Control of the foliar disease, Septoria lycopersici, in organic tomato producton

Abstract

<p>Disease management in organic tomato (Lycopersci esculentum Mill.) production in humid climates poses challenges for producers. Septoria leaf spot (Septoria lycopersici Speg.) is a common disease of tomatoes in areas with high humidity and varying temperatures from 20 to 25 0C. New commercial products and techniques are becoming available to control S. lycopersici, but their efficacy has not been adequately tested. Our objective was to evaluate the efficacy of organic fungicides and compost teas. The teas were made from either windrow-composted cattle manure (WCCM) or vermicomposted cattle manure (VCCM). We also compared the efficacy of organic and conventional fungicides. Tomato plants ('Mountain Spring") were inoculated with 7.5 x 108 conidia·ha−1 and treated with: (i) control (no foliar spray), (ii) alternated applications of chlorothalonil plus copper hydroxide and mancozeb plus copper hydroxide (iii) copper hydroxide only, (iv) Bacillus subtilis only, (v) WCCM tea, and (vi) VCCM tea. Copper hydroxide reduced disease severity caused by S. lycopersici and the addition of chlorothalonil or mancozeb did not increase yield or decrease disease severity. Neither compost tea, Serenade, nor Sporan reduced disease severity caused by the bacterial speck/bacterial spot complex and S. lycopersici. Because many factors can influence compost tea efficacy a growth chamber experiment was carried out to evaluate the efficacy of compost tea from either WCCM or VCCM with or without nutrient additives to control S. lycopersici on tomatoes. The efficacy of compost tea made from a SoilSoup brewer was also tested. Tomato plants ('Mountain Spring") were started in a greenhouse and then moved into three growth chambers (replications), inoculated with 1000 conidia/mL and treated with: (i) control (no foliar spray), (ii) WCCM, (iii) WCCM tea plus a nutrient solution, (iv) VCCM tea, (v) VCCM tea plus a nutrient solution, and (VI) SoilSoup compost tea. The experiment was repeated once. The addition of fermentation nutrients did not increase compost tea efficacy. The use of commercial brewing equipment did not increase compost tea efficacy. Compost source did not affect tea efficacy. Further research is necessary to determine the role compost teas have on controlling S. lycopersici in organic tomato production.</p>