Superintendents in cool-season turfgrass zones once looked to late August as the peak of their season. With the worst heat dissipating, they looked to lower temperatures to allow weary grasses, and workers, to recuperate.

Last year, that could not have been further from the truth. During much of August and September, the perennial ryegrasses on courses from the Atlantic coast to Nebraska withered as if they had been sprayed with herbicide by a vandal. The cause was not a prankster but Pyricularia grisea, a new invader called gray leaf spot. Until recently only a research footnote, it has progressed into an epidemic.

Just eight years ago a pair of Penn State researchers, Dr. Peter Landschoot and Bryce Hoyland, found gray leaf spot on two courses in their state. The disease received scant attention over the next three years because it only caused foliar, or leaf, damage and left mature plants unaffected.

Then in 1995, the disease caused devastating losses of up to 90 percent on fairways and rough. By last summer, gray leaf spot had spread into nearly 20 states, and now it is considered a threat for wider infestation.

Prior to breeding efforts in the 1960s, perennial ryegrass was a difficult turf to mow — the end of the leaf would tear instead of cut cleanly — and was not used on many courses. After its improvement through selective breeding, many courses used it as a permanent monostand.

Gray leaf spot, conversely, was all but invisible. The relative unimportance of the disease early on meant scientists spent little time studying its management and control. As a result, there are far more questions today than answers.

An outbreak becomes apparent with reddish-brown spots on leaf blades, in turf patches about six to eight inches in diameter. Although the symptoms of gray leaf spot can be confused with other diseases, immediate confirmation of potential infections by a turfgrass pathologist is important, since entire fairways can become infected within days.

Early symptoms are even less obvious on seedling perennial ryegrass since leaf blades are slender and lesions are invisible to the naked eye. A distinct twisting of the leaf tip, which causes blades to look like small fishhooks, is the easiest way to identify outbreaks.

The good news is that fungicide combinations have proved successful in controlling the disease. The bad news is that anywhere from three to 15 applications are required since disease activity cannot be predicted. In addition, the disease can remain virulent until recurring hard frosts. For courses with tight budgets that have not had to treat perennial ryegrass, fungicide costs of $20,000 to $50,000 (depending on acreage and conditions) have increased the price of keeping turf alive.

This new invader has shown to be a formidable opponent and has, in many respects, humbled the turfgrass industry. The USGA Green Section will keep in touch with researchers and act as a clearinghouse of information for courses that may be struck by the disease. Golfers should be aware that gray leaf spot presents new challenges to the turfgrass industry and that taking bold management steps will be necessary to prevent future outbreaks.