Summer means brown patch disease season in turfgrasses. The following is more information.
Brown patch disease will be coming active in Delaware soon, especially in tall fescue. Warm, humid weather will promote brown patch activity on cool- season turfgrasses. Perennial ryegrass is probably the most susceptible host; creeping bentgrass and tall fescue are both relatively susceptible. Sometimes we see brown patch on Kentucky bluegrass, as well.
On all grasses, affected patches are often somewhat circular and can range from several inches to two or more feet in size. On tall fescue and Kentucky bluegrass, leaves exhibit tan, irregular lesions with a thin, brown border. On creeping bentgrass and perennial ryegrass, a ring of olive- green leaf blades appears on the outside margin of the patch; these blighted leaf blades dry to a tan color. On humid mornings, the mycelium of the fungus often appears as a sparse, very light tan webbing in the lower canopy. This can be best seen with a hand lens. In some situations on perennial ryegrass, the mycelium can be quite dense, cottony, and fluffy, and grow all over the leaf blades. In this condition, it can look quite a bit like Pythium cottony blight. Since different fungicides are used against Pythium cottony blight and Rhizoctonia brown patch, knowing the identity of the disease can be quite important from a management standpoint. Laboratory diagnosis is the best option if a case of perennial ryegrass has dense mycelium that looks like Pythium blight.
Management: During the next 8-10 weeks or so, be careful with postemergence herbicides, some of which have been shown to increase brown patch activity on cool-season turfgrasses.
Tall fescue. Generally brown patch can be managed through cultural means in established tall fescue lawns. However, recent seedings of tall fescue often can suffer severe outbreaks of the disease during humid weather in summer months. These should be monitored carefully and treated with fungicide if necessary. Once these swards make it through their first summer and are well-established, they often do not need fungicide treatment to maintain sward density, although fungicides do improve overall greenness during summer. Be aware that products containing chlorothalonil and iprodione are no longer labeled for use on home lawns.
Kentucky bluegrass. Although brown patch may be active in adapted varieties of Kentucky bluegrass, brown patch rarely develops aggressively enough on this host to justify fungicide treatment.
Perennial ryegrass and creeping bentgrass. High- maintenance perennial ryegrass and creeping bentgrass swards should have preventive fungicide applications on at this point, and putting greens should continue to receive preventive applications for brown patch control through August (and possibly later, depending on weather).
There is a wide selection of fungicides with very good activity for brown patch control. See the Extension publication PPA-1, Chemical Control of Turfgrass Diseases (http://www.ca.uky.edu/agc/pubs/ppa/ppa1/ppa1.pdf) for options.
Adapted from "Brown Patch Activity" By Paul Vincelli in the current edition of the Kentucky Pest News http://www.uky.edu/Ag/kpn/kpn_09/pn_090630.html