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ISHS Acta Horticulturae 1133: XI International Rubus and Ribes Symposium

Assessment of algicides, disinfectants and fungicides for control of orange cane blotch caused by the alga Cephaleuros virescens

Authors:   F.B. Browne, L.A. Fall, P.M. Brannen, J. Taylor, J. Shealey, E.D. Beasley
Keywords:   Cephaleuros virescens, algae, blackberry, Rubus fruticosus, fungicide, algicide, disinfectant, orange cane blotch, orange felt, potassium phosphite
DOI:   10.17660/ActaHortic.2016.1133.77
Numerous algicides, disinfectants and fungicides were tested for efficacy against orange cane blotch, caused by the alga Cephaleuros virescens. Orange cane blotch is observed in climates that are wet, humid, and hot. The alga initially forms yellow, disk-shaped spots on canes; spots eventually develop into orange blotches, and colonies coalesce to cover large areas of cane surfaces. The objective of this research was to develop efficient ways to control this parasitic alga. Efficacy trials were conducted over a period of two years and two locations on a thornless blackberry cultivar, 'Ouachita'. Treatments assessed in year one included calcium polysulfide, calcium polysulfide + surfactants, chlorothalonil, copper hydroxide, fluazinam, hydrogen dioxide, mancozeb, mancozeb + copper hydroxide, potassium benzoate, potassium phosphite, potassium sorbate, and diluted sodium hypochlorite. Potassium phosphite, generally active on both oomycetes and fungi, was the only chemical that provided significant suppression of the disease in the first year of testing. Since oomycetes and algae are more closely related than fungi, the list of chemicals tested in the second year was targeted to include additional oomycete-active materials: ametoctradin + dimethomorph, captan, copper hydroxide, fluopicolide, mancozeb, mandipropamid, mefenoxam, mefenoxam + copper hydroxide, mefenoxam + mancozeb, potassium phosphite, potassium phosphite + captan, potassium phosphite + copper hydroxide, and oxathiapiprolin. Potassium phosphite again provided disease suppression in the second year of testing; indeed, potassium phosphite was the only product that provided consistent disease control among the eighteen products tested, indicating that control of orange cane blotch 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.

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