Reuveni, M., Golan Research Institute, University of Haifa, P.O. Box 97, Qasrine 12900, Israel
Harpaz, M., Extension Service, Ministry of Agriculture, Zefat 13100, Israel
Reuveni, R., Dept. of Plant Pathology, ARO, Newe Ya'ar Research Center, P.O. Box 1021, Ramat Yishay 30095, Israel

Foliar sprays of solutions of di-potassium hydrogen orthophosphate, K2HPO4 (DKP) and potassium di-hydrogen orthophosphate, KH2PO4 (MKP), commercial systemic fungicides, and an alternating treatment with phosphate fertilizer and systemic fungicides inhibited development of the powdery mildew fungus, Oidium mangiferae, on flowers and bloom clusters of field-grown mango trees. The effectiveness of the alternation treatments with an appropriate systemic fungicide and 1% solution of mono-potassium phosphate (MKP) in controlling powdery mildew on bloom clusters was similar to that of the commercial treatment with the systemic fungicides. However, application of the systemic fungicides alone, on the same dates on which they were applied in the alternation treatment, without application of the phosphate treatment was significantly less effective in controlling the disease than either the phosphate or the alternation treatment. This indicates that the use of phosphate fertilizer has a significant role in disease control and that it can reduce the number of fungicide treatments necessary against powdery mildew by up to 50%. These results were confirmed in large-scale demonstration thais conducted in commercial orchards in 1994 and 1995. Our 1997 findings also revealed that tank-mix treatments of 1 % MKP solution with half the recommended quantity of sterol inhibitor fungicide applied at 14-day intervals provided a protection against powdery mildew comparable with or superior to that given by the standard fungicides-based treatment applied at 7-day intervals. Tank-mix treatments of MKP (1%) with sterol inhibitor at the recommended rate or with the new strobilurin Kresoxym-methyl (BAS 490F, strobi), or the BAS 490F alone, were the most effective, and provided >95% protection against O. mangiferae, compared with the control. Phosphate solutions were found not to be phytotoxic to plant tissue. These treatments affected the yield of mango trees: a significantly lower yield was observed on control untreated trees, probably because of powdery mildew infection on flowers. The inhibitory effectiveness of phosphate salts makes them a potential major component of an integrated pest management program.