Rust on turfgrasses

By John Fulton

[August 27, 2008]  It may seem an odd time of year to be reading about rust on turfgrasses, but Logan County has had an outbreak the past two weeks. Turf rusts generally appear in cooler temperatures, and 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 (such as big swings in temperature and moisture) 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. It may be helpful 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 late August or early September. Use a blend of turf cultivars with resistance to rust, but beware that what was once resistant may no longer be. The rust fungi keep evolving and eventually defeat the old-line resistance.

Preventive fungicides are available, but they offer only a temporary solution. The fungicide treatments tend to be costly and time-consuming. Daconil is the most common fungicide used on turf, but following the management practices will produce better long-term results.

To offer a ray of hope, diseases must have ideal conditions to develop. Just wait for a major weather change and the rust will go away. At least for a while.

[By JOHN FULTON, University of Illinois Extension, Logan County]