Area residents have been contacting ISU Extension and Outreach offices with questions about why their lawns are turning yellowish-orange or orange in color. This is most likely a result of a fungal disease called rust. Rust initially appears in diseased plants as yellow spots on leaves. Later these spots become larger and the fungus comes through the outer surface of the leaves as powdery orange spores.
Rust often shows up in midsummer and more frequently when the growth of the grass has been slowed by stresses such as drought, low fertility, compaction or mowing too closely. Optimum conditions for rust development are when temperatures are 68-85OF and when leaves stay wet for an extended time period. Rust spreads through the air, water, lawn equipment, pant legs and shoes.
To control rust in lawns, certain cultural practices can be used that will promote a healthy lawn. Keeping lawns mowed regularly to remove the infected tips will reduce the amount of fungi present. Recommended mowing heights for most lawns, in midsummer, are 3-3 ½ inches. Remember it is best to never remove more than one third of the height of the plant when mowing. Lawns should be watered early in the day to ensure that the plants are dry by evening. Also, avoid frequent light waterings. Test lawns for soil fertility and apply fertilizer at levels recommended by the soil test results. This will ensure proper levels of nutrients are available to lawns. Check that the thatch layer, layer of dead grass material on the lawn’s soil surface, is no more than ½ an inch in thickness. When seeding, choose a grass blend with one or more disease resistant cultivars. Fungicides are rarely suggested for treatment of rust and most rust fungi that effect lawns do not survive Iowa winters.
Additional information on this and other plant problems can be found by contacting your local Extension and Outreach office. Contact information for each county office can be found by visiting www.extension.iastate.edu.
ISU Extension and Outreach is part of an educational network supported by Iowa State University, local county governments, and the United States Department of Agriculture. ISUEO works to increase learning opportunities for citizens of Iowa by providing unbiased, research-based information that will improve quality of life. Its programs are available to all without regard to race, color, age, religion, national origin, sexual orientation, gender identity, genetic information, sex, marital status, disability, or status as a U.S. veteran.