Winterkill

In this module, we will explore the phenomenon of winterkill, a significant challenge faced by turfgrass managers in regions with cold winters. Winterkill refers to the damage and death of turfgrass caused by various factors during the winter and early spring months. It can result in unsightly and unhealthy turf areas, leading to the need for renovation and recovery efforts. Understanding the causes and management strategies for winterkill is essential for maintaining healthy and vibrant turfgrass.

 

Check for Winterkill Damage

 

Credit: USDA

 

Causes of Winterkill

We will delve into the different causes of winterkill, including desiccation, anoxia, direct low temperature kill, and crown hydration. We will also discuss cultural and management practices to prevent winterkill and promote turfgrass resilience. It should be noted that preventing winterkill is not always achievable. All turfgrass species exposed to cold temperatures below their respective tolerance are susceptible to winterkill.

 

Direct Low Temperature Kill

Direct low temperature kill refers to the damage and death of turfgrass caused by extreme cold temperatures during the winter. When turfgrass is exposed to temperatures below its cold hardiness threshold, cellular damage occurs, leading to tissue death. This type of winterkill is more prevalent in regions with severe winter climates and extended periods of freezing temperatures. Several factors contribute to direct low temperature kill, including the inability of turfgrass to withstand prolonged cold exposure, ice formation within plant tissues, and freeze-thaw cycles that further exacerbate damage.

 

Symptoms

The symptoms of direct low temperature kill vary depending on the severity and duration of cold exposure. Initially, affected turfgrass may exhibit discoloration, ranging from yellowing to brown or black discoloration. As the damage progresses, the affected areas may become necrotic, appearing as dead patches or thinning turf. In severe cases, complete turf loss can occur, leaving bare soil exposed.

 

Causes

Direct low temperature kill is primarily caused by prolonged exposure to extremely low temperatures. Turfgrass species differ in their cold hardiness, with some being more tolerant to freezing conditions than others. Factors such as inadequate snow cover, sudden temperature drops, and temperature fluctuations during winter can increase the risk of direct low temperature kill. Additionally, poorly drained soils that retain excessive moisture can enhance the susceptibility of turfgrass to cold injury.

 

Management and Prevention

Proper cultural practices and management strategies can help mitigate the risk of direct low temperature kill in turfgrass. Here are some key measures to consider:

 

  • Species selection: Choose turfgrass species and cultivars that are well-adapted to the local climate and exhibit good cold tolerance.
  • Fertility management: Avoid excessive nitrogen applications in late fall, as they can promote lush growth and delay hardening-off, increasing vulnerability to cold damage.
  • Adequate drainage: Improve soil drainage in areas prone to excessive moisture accumulation, as saturated soils can enhance cold injury.
  • Snow cover: Encourage the formation of an insulating snow cover.

 

While it is challenging to prevent direct low temperature kill entirely, implementing these cultural practices can help enhance turfgrass resilience and minimize the extent of damage caused by extreme cold temperatures. Regular monitoring and prompt action in early spring to facilitate turf recovery will also contribute to successful winterkill management.

 

Desiccation

Desiccation is a form of winterkill in turfgrass that occurs as a result of excessive water loss and dehydration during winter months. It commonly affects turfgrass in regions with cold, dry winters or areas exposed to harsh winds. Desiccation is more likely to occur when the turfgrass is unable to replenish water lost through transpiration due to frozen or inaccessible water sources, frozen soil, or a lack of precipitation. The combination of low temperatures, dry air, and limited water availability places stress on the turfgrass, leading to cell desiccation and subsequent tissue damage.

 

Symptoms

The symptoms of desiccation are typically observed as browning or discoloration of the turfgrass. The affected areas may appear dried out, with the grass blades becoming brittle and prone to breakage. In severe cases, complete turf loss can occur, resulting in bare patches or thinning turf areas.

 

Credit: John Kaminski/Penn State University

 

Figure 9.6.1: Desiccation can occur where open putting green surface are exposed to high winds. Ensuring (a) adequate moisture or (b) covering greens with permeable or impermeable covers can help to reduce turf loss.
 
 

Causes

  • Dry winter conditions: Regions with low winter precipitation or periods of extended drought are more susceptible to desiccation.
  • Cold winds: Strong, cold winds increase the rate of water loss through evaporation and can rapidly dehydrate the turfgrass.
  • Frozen water sources: Frozen or inaccessible water sources prevent the turfgrass from replenishing moisture, leading to dehydration.
  • Frozen soil: Frozen soil restricts root access to water, reducing the ability of the turfgrass to take up moisture.

