfgrass seeds as well as weed seeds, so do not reseed areas treated with a preemergence herbicide or do not apply a preemergence herbicide if you plan on seeding.
Therefore, if you expect some level of winterkill then it is advisable to skip or delay your preemergence herbicide application this spring. Focus on letting your turf to green-up this spring, and perhaps consider a post-emergent option.

If little winterkill is noticed, then you may go ahead and apply your preemergence herbicide application after green-up. You may consider tank-mixing a postemergence herbicide in the tank as well to control any emerged crabgrass or just using Dimension (dithiopyr) since it has both preemergence and postemergence activity.

If moderate winterkill is noticed after green-up then you will either need to regrow these areas either by 1) waiting for the existing turf to recover (aided by increased “light fertilization” :0.2-0.4 lb. of actual N/1000) or by 2) reestablish these areas from sod, sprigs, or seed depending on the species and cultivar present. If you choose to wait for the existing turf to recover then use postemergence herbicides to control existing weeds. If you need to replant from sod, sprigs, or plugs then you should control weeds  with a postemergence herbicide or use Ronstar as your preemergent source (always follow label directions). If you wish to seed bermudagrass to help recover areas, consider reading this linked publication from the University of Arkansas.

If severe winterkill is noticed after green-up then you will either need to reestablish these areas from sod, sprigs, or seed depending on the species and cultivar present. If you need to replant from sod, sprigs, or plugs then you should control weeds with postemergence herbicides. Newly planted turf is more susceptible to herbicide injury than established turf, so please consult herbicide labels to see when these products may be applied after planting. For instructions on seeding. See the above link.
Another strategy to speed bermudagrass spring recovery is to dormant seed bermudagrass into areas where damage is expected.  The basic approach is to scarify the areas with a verticutter or core-arefier and apply seed while temperatures are still cold (March and April). When soil temperatures warm in May, those seeds will germinate and hasten the establishment. If there is no rainfall be sure to supply irrigation and control weeds using a postemergence herbicide after bermudagrass seedlings have emerged. Instructions regarding dormant seeding of bermudagrass can be found in the above linked publication.

Planning and planting improved cultivars for a better future.
Southern Indiana lies in the transitional climatic zone. What this means is that summer in Indiana is too hot for cool-season grasses to perform well all year and winters are often cold enough to periodically injure warm-season grasses. Unfortu­nately, maintaining turf in the transition zone is more difficult than in many other parts of the United States.

The genetics of the plant is the most important factor that will decide whether or not a plant can survive winter. It is extremely important to choose and plant a cultivar with good winter hardiness when planting a grass at the northern fringe of its adaptation zone. Bermudagrass cultivars like Riviera, Patriot, Northbridge, Latitude 36, and Yukon are reliably cold-hardy in southern and central Indiana (we have tested as far north as West Lafayette). None of the hybrid bermudagrass cultivars and many of the common bermudagrasses are not well-adapted to Indiana.  After this winter, we will learn more about which cultivars are best adapted to our region.

The majority of zoysiagrass used in Indiana is Meyer (Z-52, Amazoy) or Zenith (seeded variety) and should survive this winter just fine based on our previous research.

 

Practices to enhance winter survival in subsequent years.

Choosing a cold-hardy cultivar and keeping it healthy is the best thing you could do to enhance the cold hardiness of the turf you maintain.  Although certain cultural practices may affect winter hardiness, they do not affect cold hardiness nearly as much as cultivar selection.
Below is a list of maintenance practices or maintenance issues and their effect on winter hardiness.

1. Nitrogen fertilization
2. Potassium fertilization
3. Plant growth regulators
4. Mowing height/frequency (traffic patterns/clean-up passes)
5. Soil drainage
6. Shade
7. Snow cover and blankets/covers
8. Sand topdressing
9. Traffic/soil compaction
10. Disease

Late-season Nitrogen:
Recent research on bermudagrass found that “reasonable” late-season N applications prior to frost promotes fall color retention and does not have a negative effect on bermudagrass winter hardiness. Late-season fertilization is highly recommended for athletic fields and some newly established turf. The only downside to this practice is that it may increase winter annual weed pressure and may predispose bermudagrass to more injury from diseases like spring dead spot or large patch disease.

