Rust diseases are found throughout the U.S. on most species of grasses.
Bluegrass, ryegrass and zoysiagrass are most commonly affected. Rust diseases
are favored by warm and humid conditions and develop most frequently on
grasses subject to stress-droughty conditions, low nitrogen fertility and
shade. Low mowing heights, particularly on Kentucky bluegrass, also increase
the susceptibility of grasses to rust.
Symptoms. The disease first appears on grass leaves as small orange to reddish-brown flecks that enlarge to form raised pustules on leaves and stems. Individual pustules are usually oval or elongated and contain a powdery mass of orange to reddish-brown spores. As the pustules mature they turn brown to black. Heavily infested turf becomes thin with an overall yellow-orange to reddish-brown color. Infected leaves turn yellow, wither and die.
In southern states, ryegrasses are highly susceptible to rust in the spring, particularly where nitrogen fertility is low. Zoysiagrasses are most often affected by rust in the fall as the growth rate of grass slows and environmental conditions favor disease development.
Control. Cultural practices which improve the vigor of the turf help prevent rust. To reduce the incidence of rust, keep nitrogen levels adequate for turf growth, avoid moisture stress or overwatering and adjust mowing heights according to the grass needs. In the case of Kentucky bluegrass and perennial ryegrass, use varieties that have good resistance to rust where the disease is a problem.
Where these measures fail to provide adequate control of rust diseases, fungicides are available for its control. Banner, Bayleton, Sentinel, Daconil, and Acti-dione RZ are some of the fungicides labeled for the control of rust on turfgrasses.