Wet wilt and heat-related injury produce turf loss on putting greens in PA

July 26, 2010 in Extension

The unusually hot, dry weather occurring over an extended period in June and July have led to severe turf losses on putting greens in numerous locations around the state. Much of the damage can be traced to a phenomenon known as wet wilt. Wet wilt occurs when very high (>90oF) soil temperatures and low oxygen levels (due to wet soils) cause impairment of root function. The consequence of this is that roots cannot take up water fast enough to meet the transpiration cooling demands of Poa annua turf. Thus, on hot days with low humidity and wind, the turf begins to overheat, wilt, and eventually die, despite the fact that there is an adequate supply of water in the soil. Although overheating (sometimes called scald or supraoptimal heating) of turf is considered a separate cause of injury, wet wilt and overheating often occur together, making a bad situation worse.

The practice of syringing is the most common means of cooling the turf and reducing the chance of wet wilt and heat-related injury. Syringing involves applying a light spray of cool water over the turf surface to reduce plant temperatures. The key to successful syringing is to cool the plants without adding more water to the soil.

Wet wilt is more severe on Poa annua ‘push-up greens’ with drainage issues, and when root systems are shallow and near the soil surface (where they are exposed to high soil surface temperatures). Suggested preventative measures to reduce the occurrence of wet wilt episodes include improving drainage on the most wilt-prone greens, and promoting better root development. Although adequate drainage is always a challenge on push-up greens, the best method of achieving this is through a series of slit trenches that are back-filled with sand. This will allow surface water to flow through channels and move off the surface of the greens. Companies that are proficient in installing these systems are XGD Systems and Golf Preservations, Inc. It is important to realize that these systems will not prevent all drainage-related problems in the future. Soil-based push-up greens with low areas will still remain wet following heavy rains.

One means of improving root development in greens is through a regular program of core aeration (fall and spring), and perhaps deep-tine aeration. Holes that are produced by coring and backfilled with sand will allow roots to penetrate deeper into the soil and create more branching and increased surface area. Coring will also remove some thatch and mat (which may impede drainage and hold excess moisture). Although core aeration disrupts the putting surface, it’s a required maintenance practice that yields dividends down the road. Deep-tine aeration also will help create deep channels and fractures that encourage internal drainage and root development.

Applications of fungicides for control of Pythium, summer patch, anthracnose, and other summer diseases may help the turf survive during periods of high heat and humidity. A regular program of spiking and/or needle tine aeration will help toxic gases escape from soil and allow oxygen to diffuse into the root zone.