TURF TIPS Turfgrass Tips is a service of the Illinois Turfgrass Foundation and UIUC Turfgrass Group. October 2002, No. 5 WHAT HAPPENED TO AUTUMN? The below average temperatures this October have pressed schedules to complete annual fall turf maintenance. Cultivation is being wrapped up, fertilization has taken place and as soon as the leaves are addressed most turfed areas will be ready for the onset of winter. While most of us are happy to see this slow time roll around, there is still some action to take on your turf to help it survive the near future. TWO TURF WINTERKILL SCENARIOS Winterkill is a term used to describe any type of turf injury during the winter period. The term winterkill falls into the same descriptive category as "summer stress complex". In this part of the world, turf injury during the winter months can be attributed to different environmental causes namely, desiccation and crown hydration damage or freezing injury. DESICCATION Desiccation means to dry up. A turf can suffer from desiccation in the winter months and the results can be quite severe. It occurs when air temperatures are above the freezing point. Evapotranspiration is still occurring through the turfgrass plant during these periods and there is not enough available moisture for this process. Desiccation on a turf in winter may be caused by either soil or atmospheric drought. Desiccation resulting from lack of soil moisture most often occurs when inadequate levels of precipitation have occurred and the soil is dry. Sites that are elevated, exposed to prevailing winds, and have a high incidence of surface runoff usually are affected most by this condition. If the lack of natural precipitation continues this winter, winterkill caused by soil dryness may be a common occurrence throughout our region. Desiccation can also occur when the soil has adequate moisture. This occurs when the atmosphere (air) favors rapid evapotranspiration. Though the soil may hold adequate moisture it is not readily available to the plant for several reasons: the soil water is frozen and unavailable, root membranes are less permeable at lower temperatures and the viscosity of water is greater at lower temperatures. PREPARING TURF TO AVOID DESICCATION There are several steps that turf managers can take to prevent winter desiccation of turf from occurring. The straightforward method of prevention is to irrigate the turf prior to the onset of soil freezing or snow cover. If the soil is not near field capacity, a final irrigation cycle may be used to bring the soil to this level before the systems are shut down and winterized. Note, it is very important not to saturate the soil beyond field capacity to minimize hydration of the turfgrass crown tissue (See following section). The other methods to reduce winter desiccation involve controlling the evapotranspiration from turf. These things involve changing the microenvironment of the turf to protect it from water loss. The first method is to create windbreaks to protect the turf from the drying action of the prevailing winds. Installing snow fence has become a popular method to protect turf from excessive winds. One added benefit of the snow fence (in the rare occurrence of snow accumulation) is further protection of the turf by the snow itself as a cover. In areas where there is a history of desiccation turf managers have used mulches or topdressing to protect the turf from drying out. Many turf managers now utilize synthetic covers on their turf to protect it from winter desiccation. There are many advantages to using protective covers for intensely managed turf including: Prevent desiccation by trapping moisture Reduce extreme low temperature effects to turf and soil Reduce the loss of fall applied fungicides to the leaf and crown tissues Stimulate early green up in spring Moderate fall temperatures on newly planted sites and protect seedlings CROWN HYDRATION DAMAGE (FREEZING INJURY) Crown hydration damage (CHD) can be a very destructive form of winterkill of fine turfgrass in our area. Though not fully understood CHD seems to be more prevalent when certain conditions exist in the plant and in the plant environment. What is crown hydration damage? The process is complex, but it involves water freezing in open spaces around individual plant cells in the crown portion (growing point) of the plant. The ice crystals forming around the plant cell pull water out of the cell causing dehydration inside the cell. The process causes irreversible damage to cell membranes and death to the individual cells. A hardened plant can tolerate this condition, but once a plant loses hardiness (a natural occurrence in late winter) individual cells lose the ability to combat the dehydration process and severe injury can occur. The process is still not fully understood but damage seems to be worse when certain environmental conditions are met. How do turfgrass plants prepare for winter or harden? All plants develop a tolerance or hardiness to cold temperatures. That hardiness serves as a defense against freezing. Turf plants develop hardiness by storing carbohydrates in cells found in crown and root tissues. The higher concentrations of these materials act as antifreeze that prevents ice crystals from forming within the cells. Moisture content in the plant tissues also decreases during the hardening process, and cell walls and membranes undergo changes that improve their ability to tolerate ice crystals. The hardening process begins in late summer with the onset of cooler temperatures and shorter days and can continue through early winter. Maximum cold-temperature hardiness is obtained after the turf has been exposed to sub-freezing temperatures. CONDITIONS NEEDED FOR CROWN HYDRATION DAMAGE TO OCCUR Crown hydration damage usually occurs when warm temperatures are followed by quick drops in soil temperatures below 20°F. Hardiness of plants are generally reduced at this time when exposed to thawing. Free moisture (usually from melting snow or precipitation) around the crown of the plant freezes and draws water from the cell. This form of winterkill is more likely to occur in early spring once the snow begins to melt and there is excessive moisture present. Exacerbating this problem can be low-lying areas where water sits, poor drainage, and heavy soils. COMBAT CROWN HYDRATION The best way to prevent winterkill is to encourage the turf to harden off naturally. Steps that encourage the hardening process include: Providing adequate subsurface and surface drainage Do not encourage excessive top growth of turf by using excessive amounts of readily available nitrogen fertilizer late in the year Ensuring adequate levels of potassium through soil testing Do not over irrigate turfs late in the year beyond field capacity Control thatch through proper cultural practices Raise mowing heights before the temperatures drop Any cultural practice that encourages a healthy turf going into winter will aid survival for next spring.   Luke Cella, CGCS Editor Turfgrass Tips