Rust Diseases of Turfgrasses

Ned A. Tisserat
   Extension Specialist, Plant Pathology

Symptoms

Rust occurs to some extent on all turfgrasses grown in Kansas; however, this disease is generally most severe on susceptible cultivars of Kentucky bluegrass, tall fescue, perennial ryegrass, and zoysiagrass. Rust usually appears in late August to early September and continues through the fall months, but it may also develop at other times of the year depending on weather conditions and turfgrass species. Disease severity may vary dramatically from one year to another.

From a distance, rust-infected turf appears dull yellow or light brown. Individual plants may die, and the turf becomes noticeably thin. The disease tends to be more severe in partially shaded areas, such as under trees or along fences.

Figure 1. Rust on Kentucky bluegrass.

Figure 2. Rust on zoysiagrass.

Diseased plants initially develop light-yellow flecks on the leaves. As the spots enlarge, the surfaces of the leaves rupture, exposing masses of powdery, brick red spores of the fungus. The powdery material rubs off easily on your fingers, shoes or clothing. Rust-colored spores of the fungus are diagnostic of this disease. Continuous heavy infection causes many grass blades to turn yellow, wither, and die. Severely rusted lawns may winterkill.

Figure 3. Rust on perennial ryegrass (courtesy D. Settle).

Conditions for Disease Development

The rust fungi (Puccinia spp.) overwinter in infected plants or are reintroduced into lawns each summer by wind-blown spores. Infection of leaf blades is favored by moderate temperatures (68 to 85 degrees F) and extended wet periods. Once infection occurs, slightly higher temperatures favor symptom development. Turfgrasses under stress (drought, shading, close mowing heights and high temperatures) are most likely to be seriously damaged by the disease.

Disease Management

Turfgrass provided with optimal levels of fertilizer and water is less likely to be severely damaged by rust. Avoid night watering which increases the length of time the leaf blades remain wet. Regular mowing, which severs infected leaf tips from the plant, will help reduce inoculum levels. The best strategy is to mow frequently at a height not less than what is recommended for the turfgrass. Avoid close mowing or scalping of the turf.

Several fungicides are labeled for the control of rust. In general these products work best when applied early in disease development. For Kentucky bluegrass, this first application is normally in late August or early September.

The decision to use fungicides is often difficult because applications need to be made relatively early in rust development. Since the rust epidemic is dependent on weather, it is hard to determine if early fungicide sprays are warranted. In most years rust doesn't reach damaging levels before the turfgrass enters winter dormancy. Therefore, fungicides are not routinely used for rust control in home or commercial landscapes.

good

7-21 days

Heritage

good

7-21 days

Chlorostar, Daconil, Echo, Manicure, Thalonil, others

good

7-14 days

Fore, Dithane, Formec, Mancozeb, Protect

Good-excellent

14 days

Eagle

Good-excellent

14 days

Banner

good

7-21 days

Compass

good-excellent

14-28 days

Accost, Bayleton, Fungicide VII, Fungi-Fighter, others

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Web updated 9/01/06
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