It's the humidity. Actually, it's both. As I write this, the weather station says that it is 87 degrees with a heat index of 98. The dew point is 77 and the relative humidity is 72 percent. Did I mention it is 9:18 AM? When I woke up, it was 82.
These conditions are much worse than hot and dry. One of the biggest fears of golf course superintendents is of a Pythium outbreak. Pythium is a fungus, Pythium graminicola and other Pythuim species, that appears suddenly during hot, humid weather. It requires night-time low temperatures of over 68 degrees and more than 10 hours a day of leaf wetness for several consecutive days. The symptoms are greasy, circular spots, 1 to 2 inches in diameter that rapidly enlarge in size. It can also form fluffy white masses of mycelium (the fruiting bodies of a fungus) which can coalesce to form large, irregular patches of dead turf. This mycelium can be transported by vehicles, mowers or water.
Given the speed with which a pythium outbreak can become large patches of dead turf, we have sprayed the greens and tees with a fungicide that will prevent pythium. We will try to not spray the fairways, given the amount of area that would be involved. Instead, we have cut back on the irrigation on the fairways in order to decrease the humidity in the turf canopy. This may result in some brown areas on the fairways, but will also save us from having to spray a fungicide on 25 acres of turf. This is not only better for the environment, but also helps our budget.
One of the reasons we can contemplate cutting the irrigation is because of the high humidity. According to our weather station, the evapotranspiration (ET) rate yesterday was 0.14 inches. This is an estimate of the amount of water that the turf will use during a day. To compare, the ET rate on Friday, July 8th was 0.24 inches, even though the high temperature that day was 84 degrees. The relative humidity was down near 32%.
Hopefully, this weather will break soon. WeatherUnderground is forcasting the low temperature on Monday to be 61 degrees. Keep your fingers crossed.