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Poster: Biology & Disease Mgmt: Chemical Control


Yield loss and management of orange cane blotch of blackberry, caused by the alga Cephaleuros virescens
F. BROWNE (1), P. Brannen (1), H. Scherm (1), L. Fall (1), J. Taylor (2), J. Shealey (3), E. Beasley (1) (1) University of Georgia, U.S.A.; (2) University of Georgia, U.S.A.; (3) University of Georgia, U.S.A.

The alga Cephaleuros virescens causes orange cane blotch (OCB), a serious disease of blackberries in the southeastern United States. OCB impact on blackberry growth and yield was assessed. Neither cane diameter nor fruit size were significantly impacted by severity of OCB; however, maximum fruit number per cane decreased by 80% with increasing OCB severity, thereby resulting in reduced yields. Field efficacy trials with diverse algicides, disinfectants, and fungicides were conducted over a 3-year period from 2013 to 2015 at two locations on a thornless blackberry cultivar, ‘Ouachita’. Treatments, applied during the summer and fall, included ametoctradin + dimethomorph, calcium polysulfide, calcium polysulfide + surfactants, captan, chlorothalonil, copper hydroxide, copper hydroxide + hydrogen dioxide, fluazinam, fluopicolide, hydrogen dioxide, mancozeb, mancozeb + copper hydroxide, mandipropamid, mefenoxam, mefenoxam + copper hydroxide, mefenoxam + mancozeb, potassium phosphite, potassium phosphite + captan, potassium phosphite + copper hydroxide, oxathiapiprolin and diluted sodium hypochlorite. Potassium phosphite, generally active on both oomycetes and fungi, was the only chemical that provided significant suppression of the disease, with 48-80% reduced lesion coverage of canes. Management of OCB will be difficult in light of the limited number of labeled applications of potassium phosphite allowed and the potentially long infection period of the pathogen.