Foliar applications of mono-potassium phosphate fertilizer inhibit powdery mildew development in nectarine trees

Abstract

Foliar applications of 1% solution of mono-potassium phosphae (MKP = KH2P04) fertilizer plus Triton X-100 (0.025%), sterol inhibiting (SI) fungicides, and an alternating treatment of phosphate fertilizer and SI fungicides inhibited development of the powdery mildew fungus Sphaerotheca pannosa on fruits and leaves of nectarine trees in 3 consecutive years. The effectiveness of the alternating treatments with an appropriate systemic fungicide and 1% solution of MKP was similar to that of the commercial treatment with the systemic fungicides alone. However, application of the systemic fungicides only, omitting the phosphate treatment when they were scheduled, was significantly less effective than either the phosphate or the alternation treatments. These results indicate that the use of phosphate fertilizer has a significant role in disease control, enabling up to 50% reduction with number of fungicide treatments required for powdery mildew control. These results were confirmed in a large-scale demonstration trial conducted in a commercial orchard in 1995. This trial also revealed that a tank-mix treatment of 1% MKP solution with an SI fungicide provided the best protection against powdery mildew. Phosphate solutions were not phytotoxic to plants. Fruit harvested from MKP-treated trees by either alternation or tank-mix were similar or larger in their size distribution to those harvested from the commercial fungicide-based treatment. Fruit harvested from control, nontreated, trees were much smaller and produced ca. 23% nonmarketable fruits. The inhibitory effectiveness of MKP against powdery mildew in nectarine makes it a potential major component of an integrated pest management program.