Rusts (Puccinia Species)
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 enhancement of 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.
Several cultural practices will help control rust on lawns.