 

Management and Prevention

  • Adequate watering: Prioritize proper irrigation before winter to ensure the turfgrass enters the dormant season well-hydrated. This helps to increase water reserves in the plant and mitigate the risk of desiccation.
  • Hydration during dry periods: If dry periods occur during winter, consider supplemental watering when weather conditions allow, particularly during warm spells or thawed periods. This can help replenish moisture and reduce the risk of desiccation.
  • Windbreaks and barriers: Install windbreaks or barriers, such as snow fences or windbreak plantings, to minimize the impact of cold, drying winds on the turfgrass.
  • Improve soil moisture retention: Enhance soil moisture retention by improving soil structure and organic matter content. This helps the soil hold moisture for a longer duration, reducing the risk of desiccation.
  • Select drought-tolerant species and cultivars: Choose turfgrass species and cultivars that have demonstrated tolerance to drought and desiccation conditions prevalent in the region.

 

By implementing these management practices, turfgrass managers can minimize the risk of desiccation and promote healthier, more resilient turf during winter months. Regular monitoring of moisture levels and taking appropriate action to address water stress can help mitigate the impact of desiccation and support turfgrass recovery in spring.

 

Anoxia

Anoxia is one of the most problematic issues contributing to winterkill. Anoxia occurs when turfgrass is subjected to prolonged ice cover, leading to a lack of oxygen diffusion and subsequent damage to the plants. It primarily affects species like annual bluegrass and creeping bentgrass, which are more susceptible to anoxia when ice cover persists for an extended period. In this section, we will explore the definition, significance, symptoms, causes, and management strategies for anoxia in turfgrass. Understanding these aspects will help you mitigate the risks and promote healthier turfgrass during the winter months.

 

Symptoms

Anoxia in turfgrass can manifest with various symptoms that indicate the stress and damage caused by the lack of oxygen. These symptoms may differ depending on the turfgrass species and the severity of the anoxia. 

 

In some cases, the turfgrass on putting greens may initially appear normal after the ice melts, giving a false sense of recovery. However, despite the seemingly normal appearance, the turfgrass can gradually decline due to the underlying effects of anoxia. This delayed response is a significant characteristic of anoxia-related winterkill.

 

One distinct indication of anoxia is the presence of a rotten egg sulfur smell. This odor is a result of the buildup of anaerobic bacteria that thrive in environments devoid of oxygen. The accumulation of these bacteria produces hydrogen sulfide gas, which has a distinctive foul smell resembling rotten eggs. Detecting this odor can help identify the presence of anoxia in turfgrass areas.

 

Credit: John Kaminski/Penn State University

 

Figure 9.6.2: Anoxia occurs where prolonged periods of (a) ice cover occurs. Deeper (b) sheets of ice can often remain present for longer periods of time and therefore may lead to more severe damage. When snow on putting greens melts, it can move to (c) low lying areas and freeze resulting in severe damage. Ice that is (d) fractured can result in improved oxygen exchange resulting in lines of healthy turf which can be a diagnostic characteristic of turfgrass that has died from anoxia.
 

Causes

One of the primary factors is the duration of ice cover. Anoxia occurs when turfgrass remains under ice cover for an extended period. The duration of ice cover is a critical determinant in the development of anoxia. Turfgrass species vary in their susceptibility, with annual bluegrass typically requiring 45-60 days of ice cover, while creeping bentgrass can withstand ice cover for 75-90 days before anoxia occurs. Monitoring the duration of ice cover is essential to assess the potential risk of anoxia in turfgrass.

 

The amount of snow accumulation also plays a role in anoxia development. Snow acts as an insulating layer, protecting turfgrass from extreme cold temperatures. However, excessive snow accumulation can lead to prolonged ice cover, restricting the exchange of gases between the turf and the atmosphere. This lack of gas exchange creates anaerobic conditions, contributing to anoxia development. Managing snow accumulation and ensuring proper snow removal practices can help mitigate the risk.

 

Management and Prevention

In situations where anoxia is suspected, turf managers often resort to drilling through or breaking up a section of the ice to assess the condition of the underlying soil. By doing so, they can get a closer look at the soil and evaluate the presence of any foul odor associated with anaerobic conditions. The distinct rotten egg sulfur smell emanating from the soil can serve as a crucial indicator to determine whether the ice should be removed or if additional measures need to be taken to alleviate the anoxic conditions. This olfactory assessment method is a practical tool that turf managers use to make informed decisions about the management of anoxia-affected areas and prevent further damage to the turfgrass.

