Annual vinca (Catharanthus roseus) were grown in containers in a greenhouse and irrigated with a complete nutrient solution containing phosphite (0, 0.1, 0.3 mM), phosphate (0, 0.3, 0.5 mM), or combinations of these two compounds as a source of phosphorus. After 2 weeks, the plants were sprayed with a Phytophthora nicotianae zoospore inoculum to evaluate the potential for phosphite to protect annual vinca from Phytophthora shoot blight. To determine the extent and duration of protection from shoot blight provided by phosphite foliar applications, the plants were treated with phosphite foliar sprays (0.5 mM) at various intervals, and then inoculated. Application of phosphite to the soil/roots provided no protection from Phytophthora shoot blight. However, foliar applications of phosphite at a concentration of 0.5 mM at three to six day intervals gave protection similar to foliar applications of Aliette fungicide at 3 g/liter (2.5 lb/100 gal) applied at 14 day intervals.

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Author notes

This research was funded in part by a grant from the USDA/Southern Region IPM Program.

2Associate Professor, Dept. of Horticulture.

3Assistant Professor, Dept. of Plant Pathology, Physiology, and Weed Science.