Rust

Disease

Puccinia striiformis, P. graminis, P. coronata

Photos

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Rust diseases are characterized by yellow to dark brown urediospore infestations that, from a distance, make turf stands appear orange or yellow. These rust-colored urediospores protrude through the plants epidermis causing spots that elongate parallel to the leaf or stem axis. When rust is severe, areas of infected turf appear thin, weak and are have a red, brown, or yellow tint. Heavily infected plants may wither or die from excessive loss of moisture from rusted leaves.

Rust populations sporulate at a variety of temperatures, but generally optimal temperatures for epidemics are between 68° and 86° F (20-30° C). In warmer regions, the fungus can overwinter as mycelium or active spores in infected plants. Spores land on susceptible hosts in the spring, germinate, and infect plants. Initial sporulation is followed in many cases by successive rounds of sporulation, leading to exponential production of inoculum. Rust diseases are typically most severe in slow growing grasses that are under stress. Parameters optimal for infection include low light, high dew points, and moderate temperatures.

  • Crops Affected: turf

    Damage

    The location of this disease is home lawns and golf courses. General symptoms are irregular coloring. Foliar symptoms are dusting and turning orange. This can occur during the months of May, June, July, August, September, and October. Hosts of the disease are Kentucky Bluegrass, Perennial Ryegrass, and Tall Fescue.

    Management

    Adequate nitrogen fertility and proper irrigation can often eliminate rust as a major problem. If the turf is mowed once per week, the disease severity tends to diminish as well. The removal of clippings that are infected with spores can serve as a means of reducing the spread of inoculum. Improving air movement as well as light penetration by pruning trees or shrubs can help as well. Areas where turf grows slowly and where prolonged, cool, wet weather is common, may have to resort to chemical management options.

    Many grass cultivars show at least some level of resistance to rust diseases. Blends of cultivars are recommended as monostands tend to be highly susceptible to epidemics.

    Chemical management of rusts may be necessary on slow-growing turf. Chemical management is also needed on grasses grown for seed production, because they are typically not mowed. The DMI fungicides among others, provide adequate management of the various rust fungi.

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