 

Management of anoxia in turfgrass requires various strategies depending on the grass species and specific conditions. Here are some key management practices for addressing anoxia in different scenarios:

 

  • Resodding: In severe cases where the turfgrass has been extensively damaged, resodding may be necessary. This involves removing the existing damaged turf and replacing it with healthy sod. Resodding provides an immediate recovery solution, especially in areas where the turf cannot naturally recover on its own.
  • Reseeding with annual bluegrass: If the affected turfgrass is primarily composed of annual bluegrass, reseeding with annual bluegrass seed can be an effective approach. Anoxia creates favorable conditions for the germination of annual bluegrass seed in the soil. Aerification or verticutting can help to bring up existing seed populations and create seed-to-soil contact and promote the germination and establishment of annual bluegrass.
  • Reseeding with creeping bentgrass: For turfgrass composed of creeping bentgrass, the optimal time for seeding is different. Bentgrass seed requires soil temperatures above 10oC (50°F) for successful germination. Therefore, early seeding attempts in colder conditions may not yield desired results. It is important to wait until soil temperatures are suitable before reseeding with creeping bentgrass. It is also important to note that some bentgrasses germinated better than others at lower temperatures.
  • Drainage improvements: Improving soil drainage is crucial in preventing and managing anoxia. Addressing any underlying drainage issues, such as correcting surface grading, installing drainage systems, or improving soil porosity, can help reduce the likelihood of prolonged water saturation and anoxia occurrence.
  • Utilize protective covers: The use of impermeable covers, such as geotextile or impermeable tarps, can help prevent the accumulation of ice and create a barrier between the turfgrass and the ice layer. Covers can be applied before the onset of prolonged ice cover to minimize anoxia risk and protect the turfgrass from the detrimental effects of oxygen deprivation.
  • Apply potassium fertilizer in the fall: Adequate potassium levels in turfgrass can help enhance its winter hardiness and resistance to various abiotic stresses, including crown hydration. Applying potassium fertilizer in the fall, according to recommended rates and timing, can promote the accumulation of potassium reserves in the turfgrass, improving its ability to withstand winter conditions and reducing the risk of winterkill. 

 

Crown Hydration

Crown hydration is a phenomenon that occurs in annual bluegrass, and to a lesser extent creeping bentgrass, during the spring when the plant undergoes deacclimation of its cold tolerance. It occurs when late winter or early spring freezes are followed by ice accumulation in the plant cells, leading to the puncturing and subsequent leakage of cell contents. This abiotic disorder can result in significant damage to turfgrass and is an important consideration for turfgrass managers.

 

Symptoms

One of the primary symptoms of crown hydration is the discoloration and wilting of turfgrass. Affected areas may exhibit a yellow or brown coloration, indicating the loss of vitality in the grass. The turfgrass may appear weak and thin, and its growth may be stunted or completely halted. In severe cases, complete or partial loss of the turfgrass stand may occur. Symptoms may not become apparent immediately but typically manifest as the weather warms up.

 

Credit: John Kaminski/Penn State University

 

Figure 9.6.3: Crown hydration occurs in the spring when (a) standing water freezes resulting in intercellular ice formation which can cause dehydration of the cytoplasm resulting in a (b) water-soaked appearance (c) ultimate death. In areas where snow melts during the day and then quickly refreezes over (d) drain lines, the resulting death is localized.
 
 

Management and Prevention

  • Improve drainage: Enhancing drainage in the turfgrass area is crucial to prevent water accumulation and reduce the risk of crown hydration. This can be achieved by implementing proper surface grading, installing drainage systems, or incorporating sand-based root zones that promote water movement and prevent waterlogging.
  • Create channels for water movement: Cutting out small channels or trenches in areas prone to water accumulation can help facilitate the movement of excess water away from the turfgrass. This can be done using specialized tools or equipment to create paths for water to drain, preventing it from damming up and causing crown hydration.
  • Reseed or resod damaged areas: If crown hydration has resulted in significant damage to the turfgrass, reseeding or resodding may be necessary to restore the affected areas. Reseeding with appropriate turfgrass species or installing new sod can help establish healthy vegetation and promote recovery.
  • Potassium: Similar to winterkill caused by anoxia, fall applications of potassium-based fertilizers can improve the turf’s tolerance to winterkill.

Credit: Golfdom Magazine