Rust
Rust
Rust diseases, caused primarily by Puccinia spp., occur on all commonly grown turf-grasses. Like the mildews and smuts, these fungi are highly specialized as to host preference. Two of the more common turfgrass rusts are P. graminis, causing stem rust on Kentucky bluegrass, and P. coronate, causing crown rust on ryegrass and tall fescue. The severity of outbreaks varies from year to year. Kentucky bluegrass, perennial ryegrass, tall fescue, and zoysiagrass are the turfs most affected.
Rust usually occurs from mid to late summer until early October following hot, dry periods when grass growth has slowed. It becomes severe when lack of water, low fertility, or soil compaction reduce turf growth. Warm days and moderate night temperatures along with long dew periods or night watering create optimal environmental conditions for rust. For infection to occur, the turf must remain wet continuously for six to eight hours. In mild winters or in mild climates, rust can survive in infected plants. However, in the central and northern plains it overwinters in the south and spores are carried north by wings during the growing season. Variable survival of the fungus is one reason for the sporadic nature of the disease and the late season buildup of rust.
Symptoms
Heavily rusted turfs appear yellow or orange when seen from a distance. Clouds of orange spores quickly discolor shoes, mowers, grass catchers, and pant legs. Close examination of rusted leaf blades reveals the presence of orange to brick-red pustules. Spores within these pustules rub off easily when touched. Each rust pustule produces a vast number of spores, each of which is capable of infecting a grass blade. New infections occur about every seven to ten days. Under ideal conditions, turf can become heavily rusted about 40 days after initial infection. Heavily infected turf is weak and thin, making them more susceptible to winter injury and other environmental stresses.
Treatment
Management begins with the use of improved rust-resistant turfgrass cultivars. Maintaining the turf in a vigorous but not lush condition by proper fertilization, early morning watering, and aerating to alleviate compaction are recommended to prevent injury. Regular mowing also reduces the risk of severe rusting in late summer and autumn. Fungicides may be needed to control rust on sod fields and on other turfs in certain years with the initial application in early July followed by one or two additional treatments at three-week intervals. However, under most situations good management will be sufficient to prevent sever rusting in late summer.
Reference
J. E. Watkins. (1997). Diseases of Cool Season Turfgrass. In F. Baxendale, Ph.D., & R. Gaussoin, Ph.D., Integrated Turfgrass Management for the Northern Great Plains (pp. 131-133). Location: Nebraska