Smut

Disease

Striped Smut

Ustilago striiformis, Urocystis agropyri


The smut diseases are important on many Kentucky bluegrass cultivars and higher cut turfgrass. Individual infected plants may be found in a stand of turf, or large patches of infected plants may form. Infected plants tend to not grow as profusely as healthy plants, with stunted growth and stiff, erect leaves rather than relaxed spreading leaves. Light yellow blades of grass are evident during the initial phase of the disease, and as symptoms advance, leaf blades begin to curl and show black stripes running the length of the blade. Older infected blades appear twisted, curled, and shredded from the tips down.

The fungus overwinters as mycelia in infected plants, and infection is thought to occur in the cool wet weather of the spring and fall. Symptoms are most commonly seen in the spring and fall when the temperature is below 70° F (21.1° C), and gradually disappear as the weather becomes warmer. Extensive turf loss occurs during hot, dry summer weather, when grass is under heat or drought stress.

  • Crops Affected: Turfgrass

    Damage

    The location of this disease is home lawns and golf courses. General symptoms are patches, streaks, wilting, and irregular coloring. Foliar symptoms are browning, and water-soaked. This can occur during the months of March, April, May, June, July, August, September, October, and November. Hosts of the disease are Kentucky Bluegrass, Creeping Bentgrass, and Colonial Bent.

    Management

    Keeping nitrogen applications to a minimum during the summer months with no more than 0.5 lb of nitrogen per 1000 ft2 (0.25 kg per 100 m2) can aide in alleviating symptoms. Turf infected with stripe smut should not be allowed to dry out. Healthy plants become dormant when dry and will recover when irrigated, but an infected lawn will die no matter the amount of water applied.

    Several Kentucky bluegrass cultivars are resistant to stripe smut (more>> National Turfgrass Evaluation Program), but this resistance can be overcome. Blends of three or four Kentucky bluegrass cultivars are recommended because of this.

    Stripe smut is a systemic (internal) disease that must be managed by systemic fungicides. The DMI fungicides, fenarimol, triadimefon, and propiconazole, are the most effective in managing stripe smut. Monthly applications throughout the growing season will manage the disease. Renovation of an infested home lawn with improved Kentucky bluegrass cultivars may be more cost effective than a fungicide regimen for most homeowners.