Rusts are often first noticed when you walk through the lawn, especially with white running shoes. You find that your shoes have turned orange. This orange-red dust is composed of the many spores that produce this disease. At this time, you may then notice the rusty appearance of the lawn. The spores are carried by the wind to other lawns. If they land on grass blades with sufficient moisture, a new infection is started.
Rusts can affect all turf grasses but perennial ryegrass and Kentucky bluegrass are the most susceptible. Infection occurs with 4-8 hours of 22-25oC temperatures, cloudy weather and high humidity. Rust is most common during July and August but can occur from July to October.
There will be small chlorotic flecks on either the upper or lower leaf surface, followed by reddish brown pustules containing spores. The spores are easily rubbed off. Severe cases may result in yellowing and wilt. Where the turf is killed, the pustules become brown-black on the dead tissue.
Control: Rusts are a minor disease in Ontario. Mowing and managing fertility will usually control the disease and prevent damage. Provide a balanced Nitrogen feeding to the lawn. This will avoid nutrient stress and improve leaf growth. Either too much or too little Nitrogen can favour rust development. Reduce shade and improve air circulation. Use resistant varieties if possible. Water infrequently but thoroughly early in the day.
When the disease is present, increase the mowing height and frequency. These 2 practices will encourage faster growth and will reduce the disease incidence and severity by allowing the grass to grow faster than the disease.
Our recommendations also include an aeration to improve the general health of the lawn. Consider adding a Winter fertilizer to your program to improve the lawn's nutrition.