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 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.



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


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.

rate lbs/1,000 ft2
Days to
Kentucky bluegrass
1.0 to 2.0
Kentucky bluegrass (80-90%) + perennial ryegrass (10-20%)
3.0 to 6.0
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 (, 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:
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. (gray snow mold) (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.



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



  • 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.
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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
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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:

Cliff Sadof, Department of Entomology and Janna Beckerman, Department of Plant Pathology Purdue University
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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 2013-14

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.

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.

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.

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 (li;postID=2841786949531260215;onPublishedMenu=posts;onClosedMenu=posts;postNum=21;src=postnameke zoysiagrass or other cool-season grasses).

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.

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 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.

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:
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Snow Molds in the Winter of 2013-14

From a turf disease perspective, evidence of the severity of this winter is apparent in the extent of snow mold development.  Symptoms of Typhula snow molds (gray snow mold and speckled snow mold), and/or pink snow mold are obvious throughout Indiana and the Midwest.

Typhula snow mold pathogens are adapted to grow and infect at low temperature (32°F to 36°F), and infection occurs only under extended periods (45 days or more) of snow cover.  Snow molds are primarily leaf blighting diseases.  Crowns and roots are not affected, and symptoms usually fade in spring with turf recovery in spring.  Recovery may be delayed after severe outbreaks, sometimes allowing damaged areas to be colonized by annual bluegrass. 

On turf maintained at heights of 3/4 inch or less, Typhula snow mold infections result in nearly circular patches that are typically 6 to 12 inches in diameter (Figure 1). On taller mown turf, patches may be larger, but they may not be as well defined.  Snow mold patches enlarge by radial expansion of mycelium under the snow. The mycelium may be evident in the days during and after snowmelts. Small survival structures called sclerotia often are found embedded in dead leaf tissue within circular patches.  Gray snow mold fungi produce reddish brown sclerotia—speckled snow mold fungi produce dark brown or black sclerotia (Figure 2).  For the purpose of this article, it is not important to distinguish between the two.

Figure 1.  Well-defined circular patches characteristic of Typhula snow molds.

Figure 2.  Sclerotia are produced within infected leaf tissues.

Since outbreaks occur only under snow cover, fungicides applied to Typhula snow mold patches after snow melts will not lessen disease severity or hasten turf recovery.  At this time best results will be achieved by raking the damaged and matted areas to hasten turf recovery.  

Pink snow mold and Microdochium patch (formerly Fusarium patch) are two phases of a disease caused by a single fungal pathogen, Microdochium nivale. The phase that occurs under snow cover is referred to as pink snow mold.  When outbreaks occur in cold wet weather in the absence of snow it is referred to as “Microdochium patch.”  For both phases, infection and colonization result in a general leaf blight—crowns and roots reportedly are not affected.  All cool-season turf species are affected, but outbreaks tend to be most severe on creeping bentgrass and annual bluegrass on golf courses.  Moreover, juvenile creeping bentgrass (less than 1 year after seeding) is most susceptible to the disease and likely to suffer the most lasting effects.  Patches thinned by disease are more vulnerable to colonization by annual bluegrass. On mature golf greens, annual bluegrass appears to suffer greater damage.

On short-mown golf turf, pink snow mold symptoms include well-defined, circular patch clusters (Figure 3). On creeping bentgrass and annual bluegrass putting greens, streaks of off-colored turf that follow the green’s surface drainage patterns may appear during the spring. During cool, wet conditions, white-pink mycelium may be observed on infected leaf blades. Patches of dead, matted leaf blades also occur on taller mown turf, but often lack a clearly circular pattern.

Figure 3.  Pink snow mold infection results in 6”-12” circular patches.

The pink snow mold pathogen is active over a broad temperature range (30°F to 60°F), so infection may continue throughout the spring. Unlike Typhula diseases, snow cover is NOT necessary for extensive pink snow mold infection. However, the insulating effect of snow cover extends the duration of temperature favorable for disease development. The pink snow mold pathogen survives with infested leaf residue in the thatch and decaying turf debris—it produces NO sclerotia.

Spring maintenance also is important to hasten the recovery of turf damaged during the winter. Any practice such as raking and/or mowing that disturbs and aerates affected turf will limit further disease development in the spring and allow the turf to recover as temperature increases during spring.  Fungicides can be effective in preventing Microdochium patch increase on putting greens where infection may continue during periods of cold wet weather.

More detailed information about snow mold diseases is presented at the following links. (gray snow mold) (pink snow mold)

Rick Latin, Professor of Plant Pathology
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