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 60F and 75F • 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.
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.
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.