AMES, Iowa — There are challenges to keeping Iowa lawns green throughout the summer. This week Iowa State University Extension and Outreach horticulturists address issues that add undesirable color to lawns – specifically yellowish orange and brown.
My lawn has started to turn brown because of recent dry weather. Will the grass die if I don’t water it?
Dormancy is a natural survival mechanism for Kentucky bluegrass and other cool-season grasses. During extended dry periods, turfgrass foliage will cease growth and turn brown. While the foliage is dead, the turfgrass crowns and roots remain alive. Generally, turfgrass can remain dormant for four to six weeks without suffering significant damage.
Cool-season grasses are at risk of dying if dormant for more than six weeks. To insure survival of dormant grass, it’s best to water lawns that have been dormant for six weeks. Apply 1 to 1½ inches of water in a single application. Water again seven days later. The grass should begin to green up after the second application.
Several areas in my lawn have turned yellowish orange. When I walk across these areas, an orange dust gets on my shoes. What is the problem?
The yellowish orange color is likely due to rust. Rust is a fungal disease caused by several species of Puccinia. All turfgrass species are susceptible to rust. However, it is most commonly seen on perennial ryegrass and Kentucky bluegrass.
From a distance, rust infected turf has a yellowish orange color. Close examination of rust-infected grass blades reveals numerous yellow-orange pustules. Rust can be easily diagnosed by walking across the lawn. As you walk across the lawn, the bright orange spores of the rust fungus rub off onto your shoes.
Rust most often occurs in mid- to late summer. Slowly growing grass is most susceptible to rust infections. Poor turf growth may be due to drought, high temperatures, low fertility or a low mowing height. Warm days, moderate night temperatures, high humidity and heavy dews provide favorable conditions for rust infections.
Rust is annoying, but it rarely kills established lawns. The damage is mainly cosmetic. New spring-seeded lawns are most likely to be seriously damaged by rust.
Rust usually fades away (by itself) when the grass begins growing more rapidly with favorable weather conditions. Gardeners can promote turfgrass vigor by fertilizing in September and watering deeply once a week during dry periods. Water in the morning. Morning irrigation allows the grass blades to quickly dry, thereby discouraging rust infections. Mow the lawn frequently. In most situations, fungicide applications are not necessary.
When establishing a lawn from seed, select a high quality seed mix. Inexpensive, poor quality seed mixes often contain grass cultivars that are highly susceptible to rust.