(163) Organic and Biorational Fungicides for Managing Gray Mold on Raspberries

in HortScience

The increased demand for organic and sustainably grown produce has resulted in a demand for information on organic and biorational fungicides. The efficacy of these fungicides is often not established, yet they are aggressively advertised. In 2005 the efficacy of six organic and biorational fungicides and two controls were evaluated on field-grown red raspberries (Rubus idaeus `Prelude' and `Nova') for gray mold (Botrytis cinerea) management. Phytotoxicity of the fungicide treatments was evaluated on a weekly basis following each fungicide application. Fruit was harvested by hand, sorted into marketable and unmarketable categories and weighed. Subsamples of fruit were evaluated for postharvest disease development. Data analysis showed `Nova' was more susceptible to phytotoxicity than `Prelude'. The application of Phostrol resulted in the highest phytotoxicity rating when compared to all other fungicide treatments. The water spray control, standard fungicide (Captan/Elevate rotation) control, Endorse, and Lime Sulfur treatments resulted in negligible phytotoxity ratings. Applying Milstop, Milstop + Oxidate, and Oxidate + Vigor Cal Phos resulted in similar intermediate phytotoxicity ratings. Differences in marketable yield were nonexistent for the two cultivars and eight fungicide treatments. The predominant diseases observed in the postharvest evaluations were gray mold, blue mold (Penicillium sp.), and rhizopus soft rot (Rhizopus sp.) and/or mucor mold (Mucor sp.). This evaluation will be repeated in 2006.

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