Fusarium blight is caused by the widespread fungi Fusarium roseum
and F. tricinctum. The disease is most troublesome on cool season
grasses such as bentgrass, bluegrass and tall fescue, but occasionally attacks
the warm season grasses as well. The disease is most serious during hot,
humid conditions when the turfgrasses are under drought stress.
Symptoms. Initially, affected grasses display light green patches 2- to 6-inches in diameter. The shape of the affected areas may appear as circular patches, elongated streaks or crescents. At high temperatures, the patches quickly change from light green to reddish brown, then tan and finally to straw-colored. The most characteristic symptom at this stage is a doughnut-shaped area up to 3 feet in diameter with healthy grass in the center giving a "frog-eye" pattern to the diseased area. When conditions of high temperature and high humidity persist for an extended time, these diseased areas become numerous and may overlap. As a result, large areas of turf may appear blighted. As the disease progresses, grass dies as the crown and root tissues are destroyed.
On individual leaves, dark green blotches envelope the full width of the leaf blade. As the disease progresses these symptoms extend from the cut leaf tip to the base. The color changes from dark green to reddish-brown and finally to a dull tan.
Disease Cycle. The fungi that cause fusarium blight survive the winter in the thatch layer and on infected grass roots, crowns and rhizomes. As temperatures increase above 70° spore production begins. When air temperatures are between 75° and 90° and humidity is high spore production becomes profuse and affected grass may die in 4 to 7 days after the first symptoms appear. The fungi show little activity when air temperatures are below 70°, or when humidity is very low.
High nitrogen levels favor fusarium blight because of the greater accumulations of thatch. Also, excessive watering creates conditions more favorable for the fungi.
Control. In bluegrass areas, fusarium blight can be prevented by planting mixtures of bluegrass with perennial ryegrass. Otherwise, a fungicide together with a program to control thatch is essential for effective control of fusarium blight. Bayleton, Chipco 26019, and Rubigan are labelled for control of fusarium blight.