Evaluating Fungicides in Production for Long-term Management of Impatiens Downy Mildew in the Landscape

Abstract

Since the emergence of impatiens downy mildew (Plasmopara obducens J. Schröt), economic losses to Florida’s $16 billion landscape industry are estimated to exceed $50 million annually. Researchers have come to the conclusion that chemical control is the only effective short-term management option available. The greatest challenge is cost effective management of impatiens downy mildew in the landscape. Some of our first trials conducted early in Spring 2012 revealed that impatiens transplanted into landscape beds incorporated with a granular form of mefenoxam remained healthy for 60 days. Subsequent experiments evaluating products for long residual (> 30 days) control have identified several additional chemistries including fluopicolide, various phosphonates and oxathiapiprolin as promising. Further studies investigated the potential for eradicative control and found phosphonate containing products effective even after infection. Most recent studies have focused on fungicide rotations targeting long term residual control of impa-tiens downy mildew. Weekly preventative fungicide spray rotations on potted impatiens in production have included cyazofamid, dimethomorph, fluopicolide, mefenoxam, potassium phosphite, and oxathiapiprolin. To date, oxathiapip-rolin has provided stellar control of impatiens downy mildew when used alone and in every rotation study. Results obtained from fungicide efficacy trials conducted over the past four years indicate that some chemistries provide long enough residual control for impatiens to remain untreated in the landscape. These disease management studies will directly impact commercial producers and landscape professionals alike, as homeowners will benefit from not having to apply pesticides.