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Abstract
Orange cane blotch (OCB), caused by the alga Cephaleuros virescens, is prevalent in commercial blackberry plantings in the southeastern United States. The pathogen produces prominent blotches on the surface of canes; affected plant tissue may crack over time, compromising the cane surface. Light and electron microscopy were used to characterize cane damage caused by C. virescens in more detail. Algal filaments were observed growing intercellularly and occasionally intracellularly underneath the cuticle and among epidermal layers of host tissue. Field studies at four commercial sites were conducted over 2 years to assess the yield impact of OCB. Fruit numbers per cane decreased with increasing disease intensity, but neither cane diameter nor fruit size were affected. In 3-year field efficacy trials to identify suitable agrichemicals for control of OCB, potassium phosphite was the only product that consistently and significantly suppressed the disease when applied during summer and fall.