Rusts are considered a minor disease on turfgrass in North America. Most cool season grasses are susceptible to rusts. Perennial ryegrass is the most susceptible and Kentucky bluegrass is slightly less susceptible. Rusts generally appear on lawns in late summer and fall. The disease is most active during conditions of low light intensity (cloudy overcast weather) and temperatures between 72-77°F (22-25°C) with high humidity. After infection, symptoms and stress caused to the turf is enhanced with temperatures 78-95°F (26-35°C). Alternating weather patterns changing in cycles from cool wet weather to hot dry weather can also create suitable conditions for the disease. Rusts survive on living and dead leaf tissue and in the thatch layer of turfgrass and/or on alternate hosts (such as barberry or other ornamental plants) when they are not affecting the grass blades. Only when weather conditions become suitable do they begin to cause a concern on the lawn.
Initially, rust symptoms appear as light yellow flecks on the leaves and sheaths. Reddish orange (rust colored) spores then develop in large numbers on the leaves of the grass plants. In most cases the spores only attack the leaf blades causing wilting and thinning of the grass. Severe cases of rust can significantly damage turfgrasses. One sure way to identify this disease is to walk through the infected area and look at your shoes – if they look rusty, you will know your lawn has rust disease.
Several cultural practices will help control rust on lawns.
- Increase mowing height and frequency.
- Aerate to improve drainage and encourage air circulation.
- Reduce periods of leaf wetness.
- Provide an application of fertilizer to help promote recovery.
- Avoid drought stress by watering deeply and infrequently.