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Management of bitter rot of apple under optimal conditions for disease development in Georgia orchards

Phillip Brannen: University of Georgia

<div>Bitter rot of apple, caused by members of the <em>Colletotrichum</em> <em>acutatum</em> and <em>C</em>. <em>gloeosporioides </em>species complex, is a major disease of apples in the southeastern U.S., and hot, humid/wet conditions in Georgia are generally conducive to disease development. As warmer conditions prevail, bitter rot has actually increased in importance, and management has become more difficult. New fungicides have been recently registered for management of bitter rot, but recommendations for utilization in spray programs were lacking. Over multiple years, Captan + ProPhyt (potassium phosphite) applications have provided significant management of bitter rot (n=3; 89.3% control), and this combination was utilized as the chemical standard for comparison of new fungicides and combinations of fungicides in multiple years of testing. Pristine (pyraclostrobin + boscalid), Merivon (fluxapyroxad + pyraclostrobin) and Luna Sensation (fluopyram + trifloxystrobin) consistently provided equivalent control to that of the standard, but Pristine + ProPhyt was not better than the standard in any trial. Under severe disease conditions, a three-way combination of Captan + ProPhyt combined with Manzate Prostick (mancozeb) provided better control than Captan + ProPhyt alone. Three-way combinations with Captan + ProPhyt combined with Merivon, Inspire Super (difenoconazole + cyprodinil), or Omega 500F (fluazinam) were not as consistent in their benefit over the standard.</div>