Disease Identification

• Rust is a fungal disease that is caused by numerous fungi, most frequently by those in the genus Puccinia. The disease affects all warm and cool season grasses equally. Among the warm season grasses, zoysiagrass is the most severely damaged by rust, according to the Alabama Cooperative Extension.
  
  

Recommended Fungicides

• Products containing the fungicides strobilurin, propiconazole, azoxystrobin, iprodione and myclobutanil are recommended as treatment for rust disease. However, since the disease is primarily caused by poor cultural management, the correction of these conditions should be the main treatment strategy. Chemicals are recommended only when symptoms are not alleviated by improving growth conditions, suggests the Purdue Cooperative Extension.
  
  

Application Suggestions

• Start the use of fungicides shortly after the appearance of disease symptoms. Continue treating the lawn until the adverse cultural conditions favoring disease are eliminated or fixed. Lawns that are severely damaged by the fungus will take a long time to recover and signs of healthy growth will not appear very quickly. Reapply the chemicals every two to four weeks until symptoms are gone.
  
  

Cultural Conditions Favoring Disease

• Rust disease is more common on zoysiagrass that is suffering from drought stress and is growing in poorly fertile soil. Lawns that are insufficiently fertilized with nitrogen are also more prone to fungal growth. Zoysiagrass that is not getting enough air circulation and is planted in shade, causing an excessive buildup of dew on grass, often gets more severely affected with rust. The disease usually appears on zoysiagrass during May with another recurrence in July.