bpm382 – posted 17 March 2011 17:37 I planted a new back yard lawn last fall. We’ve had record snowfall this winter. Now that the snow is gone, I have hundreds of perfect circles of diseased grass in my backyard.…
Pests of turfgrass include insects, fungi as agents of disease, nematodes, and weeds. Less common are virus diseases of turfgrass, vertebrate pests such as moles, and other arthropod pests such as eriophyid mites which are often lumped with insects. Pests occur because of three things, an egg or inoculum source of the pest, a conducive environment, and a susceptible host. Pests can be managed using synthetic pesticides and biological control and other gentler methods. Non-organism causes of disease such as drought, nutritional deficiency, and air pollution can cause symptoms similar to symptoms of pests.
Common insects attacking lawns and golf courses are southern chinch bug, Blissus insularis, in St. Augustinegrass; mole crickets in several grasses such as bermudagrass; armyworm, tropical sod webworm, and other grass caterpillars in all species of warm-season and cool-season turfgrasses; white grubs or chafers; and billbugs. Common nematodes affecting roots of grasses (and indirectly the whole plants) are sting, lance, and rootknot nematodes. Fungus diseases are Helminthosporium spp., Pythium spp., Rhizoctonia spp., and Gaeumannomyces graminis which causes bermudagrass decline and take-all root-rot disease of St. Augustinegrass.
Diagnosing pest problems in turf requires knowing signs and symptoms. Symptoms are the abnormal condition of the turfgrass, such as yellowing, browning, or spotting of leaves. Signs are more specific than symptoms. A fungus disease can create symptoms such as yellow leaves, and the signs are the fungus mycelia on the dewy grass. Caterpillar symptoms can be skeletonizing of leaves, and signs can be frass, the block-like excreta. While signs are like the “smoking gun” in a murder case, symptoms are circumstantial evidence. Symptoms are very interesting to ponder because their shape can narrow down the probable causes. For example, a turf area showing strong rectilinear patterns was probably harmed by a human-associated factor. Insects and fungi do not normally cause damage in straight lines or make right angle turns.