April 19, 2005
To: Michigan Golf Courses
From: Michigan State University Turfgrass Faculty
Re: Winterkill damage on turfgrass
The past winter was no treat for turfgrass on golf courses in Michigan. Golf courses throughout the state have suffered from what is commonly referred to as winterkill. Winterkill is a general term that is used to define turf loss during the winter. The different types of winterkill include: crown hydration, desiccation, low temperature kill, ice sheets, and snow mold. Due to the unpredictability of environmental factors, and differences in other factors such as drainage, the occurrence of winterkill on golf courses is variable and can vary greatly between golf courses and even across the same golf course. The most common type of winterkill seen this year is from crown hydration injury, desiccation, and snow mold.
Crown Hydration Injury and Ice Sheets
Many annual bluegrass (Poa annua) greens and fairways suffered winterkill from crown hydration injury. The problem occurs in late winter, when day time temperatures became warm enough that the annual bluegrass plant begins to take up water (hydrate). It is possible that this occurred during the early March thaw from March 5-7 when, for example, temperatures in the Lansing area reached a high of 48° F and then as a cold front moved through dropped to a low of 13° F on March 8. During this period there was a significant melting of snow and then refreezing of the water that had yet to drain away. During these thaw/freeze events, ice crystal formation can occur in the crown of the plant. Ice crystal formation will rupture the plant cells and ultimately cause the plant to die.
Ice sheets are often blamed for killing turf when in fact it is crown hydration and subsequent refreezing that has resulted in the kill. The reason for the confusion is that as snow melts and refreezes, creating ice sheets, the ice sheets are often in poorly drained areas where due to the standing water crown hydration can occur. As the ice sheet melts away, the area damaged closely mirrors where the ice occurred and therefore the conclusion that ice sheets caused the kill. Basically this is an academic question at this point because no matter the cause, the turf has died.
Annual bluegrass is more susceptible to crown hydration injury because it emerges from dormancy and begins taking up water earlier than creeping bentgrass. Creeping bentgrass remains in the dormant state longer, and therefore doe not take up water and become susceptible to crown hydration injury during the late winter period. The damage from crown hydration injury is variable throughout the state with some areas devastated and others untouched.
Winter desiccation is the death of leaves or plants by drying during winter when the plant is either dormant or semi-dormant. Desiccation injury is usually greatest on exposed or elevated sites and areas where surface runoff is great,
Steps in Recovery
Reestablishing turfgrass in damaged areas can be very challenging in the spring due to cool, cloudy conditions that often persist. Depending on the extent of damage, either seeding or sodding can be used to facilitate recovery. In areas where the turf was killed in a manner that there are well-defined margins between dead and living turf, it may be feasible to strip dead turf and sod the area. In areas where the kill was more scattered it may be easier to seed the area. Seeding can be difficult, especially on damaged areas of greens. Inter-seeding creeping bentgrass into dead areas on the greens has given mixed results. The best results with inter-seeding have occurred when the low mow, high density type creeping bentgrasses, such as the A and G series bentgrasses, have been used. Tools like the job-saver aerator attachment, which produces numerous small, shallow depth holes, also increases the success of an inter-seeding program. The inter-seeding process should continue on a weekly basis until the damaged area has completely recovered. On greens that are predominantly annual bluegrass, often it is better to scratch the surface of the dead areas to allow the annual bluegrass to germinate and fill in the voids. Keys to success for renovating winterkilled areas are to divert traffic from newly seeded areas, apply light fertilizer applications to stimulate growth, and irrigate to ensure that the seedbed or sod is moist throughout the establishment period. Although it is unpopular with golfers, in some situations it may be necessary to close greens or divert traffic from damaged areas of greens to facilitate recovery.
Snow mold damage
With the extended periods of snow cover throughout many areas of Michigan this past winter there are many golf courses that have had higher than normal incidences of snow mold. The damage we are currently seeing is the result of both Microdochium patch (pink snow mold) and Typhula blight (gray snow mold). Okay, so if you have some snow mold damage what can be done now. First of all it’s important to stay on your preventative fungicide treatment schedule throughout the spring because if we have a wet cool spring as we often do, pink snow mold can remain active through the middle of June. From a management aspect, brushing the turf to stand it up and applying a light fertilizer application to stimulate growth and recovery will help the turf to recover from damage.
Predicting when total recovery from winterkill damage will occur is difficult, it will depend on the weather. Let’s hope we have a warm and sunny spring. For further information and pictures of winterkill throughout Michigan please see www.turf.msu.edu.
Dr. Kevin W. Frank and Dr. J. M. Vargas, Jr.