Mid-to-late June normally is when the first sustained, hot and sultry days move into the mid-Atlantic. Sometimes, this weather is accompanied by heavy rain and thunderstorms. As Mr. Stan Zontek would remind us “too much water kills more grass than too little in summer.” Heavy rain events bring on saturated soil conditions and oppressive levels of humidity. Scald can result in a total kill of all grass in low areas or in surface water drainage patterns inundated by water in a matter of a few hours after sunshine returns. Wet wilt occurs in the presence of saturated soils and very high levels of humidity, and takes longer to develop. Wet wilt weakens turf and can cause plants to die because transpirational cooling is impaired by closed stomates on leaf and sheath surfaces. Saturated soils also are deprived of oxygen needed by roots to survive. Wet wilt in creeping bentgrass appears as a brownish water-soaked appearance of tissues followed by thinning of the turf. The first management approach to minimize scald and wet wilt is to squeegee as much excess water off putting surfaces before sunshine returns. Fans do an exceptional job cooling and promoting evapotranspiration and should be run 24/7. Any means of promoting air movement, even with portable fans or buffalo blowers, will help alleviate some stress. Syringing can help alleviate wet wilt, but only if water evaporates. If water has not evaporated from the canopy between syringes then syringing should cease as it is likely to contribute to the problem. Avoid mowing and grooming until excess soil water has drained and stress has abated. When it is safe to operate equipment on turf surfaces, solid tine or spike to promote soil aeration, but get it done early in the morning or at dusk.
There are a few precautionary measures you can take to minimize some of the many problems associated with a predicted heavy rain event in summer. First, prepare your in-play areas for the possibility of not being able to mow for several days. This involves applying a plant growth regulator at the highest rate that you feel comfortable using. Solid tine or spike greens and sand-based tees. If soils in your fairways drain well, you may want to solid tine areas prone to puddle. Where soils are compacted and do not drain rapidly, solid tining could result in cupping too much water near the surface and worsen matters. Brown patch and Pythium blight are the two most likely diseases to develop overnight following rain in summer. Thus, apply a tank-mix of fungicides that will protect turf from brown patch and Pythium blight. A constituent of the fungicide tank-mix should contain either Daconil (i.e., chlorothalonil) or Fore (mancozeb) to help prevent or lessen the development of black algal scums as well as brown patch. Once the course is open for play divert carts and other equipment away from soggy fairways and roughs.