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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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.

10. 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.

11. 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

12. 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

13. 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.

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

15. 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

16. 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

17. 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

18. 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.

19. Questions?? Questions??