Biorational Fungicides to Manage Cucurbit Powdery Mildew on Winter Squash in New York

Abstract

Cucurbit powdery mildew (CPM) is one of the most common foliar diseases of winter squash grown in New York. Conventional fungicides remain the primary method for managing CPM. However, increasing consumer demand for organic produce and concerns about both environmental safety and fungicide resistance development have driven research to identify alternative management strategies. Biorational fungicides, including biologicals, botanicals, and minerals, are increasingly available for certified organic production but are generally considered less effective at managing CPM than conventional products. Copper-containing pesticides approved for use in organic production are effective, but concerns about nontarget effects are driving exploration of alternative biorational solutions for CPM. Further research is warranted to validate and expand management strategies for organic cucurbit production. In this study, we evaluated 9 and 10 biorational fungicides to reduce CPM on winter squash in field trials in 2021 and 2022, respectively. The treatment that consistently and most effectively reduced disease severity was Kocide 3000-O (copper hydroxide) followed by Theia ( Bacillus subtilis) and Regalia plus Stargus ( Reynoutria sachalinensis plus B. amyloliquefaciens). The developmental product Curezin (copper zinc) and the adjuvant Dyne-Amic (alkylphenol ethoxylate) also significantly reduced disease compared with the untreated control in 2022. No differences in yield were observed in either year. We conclude that copper-based biorational fungicides most effectively managed CPM compared with other biological and botanical products evaluated, followed by Theia and Regalia plus Stargus. Knowledge gained from this study can inform current CPM management practices and the development of future tools for IPM strategies.