Golf Course Management

FEB 2018

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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82 GOLF COURSE MANAGEMENT 02.18 duced fungicide rates or fewer threshold-based applications of fungicides (extending the in - terval between sprays) when BMPs (greater nitrogen and higher mowing) were used. Fun - gicide efficacy was always best under greater nitrogen fertility, where the fungicide rate could be lowered to 25% of label rates (a 75% reduction) and still provide acceptable disease control. This study also found that threshold- based fungicide management of anthracnose was feasible; the number of fungicide applica - tions to control anthracnose was reduced by 80% when mowing height was higher (0.125 inch) and turf was fertilized with more nitro - gen (4 pounds/1,000 square feet/year). Preventive fungicide applications have typically been considered more effective than curative applications for the control of anthracnose (1,23), and mixtures of two or more active ingredients applied as a tank-mix or prepackaged product often perform better than individual products for the control of an - thracnose on annual bluegrass putting green turf (32). Moreover, combinations of different fungicide chemistries can broaden the num - ber of diseases controlled, as well as reduce the potential for the development of fungicide re - sistance. Preventive applications are often recom - mended at least three to four weeks before the typical onset of the disease symptoms on sites with a previous history of anthracnose. The purpose of preventive applications is to reduce the population of Colletotri um cereale in the sward before environmental conditions con - ducive to anthracnose (hot, humid weather) occur. However, as stated above, early cura - tive (threshold) sprays can result in significant reductions in fungicide inputs and excellent disease control as long as BMPs are followed. Other research has shown that fungicides should be applied in 2 gallons of water/1,000 square feet (81.49 milliliters/square meter), using nozzles that produce a medium-to- coarse droplet size to optimize control (5,23). Currently, 12 fungicide groups (chemi - cal classes) are labeled for the control of an- thracnose on cool-season turf (Table 1). Of these groups, the demethylation inhibitors (DMI); quinone outside inhibitors (QoI or strobilurins), benzimidazoles, polyoxins and nitriles have been the most efficacious against anthracnose. Other chemical classes including the phosphonate, dicarboximide, phenylpyr - role and SDHI fungicides have been most ef- fective when applied in a mixture with other anthracnose fungicides. Whatever fungicides are used, it is good practice to avoid the con - tinuous use of any product to reduce the po- tential for fungicide resistance. For a list of current anthracnose fungicides and combina - tion products and their efficacy against this disease, refer to Tables 1 and 2, respectively. Fungicide resistance management For anthracnose, resistance has been re- ported for the benzimidazole and QoI fungi- cide groups, and reduced sensitivity (reduced interval and/or rate response) has been identi - fied with the DMI fungicides (1,34). The Fun- gicide Resistance Action Committee (FRAC; www.frac.info/) has developed strategies to reduce the risk of resistance to fungicides. • Use BMPs to reduce disease pressure. • Limit the total number of fungicide appli - cations (for example, no more than three to four SDHI applications/year) for chemical classes that have a high potential for resis - tance (see Tables 1 and 2). • Alternate fungicides with different modes of action (avoid sequential applications ex - cept for contact fungicides). • Tank-mix fungicides that have different modes of action, and be sure that all of the components of a mixture are active against the target pathogen. • Rely on preventive applications for diseases that have previously been severe on the site and have a high risk of resistance (for exam - ple, anthracnose, dollar spot, gray leaf spot, Microdochium patch and Pythium blight). • Avoid late-curative and reduced-rate appli - cations that can put pressure on the patho- gen to develop resistant strains, particularly for high-risk fungicide groups (for example, DMI, benzimidazole, QoI and dicarboxi - mide fungicides). Sand topdressing had a greater impact on reducing disease and improving playability under conditions of lower mowing and lower nitrogen fertilization. HOC, height of cut. Photo by James Hempfling

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