We have just documented the first case of gray leaf spot this year from a golf course in Bloomington . We have learned that the disease will develop over a broad range of environmental conditions (not just hot and wet) and it continues to be very dry south of Indianapolis . Our research results showed that the presence of inoculum is the disease-limiting factor north of the Ohio River . After all, the pathogen population does not regularly survive midwestern winters, unless they are very mild (not last winter). Outbreaks can be expected in southern Indiana , but the threat to perennial ryegrass in the northern third of the state is limited. In between, disease occurrence will be sporadic. Those stands of perennial ryegrass that had significant gray leaf spot problems in 2005 or 2006 should be watched most closely, because it is quite likely that the pathogen population survived the winter in numbers sufficient to threaten turf this summer. Once the disease is identified in a given area, other perennial ryegrass stands (mostly juvenile rye) are at risk. Newly seeded ryegrass will be under the greatest threat. Several fungicides may be effective in suppressing disease development including the strobilurin products (Heritage, Disarm, Compass, Insignia) and thiophanate methyl (Cleary’s 3336 and others). Chlorothalonil and the DMI fungicides a somewhat less effective.
Extensive information on gray leaf spot can be found at http://www.extension.purdue.edu/extmedia/BP/BP-107-W.pdf . If you suspect an outbreak of gray leaf spot has occurred on your course, and wish to discuss management options, please contact Rick Latin at rlatin@purdue.edu or 765-494-4639.