Golfdom, October 2011

FIGURE 1 FIGURE 2 30 TurfGrass Trends October 2011 www turfgrasstrends com d o l l a r s p o t Dollar spot can infect both warm and cool season turfgrass species Primary species affected are Kentucky bluegrass bentgrass tall fescues zoysiagrass bermudagrass and seashore paspalum Disease severity is most commonly seen in the spring and fall on warmand cool season species while warm season species can remain susceptible throughout the summer months On fine textured and closely mown turf such as golf course putting greens and fairways the disease symptoms are characterized by round straw colored sunken patches ranging from the size of a U S quarter to the size of a U S silver dollar about 1 to 2 inches in diameter Figure 1 If the disease becomes severe individual patches may coalesce forming larger irregular patches of blighted turfgrass that can die back to the soil surface On residential lawns where turf is maintained at higher mowing heights the dead spots appear larger and more diffuse 2 to 3 inches in diameter Under those conditions dollar spot can be distinguished by characteristic lesions that are light tan with a reddish brown border usually radiating from the margins of the leaf blades Leaf lesions can expand extending across the entire leaf resulting in girdling of blades and dieback from leaf tips Individual leaf blades may have a single lesion many small lesions or be entirely blighted A more certain diagnosis of the disease can be made by examining the grayish white fluffy mycelium in the early morning before the turf has been mowed The mycelium of the fungus can usually be seen spreading outward from the infected lesions to adjacent host tissues Figure 2 To meet the high expectation of aesthetic quality and playability golf course superintendents and athletic field managers have relied on fungicide applications cultural practices and the use of nitrogen fertilizers to obtain acceptable control Fungicides must be applied at labeled rates when environmental conditions are favorable for disease development To limit the possibility of fungicide resistance it is important to alternate the use of fungicides that have different modes of action The Fungicide Resistance Action Committee FRAC coding is a tool turfgrass managers can use to know which fungicides have similar modes of action FRAC gives fungicides a certain number or letter code e g 4 M2 or U based on their chemistry The practical application of FRAC is it gives turfgrass managers an easy method for determining which fungicides to alternate For example Banner Maxx and Eagle have a FRAC code of 3 They both inhibit cell membrane synthesis Therefore the possibility of resistance would be greater if they were only alternated with each other in a season long disease control program Accordingly the development of resistance to dollar spot would be less likely if fungicides like Heritage 11 and Daconil Ultrex M4 were alternated during a grow PHOTOS COURTESY J B WORkman Continued from page 29 Dollar spot on greens and fairways Figure 1 can range in size from a quarter to a silver dollar A certain diagnosis of dollar spot can be made by examining the grayish white fluffy mycelium Figure 2 in the early morning hours before the turf has been mowed