P-093 - Polyoxin D Zinc Salt (OSO 5%SC) Offers Organic Vegetable Growers Improved Disease Control

Organic vegetable producers have struggled to achieve acceptable disease control levels utilizing OMRI-approved fungicides.  Traditionally, fixed copper and sulfur compounds have been the backbone of these production systems.  These spray programs have often failed to produce acceptable disease control levels and growers are consistently looking for suitable program additions to lower disease pressure.  Over 2002-2004 we conducted a total of seven research trials at Virginia Tech’s Homefield Farm in Blacksburg, VA focusing on the efficacy of polyoxin D zinc salt (OSO 5%SC; Certis USA LLC, Columbia, MD) on cucurbit powdery mildew (Podosphaera xanthii; two trials), tomato early blight (Alternaria solani; two trials), and Alternia blight and head rot of broccoli (Alternaria sp.; three trials).  For all seven trials, polyoxin D significantly reduced disease severity (p < 0.05) when compared to the nontreated control and significantly increased yields in four of the seven trials.  In the cucurbit trials, polyoxin D offered statistically similar control levels when compared to plots receiving applications of the commercial standard sulfur (Yellow Jacket Wettable Sulfur II; Georgia Gulf Sulfur Corporation, Valdosta, GA).  In both tomato trials, disease severity was further suppressed when polyoxin D and copper octanoate (Cueva Fungicide Concentrate; Certis USA LLC, Columbia MD) were tank-mixed and applied compared to when materials were used solely.  results indicate that polyoxin D is a useful material for organic disease control of various fungal disease in vegetables.