It may seem an odd time of year to be reading about rust on turfgrasses, but we have reports of many such cases in the midsection of the state. Turf rusts generally appear in cooler temperatures and, if you force yourself to remember, we recently experienced a week of cool days with low humidity and very cool nights. The result was a nice crop of rust in the lawn.
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 at these yellow spots, and spores of the fungus are produced. The pustules may be yellow, orange, brown, or red. The spores rub off very easily on hands, shoes, clothing, and animals. Often, the disease goes unnoticed until you mow the lawn and see that your white shoes are covered with a dusty coating of rust-colored spores.
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. There are also varieties with resistance and susceptibility to rust.
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 and 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. 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. Preventive fungicides are available, but they offer only a temporary solution. Check the usual pest control handbooks for registered chemicals.