DISEASES

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Aerial Blight (Phytophthora parasitica) Most susceptible plants: vinca. This fungal pathogen causes a major disease in vinca in the landscape but it can also be a serious disease of greenhouse-grown vinca. Symptoms: Initial symptoms of infection occur on leaves. Leaf infection is characterized by a rapid collapse of the leaf. Infection progresses to the leaf petiole and to the location of the attachment of the petiole to the plant stem. A brown, sunken stem lesion develops at the point where the petiole attaches to the stem. This brown stem lesion develops on the stem causing stem collapse. If wet conditions persist following plant infection, the fungus will grow to the base of the plant resulting in plant death. A unique feature of Phytophthora aerial blight is its decided aerial nature; this fungus rarely causes a primary root rot but causes massive damage to the aerial portion of the plant. Control: Control of this disease has been very difficult and has proven impossible in many situations. Most effective control in the greenhouse will require that the plants are grown on benches, as far above soil as feasible. Remove symptomatic plants as soon as they become obvious on the greenhouse bench. Although foliar-fungicides have not been totally satisfactory, and have failed totally in the landscape for control of this disease, application may be useful in greenhouse situations if applied at the first sign of disease.