(fungus - Rhizoctonia solani): The name, brown patch, is not very descriptive of the varied symptom expression caused by Rhizoctonia spp. on turfgrass. Symptoms differ on cool- and warm-season grasses and vary depending on environmental conditions and cultural practices.
Turfgrass affected by brown patch generally will exhibit circular or irregular patches of light brown, thinned grass. On cool-season grasses (bent, rye and fescue) during periods of warm, humid weather, a darkened border or smoke ring may develop at the outer margin of the patches. The smoke-ring symptom is not reliable for diagnosis.
Symptoms on warm-season grasses such as bermudagrass or St. Augustinegrass include circular to irregular patches of blighted turf. Patches up to several yards in diameter commonly develop in the fall, winter and spring when these grasses are approaching or emerging from dormancy, evening temperatures are below 68 oF, and rainfall usually increases. Active infections are noticeable by yellow leaves at the edges of patches. Leaf sheaths become rotted, and a gentle tug on the leaf blade easily separates the leaf from the runner. Brown patch usually does not discolored roots. Disease develops most rapidly when air temperatures are between 75 and 85 oF and wet conditions are present and generally subsides when air temperatures rise above 90 oF.
Management: Water only as needed and early in the day to remove dew and allow the grass to dry quickly. Avoid over fertilization in spring and fall. Improve the turfgrass root system with good drainage and aeration to reduce damage caused by brown patch. Fungicide are most effective when used on a preventive basis.
Grey Leaf Spot
Gray Leaf Spot
(fungus - Pyricularia grisea): Gray leaf spot develops rapidly with abundant moisture and warm temperatures on St. Augustinegrass . It is especially troublesome in shaded areas that remain damp for some time. Under these conditions, the disease causes serious thinning of the turf. Leaf spots first appear as tiny brown to ash- colored spots with purple to brown margins that enlarge and become diamond-shaped. In severe cases, lesions develop on stems and spikes and the leaves wither and die. Turfgrass may have a burned or scorched appearance resulting from death or spotting of the leaf blades.
Management: Avoid application of soluble nitrogen fertilizers on moderately shaded lawns during summer months. Apply water early in the morning only when water is needed. Avoid evening waterings which keep the leaf surface wet for long periods. Catch and remove grass clippings where gray leaf spot is a problem. Several fungicides are recommended for gray leaf spot control.
(fungi - Gaeumannomyces graminis var. graminis or avenae )Take-all root rot fungus is active in fall and winter when there is abundant moisture and moderate temperatures. However, symptoms are often expressed in late spring or early summer when affected turfgrass first experiences the stressful effects of high temperature and dry weather . This disease has the ability to destroy large sections of turfgrass if left uncontrolled.
The first symptom is often yellowing of the leaves which eventually die. Turf becomes thin as roots, nodes and stolons become infected and plants die. Unlike brown patch, leaves of take-all infected plants do not easily separate from the plant when pulled. Roots become rotted so damaged stolons are easily pulled from the ground, similar to white grub damage. Regrowth of grass into affected areas is often slow and unsuccessful.
Management: Controlling take-all is not easy and both cultural and chemical methods should be considered. Good surface and subsurface drainage is important. Irrigate only when required, and infrequent but thorough water is preferred to frequent shallow watering. Verticutting to remove thatch also helps. Aerification alleviates soil compactions and promotes a deeper, more vigorous root system. Balanced fertility is important. If possible, adjust the soil pH in the upper root zone to a range of pH 6.0 to 6.5. Preventive fungicides are best applied in the fall since the fungus is thought to be most active at that time.