What Causes Rust on Grass?

Grasses, like all other flora, are not immune from disease, mold and fungal infection and insect interference. A vital part of lawn maintenance is to learn the telltale signs of these afflictions so that you can control them before they diminish the look or health of your grass.

Rust gets its name from its dirty orange color, but is actually a fungal infection characterized by the appearance of rust colored powder intermittently scattered across a lawn. The powder is actually the result of fungal sporulation after the fungus has taken hold on the inside of the grass's vasculature. If you walk across or use lawn equipment on grass that's been infected with rust, you will probably notice it coming off and sticking to your shoes and the equipment.

Rust diseases in grasses are caused by a nitrogen deficiency in the soil. This deficiency, combined with insufficient moisture, slows down the growth of the grass, thereby making it more susceptible to fungal infection. Weather conditions can influence nitrogen levels in soil. Heavy rains wash out available nitrogen in the soil as do abrupt changes from warm, humid weather to dry heat. Certain grass species, such as Kentucky bluegrass, perennial ryegrass, and tall fescue, are more prone to rust infection than other species. The infection can also spread easily since fungal spores can be carried by wind, rain, people, clothes or lawn equipment.

Since nitrogen deficiency is the chief cause of rust infections, proper lawn maintenance techniques are probably the most effective preventative measures. Test your lawn soil for nutrient levels -- not just nitrogen but phosphorous and potassium as well -- and fertilize accordingly to supplement the needed nutrients. Lawn grasses typically respond well to September fertilizer applications. Keeping your lawn regularly mowed and removing grass clippings from the lawn after mowing can further inhibit rust infections.

Rust, under most circumstances, will not kill you lawn; it is considered more a cosmetic than a health issue. Still, if lawn appearance if important to you, consider buying a grass species or species cultivar that is naturally resistant to rust infections. Fungicides usually are not necessary to control rust except in the most extreme of infections.