Efficacy of foliar sprays of phosphates in controlling powdery mildews in field-grown nectarine, mango trees and grapevines

Foliar sprays of 0.025M and 0.04M solutions of K₂HPO₄ and KH₂PO₄ + KOH (both plus Triton X-100) and commercial systemic fungicides inhibited development of powdery mildew fungi on fruit clusters, flower clusters, fruits and leaves of field-grown grapevines, mango and nectarine. The effectiveness of phosphates in controlling powdery mildew on berries of Chardonnay grapevines was similar to that of the systemic fungicide pyrifenox (Dorado 480 EC). However, the systemic fungicides diniconazole (Marit 12.5% WP), myclobutanil (Sisthane 12E) and penconazole (Ophir), were more effective in controlling the disease on inflorescences of mango and fruits of nectarine, respectively, than either phosphate. Alternating treatments of phosphate salt with each of these fungicides, however, enhanced the inhibitory effect against the fungus in each crop. With the exception of young, newly developed nectarine leaves, these phosphate solutions were not phytotoxic to plant tissue. The inhibitory effectiveness of phosphate salts makes them useful 'biocompatible' fungicides and ideal foliar fertilizers for field application for disease control.