Late-season Potassium (K):
Potassium is thought to also improve winter hardiness in some situations. As a result, it is commonly recommended that a “winterizer” fertilizer containing a higher ratio of K be applied in autumn prior to winter dormancy. However, research shows that additional autumn K fertilization will not reduce winter injury “if” a soil test indicates that your soil has optimum levels of K.

PGR’s:
Plant growth regulators applied prior to winter dormancy are thought to possibly increase winter hardiness. The theory is that if the plant is not using the energy for increased growth, energy is going into storage. Researchers have tried to document this effect, but no increase in cold hardiness has been documented from applications of PGRs like Primo (trinexapac-ethyl) prior to winter. In summary, PGRs are not going to hurt the plant, and not enough evidence exists to show they help.

Mowing:
It is thought (not scientifically proven) that increasing the mowing height at the end of the season slightly by 0.25-0.5 inches (or skipping the last couple of mowing) will help increase winter hardiness. This should in theory increase the leaf area available for photosynthesis, allowing for more energy production and more energy (carbohydrates, proteins, etc.) storage. Additionally, the extra leaf area will also serve to increase traffic tolerance by providing more cushion above the turfgrass crown and the soil.

Improve soil drainage:
Grasses grown in poorly drained areas, or chronically wet soils are more likely to winter kill. Ice accumulation in these areas during the winter can cause direct kill. Make sure to correct/improve surface and sub-surface drainage in low lying areas of golf course fairways and other turf areas to reduce the likelihood of winter kill.

Shade:
Shaded turf areas are less productive in producing and storing plant foods, they also stay cooler in the winter months. These cooler temperatures allow the soil to stay frozen longer, ice, snow and frost to remain on the surface longer. As a result, these areas can stay 5 degrees (F) or cooler during the winter and lead to increased winter injury. Bermudagrass turf in shaded areas is more prone to winterkill. To remedy this situation, decrease the amount of shade if possible, renovate with a more cold hardy cultivar or species (lihttps://www.blogger.com/blogger.g?blogID=446821120832903788#editor/target=post;postID=2841786949531260215;onPublishedMenu=posts;onClosedMenu=posts;postNum=21;src=postnameke zoysiagrass or other cool-season grasses).

Covers:
Blankets serve to reduce winter drying (desiccation) and to help retain heat. Blankets are used in southern states for hybrid-bermudagrass greens when night time temperatures are below 28 degrees (F) to help protect the soil from getting too cold and killing the bermudagrass. A good snowfall also acts as a nice cover. Where chronic winter injury is expected covers or blankets should be utilized to protect your investment.

Topdressing:
A less expensive alterative to covers that will help increase retain soil temperatures is to apply a moderately heavy application (1-4 cubic feet per 1000 ft2) of sand topdressing sand immediately prior to the onset of winter. This topdressing helps protect the crowns and reduces desiccation (drying). The dark-color topdressing also helps attract additional solar radiation and usually will results in a minor increase in soil temperatures which could also help to reduce winter injury. This technique might help reduce winterkill somewhat (theoretical) but the impact is likely small compared to covers.

Traffic:
Traffic is a stress and excess mechanical damage can predispose a plant to winterkill or accentuate winterkill. Avoid all additional stresses on turf prior to entering winter dormancy. Also, remove traffic from areas during winter, especially when temperatures are at, near, or below freezing. If traffic is necessary on athletic fields after warm-season grasses enter winter dormancy, rotate traffic to reduce the level of injury. Keep carts on paths on golf courses to reduce injury potential. Do not open areas to play when soil temperatures are near or below freezing.

Disease:
Spring dead spot (SDS) is generally considered to be the most significant disease of bermudagrass. This disease becomes evident at spring green-up but the pathogen actually infects and damages the bermudagrass in the fall. Fungicide control is difficult and inconsistent, but factors like nutritional status and thatch depth do play a role in the severity of the disease. Research is ongoing at Purdue University to help provide solutions for this turf disease.

Aaron Patton and Cale Bigelow, Purdue Turfgrass Program

Updated from previous postings at:
http://turf.uark.edu/turfhelp/archives/011810%20winter2010.html