Winter Diseases: There are two winter disease caused by fungal organisms that effect all cool season turf grasses. The first being Pink Snow Mold which is caused by Microdochium nivale, this can occur with or without snow, and is favored by cold wet conditions. The other disease is Gray Snow Mold caused by two Typhula species: Typhula incarnata and Typhula ishikariensis, this disease occurs under snow cover. Both of these diseases are typically not a concern with properly timed fungicide applications.
Direct Low Temperature Kill: This occurs when temperatures drop below the maximum level of freezing tolerances of the grass species. Once this happens ice crystals form within the plants puncturing cells. Snow cover provides insulation and usually prevents this from happening. Creeping bentgrass can tolerate temperatures as low as -30 degrees and annual bluegrass, often referred to by it's scientific name of Poa annua can tolerate temperatures of -5 degrees. There are even certain bio types of annual bluegrass that can tolerate temperatures up to -15 degrees. Perennial Rye grass is tolerant to about 5 degrees. This problem can become more troublesome during freeze/thaw cycles because the plants cold tolerance can be affected. For example a plant that was tolerant to -15 may only be tolerant to -5 after a cycle. The more cycles you have the less cold tolerant the turf becomes.
Desiccation: This usually occurs in the absence of snow with frozen ground. Plants that get damaged or killed from desiccation are usually exposed to cold winter winds. Transpiring plants will lose water from their leaves, and then are unable to replace that water loss. This is not very common because of snow cover. Higher areas are more prone to desiccation like bunker faces, peaks of hills or slopes.
Crown Hydration: This is a problem with annual bluegrass. Annual bluegrass can come out of dormancy with a couple of warmer days. These plants will begin to take in water, and the problem occurs once temperatures freeze again causing ice crystals to form inside the plant puncturing cells in the crown leading to severe injury or plant death. This is usually a problem during freeze/thaw cycles that you would have towards late winter, early spring. Can become very concerning on greens that have a lot of annual bluegrass.
Ice Damage: There are typically two types of ice that can form over the winter. One type is porous, like you would find in snow cones. This type of ice doesn't usually cause any issues because of pore space, which allows for oxygen and gas exchange. The more threatening ice is the type that is thick, dense and lacks pores, like you will find with ice cubes. This ice causes an impermeable layer at the surface of the turf which can restrict air exchange causing anoxia (suffocation). Creeping bentgrasses can tolerate ice cover for 90 to 120 days. Annual bluegrass can tolerate ice between 45 and 90 days. Most research indicates 60 days. However, research in Michigan is very difficult because winters are so inconsistent.
All of the above problems can occur almost anywhere on the golf course due to Mother Nature, but the greens are obviously the most critical and require the closest monitoring.
