Turfgrass and Site Specific Management High Temperature Stress in Cool-Season Grasses By: Kirk Castner

High Temperature Stress in Cool Season Grasses Natural cooling processes of turfgrass Supplemental irrigation and syringing techniques Addition of turf fans to increase air flow

Chemical Reactions & Temperature Temperature affects all chemical reactions Since metabolic pathways are fueled by chemical reactions, plant metabolism is directly affected by temperature When temperature increases, the rate of plant metabolism increases

Cool-Season Grasses & Heat Cool-season grasses perform best during temperatures between 60F and 75F The heat contained in a leaf is a result of solar radiation, metabolism, and heat reflected by surrounding vegetation or structures It is imperative that the leaf dissipate this excess energy or the plant will cease to function Heat may be dissipated through transpiration or conduction and convection

Conduction & Convection Conduction is the transfer of heat from a warm leaf to cooler air The upward movement of this warmed air and its replacement by cooler air is called convection

Convection & Transpiration As the leaf passes heat to surrounding air, this warm air rises away from the canopy and is replaced by cooler air Air movement around the leaf speeds the convection process and aids in transpiration

Plant Transpiration Plant transpiration is a cooling process starting with root absorption and ending with leaf evaporation Under normal circumstances, the relative humidity inside a leaf stomate is near 100% When the relative humidity of the air is low, transpiration occurs rapidly When the relative humidity of the air is high, little transpiration occurs Extremely high or extremely low relative air humidity are both detrimental to plant metabolism

Transpiration When sufficient water is available, most of the water absorbed by a plant, is transpired When water is limited, the plant's first line of defense is to limit transpiration by closing stomata Closing stomata avoids water loss but limits nutrient uptake and effects photosynthesis and other plant processes

Syringing Application of water to the leaf surface to cool the canopy. Checking greens – color and wilt. Localized dry spots Too much water can be just a detrimental as drought stress. A plant suffering from heat stress often will close its stomata even when adequate soil moisture is available. When this happens, it is unable to cool itself. A light application of water to the leaf surface-syringing-will provide evaporative cooling if the atmospheric relative humidity is low enough to for significant evaporation to occur. You should recognize the difference between syringing and irrigation, however. Syringing refers to wetting the leaf surface only. Bentgrass with a shallow root system could require midday watering to nurse it through the heat of the day.

Irrigation vs. Syringing Irrigation is used to water deeply and incorporate water into the soil profile for plant uptake. Syringing applies water to the canopy, but is not intended to restore soil moisture, as is a typical irrigation. Typically, superintendents syringe in the early morning to remove dew or at midday to moderate temperatures. Used to cool canopy as opposed to incorporate moisture into soil.

Root Mass During summer when solar radiation is high and the air is warm, cool-season grasses begin to lose root mass Most of the remaining roots are near the surface where the soil dries out quickly Short cut turf, with a shallow root system requires syringing when conditions are hot and dry Syringing has little effect when relative humidity is high and air movement is low because transpiration is not affected

Drought Stress  Heat Stress High air temperature and/or little air movement restrict conduction, convection, and transpiration If the turf is water stressed and stomata are closed, conduction and convection are the only means for the plant to dissipate heat Cool-season plants that are drought stressed become heat-stressed at lower temperatures than plants with adequate water

Turf Fans Alleviate stagnant air and excess moisture on surface. Better air circulation promotes overall healthier turf. Lower surface temperatures on greens up to 10 F 30, 36, and 50 inches Used on greens surrounded by trees or situated in low areas enclosed by berms that restrict airflow. Increase air movement. Wind helps increase the humidity gradient between the leaf and atmosphere so that water more readily transpires through stomata and cools the plant. Therefore, a bentgrass green surrounded by trees or situated in a low area enclosed by berms is prone to heat stress due to a lack of air movement. You can enhance air movement by removing vegetation and additions of fans.

Additional Stress Additional stress should be avoided during the warm summer months on cool-season grasses Topdressing and dragging Chemical applications Traffic

Covering & Topdressing Sport field managers should resist covering turfgrass when temperatures are high and covers should be removed immediately if the weather becomes sunny Turf managers should resist topdressing when temperatures become high because sand and soil particles absorb and reflect heat Heavy topdressing should only be done during cool weather

Topdressing & Dragging Topdressing and dragging is not recommended during the heat of the summer These processes cause damage that takes a considerable time to heal when plants are under summer stress Layers of sand can become extremely hot on sunny days and add to heat stress

Chemical Applications Chemical applications should be avoided if at all possible Formulations that are not toxic in the spring may be toxic in the summer due to the weakened state of the turf Herbicides are especially dangerous to turf in the summer

Traffic Traffic should be kept to a minimum and channeled into unused areas whenever possible. Turf should be monitored daily for signs of wilt or other stresses. Changing cup locations daily and monitoring stress throughout the day.

Questions?? Questions??