Local and systemic control of powdery mildew (Leveillula taurica) on pepper plants by foliar spray of mono-potassium phosphate

A foliar spray of 1% (w/v) solution of the fertilizer mono-potassium phosphate (MKP) (KH₂PO₄) on the upper surfaces of lower leaves of greenhouse-grown peppers induced local and systemic control against Leveillula taurica, as compared with control plants. This protection was expressed by a reduction in the leaf area covered with sporulating colonies and in conidial production on leaf tissue, 24 or 48 h post-treatment, when MKP was applied on lower leaves of plants that had been exposed to the source of inoculum. Foliar application of MKP, initiated before or after exposure to heavily diseased plants as the source of inoculum, was effective in controlling powdery mildew. Application of MKP efficiently suppressed powdery mildew as expressed by inhibition of the development of new sporulating colonies, as well as the conidial production of the fungus on infected tissue. Microscopic examination indicated destruction of both hyphae and conidial structures on MKP-treated leaves. The efficacy of MKP in controlling powdery mildew on greenhouse-grown plants was compared with a sterol-inhibiting systemic fungicide. Both treatments significantly inhibited powdery mildew as compared with non-treated control plants, although the fungicide-based treatment seemed to be slightly more effective (not significant) in controlling the disease. Phosphate solutions were not phytotoxic to plant tissue and did not affect the yield, as compared with the fungicide treatment. However, a lower yield was recorded for the non-treated control plots because of mildew infection on leaves. These data indicate that MKP spray may be applied as an alternative practice for the control of powdery mildew in peppers.