Control Plant Diseases 
For Better Farming And Better Living Mimeo BP 7-1

MELTING-OUT OF BLUEGRASS LAWNS

One of the most widespread diseases of bluegrass lawns in Indiana is a condition known as 'melting-out." This disease results in noticeably thinned or weak areas in the lawn, vary-ing in size from a few inches in diameter to circular spots of a foot or more across. Several common names, such as Helminthosporium leaf spot, blight, "going-out" and "dying-out," lave also been used to describe this condition.

In addition to attacking Kentucky bluegrass, the disease may also affect fescues, Ryegrass, Delta bluegrass, Canada bluegrass, Bermuda grass, Zoysia and St. Augustine grass.

"Melting-out" occurs on all parts of affected grass plants. It will be observed first in early May as small, watersoaked spots on the leaf blades. These lesions quickly enlarge to form oval, dark purplish areas on the leaf blade approximately 1/4 inch long and 1/6 to 1/8 inch wide. As these infected areas enlarge, the center of the spot becomes lighter in color, finally turning a dull white. The leaf spot stage of melting-out disease usually passes unnoticed, and does not cause serious damage.

In late May, the disease will spread to the leaf sheath, forming lesions.

Infections on the sheath are frequently so severe that the grass leaf may be girdled and killed. It is this "leaf-killing" stage of the disease that has resulted in the popular name of "melting-out." Loss of leaves may be so severe that an entire stand of bluegrass will seem to suddenly "fade" or "melt-out."

In the final stages of the disease, infection of crowns, roots and stolons occurs and infected turf will have a reddish-brown, rotten appearance that finally turns dark brown to black as secondary fungi and bacteria move in to infected areas.

’Melting-out" of bluegrass destroys lawns much faster during hot weather than during cooler periods. Sometimes it causes a sudden dying-out of large, irregular sized patches In the lawn without any visible signs of disease on the dead grass plants that appear to have died from drought.
Melting-out" is caused by two closely related fungi - -Helminthosporium vagans and sporium sativum. H. vagans does most of its damage during the cooler spring fall weather, while H. sativum is most destructive during hot summer weather.

How to Prevent "Melting-out"

A number of suggestions are offered to reduce the danger of serious damage to home lawns by melting-out" disease. There is no single recommendation that will "cure ' this dis-

PURDUE UNIVERSITY Agricultural Extension Service, Lafayette, Indiana Department of Botany and Plant Pathology, Life Science Building