Another strange weather year is upon us. Dry and windy weather greeted early June, followed by one deluge after another in mid-to-late June and early July. It could be the “perfect storm” for diseases throughout the mid-Atlantic region and in all grasses if this weather trend continues. I have seen little brown patch (Rhizoctonia solani) activity in Kentucky bluegrass monostands, but with the combination of numerous rain storms and high humidity, this disease has taken off. It is mostly a problem in areas with shade and poor air circulation. Blighted turf appears brown in color and in circular patches or may be diffuse in mixed stands with tall fescue. The lesions on Kentucky bluegrass leaves are remarkably similar to dollar spot. Lesions on bluegrass leaves are hour-glass- shaped and there is the familiar brownish margins bordering green and infected tissue. Instead of lesions being bleached-white, however, Rhizoctonia lesions have a tannish-white color. Some oval-shaped lesions also may be found. There is no foliar mycelium nor smoke rings in bluegrass. When blighted tissue is incubated, no foliar mycelium can be seen with the naked eye. However, when blighted leaves are placed under a microscope at about 100x power, small hyphal strands of brownish mycelium bearing the familiar right angle branching of Rhizoctonia spp. become evident. Brown patch, a chronic summer disease of tall fescue, also is rampant in the region. In tall fescue, smoke rings and foliar mycelium are common during morning hours. The presence of some Kentucky bluegrass in tall fescue usually masks the disease and limits blighting. While turf would be expected to recover, the brown-colored foliage remains evident for long periods after the disease subsides, which most homeowners find highly objectionable. Preventive control is most effective, but even curative applications of fungicides quickly limit significant damage if applied early in an epidemic. Some homeowners are willing to pay the cost of a fungicide treatment to minimize injury.
Pythium blight (several Pythium spp.) is a growing problem in tall fescue. Pythium blight is especially common in shaded or fenced-in areas where air circulation is restricted and in surface water drainage patterns. Periods of heavy rain and/or thunderstorms, as well as hot and very humid weather, usually coincide with an outbreak. This disease problem in tall fescue is due in-part to breeding finer textured and more dense cultivars. It could be, however, that newer cultivars are simply more susceptible to this disease, but are not identified in university trials, which usually are conducted in open areas and in full sun. Pythium blight is mostly found in tall fescue lawns, however, in mixed stands with Kentucky bluegrass you may find blighting in both species. Pythium blight first appears as orange or bronzed-colored spots, which mimic the kind of damage that comes with gasoline spills or dog urine damage. Spots increase to about 6” in diameter and coalesce quickly. In early morning hours, you may see mycelium, which appears grayish-white and “frothy or cottony” within the canopy. Blighted leaves collapse and mat and have a “soapy” feel. Once the disease appears, quick fungicide action is required to prevent severe damage to lawns.