Winter Kill

1. Winter Kill • Eliminating the myth of covering greens • All information gathered from the USGA, and the following Universities • Florida • Arizona • Clemson

2. Overview of Topics • Low temperature stress • Important temperatures • Turfgrass susceptibility to low temps • Cultural practices and their relationship with winter kill • Purpose of greens covers

3. Low Temperature Stress • Winter damage to bermudagrass is often referred to as “winter kill” • Winter kill is simply the loss of turfgrass during the winter or early spring

4. Types of Freezing Stress 1. Intracellular – Intracellular freezing causes ice formation inside cells, which occurs when cells are hydrated (not hardy), and a rapid drop in temps occurs. Most common in low, poorly drained areas, and is always fatal to the plant.

5. Types of Freezing Stress 2. Extracellular – Occurs when ice forms between cells. Routinely occurs in the temperate zone when temps drop below freezing. If temps stay cold for a long period of time, cells can become dehydrated to a point where injury or death results. Turf grown on sandy soils with low mowing heights is more susceptible.

6. Important Temperatures • < 60 F – growth slows significantly when the average daytime temperature drops below 60 • <50 F – grass begins to enter dormancy when average temperature drops below 50 • 34 F – 70 F – grass can continue to grow slowly when temperatures get as low as 34 as long as daytime temps are near 70

7. Important Temperatures • Permanent turfgrass injury to warm-season turf often occurs if ambient temperatures drop rapidly to below 23 F • Or drop gradually to below 10 F

8. Endangered Turf • One of the most dangerous events are extreme cold events following warm, dry temperatures that stimulate new growth • Especially dangerous in late winter, early spring

9. Uncontrollable Temperature Freeze and thaw frequency Freeze and thaw rate Freeze Duration Cultural Practices Drainage Fertility Irrigation Mowing Pest Control Soil Cultivation Thatch Level Traffic Turfgrass Susceptibility to Low Temperature Injury

10. Cultural Practices Effect on Winter Kill • Traffic – can crush frozen crowns, killing the plant. (dormant or not) • Drainage – poor drainage results in direct temperature damage to crowns

11. Cultural Practices Effect on Winter Kill • Moisture Deficiency – Desiccation is the leading cause of winter kill • Thatch – Excessive thatch elevates crowns and lateral stems above the soil

12. Cultural Practices Effect on Winter Kill • Excessive Desiccation – High winds, especially during periods of low humidity, often cause massive areas of winter damage, cold fronts that follow warm, windy weather often pose the most most severe threat

13. Cultural Practices Effect on Winter Kill • Close Mowing – Close mowing in late summer discourages deeper rooting and carbohydrate reserve accumulation which can contribute to winter kill • Verticutting – Late summer and fall verticutting deplete the plants carbohydrate reserve and make the plant more susceptible to winter kill

14. Purpose of Turf Covers • Turf covers may help protect the crowns from direct low temperatures and desiccation • Covers are not used to protect winter overseeded varieties, but rather to prevent a sudden temperature drop that could adversely effect the bermudagrass

15. Summary • Many people are under the impression that covers are used to protect overseed, but I hope that this information will aid with the understanding that turf covers are used to protect warm season turf from severe low temperature injury.

16. Summary • Death of leaf tissue during freezing is a common occurrence. However, if the crown suffers freezing injury, the plant will die.

17. Summary • When we use the turf covers we are trying to slow down a sudden temperature drop and hoping to minimize the extreme temperature damage to the crown of the plant. If the cold weather has a long duration covers won’t prevent winter kill.