Based on Plant Clinic telephone queries and samples, and comments from turf specialists, the common turf diseases on home lawns currently include red thread, rust, and dollar spot. All of these diseases are easy to identify, not requiring the help of a diagnostic lab, microscope, or magic wand. You will find that management options involve many of the same practices.
We discussed red thread in issue No 5 of this newsletter. In the morning dews of the week of August 1, the coral-pink threadlike masses on the grass blades were very noticeable. Pathologists particularly enjoy this sight because the mycelium and sclerotia (resting stage) are so distinctive. The disease does not usually kill plants but will predispose them to other problems. Hosts include Kentucky and annual bluegrasses, fine-leaved fescues, perennial ryegrass, and bentgrass. Look for this disease to cause pinkish patches 2 to 12 inches wide. The patches can merge to cause larger scorched areas with a reddish brown cast. Cut and remove grass clippings until this disease is under control, use a balanced fertilizer program, and water during drought stress. Reseeding with resistant varieties should be done at the end of this month. Red thread is discussed in Report on Plant Diseases No. 413.
Rust is another common turf disease that is currently turning many heads and coloring many white shoes orange. All turfgrasses can be infected with rust fungi, but Kentucky bluegrass, perennial ryegrass, tall fescue, and zoysiagrass tend to be most susceptible. Early symptoms of rust diseases include light yellow flecks on leaves and stems, giving the lawn a yellow cast. The leaf tissue ruptures as these yellow spots and spores of the fungus are produced. The pustules may be yellow, orange, brown, or red. The spores rub off easily on hands, shoes, clothing, and animals. Often the disease is not noticed until you mow the lawn and see that your white shoes are covered with a dusty coating of rust-colored spores. This is usually when we get the telephone calls at the Plant Clinic.
Severely infected turf appears thin and tinted yellow, red, or brown, depending on the fungus and time of year. The turf becomes weakened, unsightly, and more susceptible to injury from environmental stress and other disease pathogens. Grasses growing slowly under stressful environmental conditions are most susceptible to rust, particularly when water, fertility, and soil compaction are inadequate for good growth. Varieties with resistance to susceptibility to rust exist. We could provide a list of these varieties, but that won’t help unless they are available in your garden center. I prefer to look for varieties available for sale and see what disease resistance is advertised with them.
Management measures should target stress areas. Leaf wetness is required for infection, so it is important to water early in the day so the turf can dry before night. Water turf infrequently but to a depth of 6 inches or more at each watering. Avoid frequent, light sprinklings. Fertilize to keep the grass growing about 1 inch per week in summer and early fall droughts. Use balanced fertilizer. Do not apply excessive nitrogen. As the grass grows, it pushes rust-infected leaves outward, making it easy to mow and remove infected blades. Be sure to catch these clippings and remove them from the area, just as you would do with red thread. Mow regularly to remove infected leaf tips, but avoid mowing below the recommended height for the particular turf species. Prune surrounding trees and shrubs to improve light penetration and air circulation around densely shaded areas.
If the lawn is badly infected or the combination of rust and other stress produces a poor lawn and forces a renovation, it is ideally done in mid- to late August. Use a blend of turf cultivars with resistance to rust, as listed in Report on Plant Diseases No. 412 or check with your garden center. Preventive fungicides are available but offer only a temporary solution. Check the usual pest-control handbooks for registered chemicals.
The other turf disease common at this time is dollar spot. This fungal disease infects creeping bentgrass, Kentucky bluegrass, annual bluegrass, and fine-leaf fescues. Even Bermuda grass and zoysia grasses can become infected. The disease appears as roundish, brown spots in the lawn. Initially, spots are silver dollar size (thus the name), and later they may enlarge to as much as 4 to 8 inches in diameter. Merged spots could affect a larger area. The affected area will eventually turn straw colored and will appear sunken in the lawn.
This disease is easy for the layman to identify. A quick and rather good diagnostic guide involves the appearance of the leaf lesions (dead areas on the leaf). Look for these on plants at the edge of the sunken areas. The lesions girdle the blade, may be up to 1 inch long, and are usually bleached white to light tan, with a dark-brown, reddish-brown, or purplish border. When dew is present on the blades of grass on overcast days or early in the morning, a white cobweb-like growth of mycelia may be seen on infected plants. The disease appears in warm (60°F to 85°F), wet, and humid weather, especially in lawns that are low in nitrogen. Control measures include maintaining balanced fertility, avoiding late-afternoon or evening watering, providing good air circulation in the area by pruning surrounding plants, providing adequate surface drainage, mowing at the maximal height, and using resistant cultivars of grass. Chemical options can be used on a preventive basis but are generally used only on golf courses or high visibility areas. Refer to the Illinois Homeowners’ Guide to Pest Management Handbook or the Illinois Commercial Landscape & Turfgrass Pest Management Handbook 2000 for chemical options. Also refer to Report on Plant Diseases No. 407 for details on the disease, pathogen, and management options.