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Dormant treatments with chlorothalonil-oil delay the production of primary inoculum of almond scab caused by Fusicladium carpophilum
J. Adaskaveg (1), H. FORSTER (1). (1) University of California, Riverside, CA, U.S.A.

Almond scab has gained increased importance in California almond production due to QoI and SDHI resistance in populations of the pathogen <i>Fusicladium carpophilum</i>. The pathogen overwinters in lesions on <1 year-old twigs. These lesions provide primary inoculum in the spring when the fungus produces abundant wind- and rain-borne conidia that infect young leaves that may lead to premature tree defoliation. Chemical management strategies for scab currently include dormant copper-oil applications that delay the sporulation of twig lesions, and protective in-season treatments that prevent new infections in the spring. Field trials were conducted to evaluate the efficacy of alternative dormant treatments on the production of primary inoculum. Chlorothalonil and other fungicides were compared to copper, all in mixture with an agricultural oil. A single treatment was applied in mid- to late-January and sporulation of twig lesions was evaluated periodically between March and May. Chlorothalonil-oil delayed and reduced the amount of sporulation of twig lesions until late May and was significantly more effective than the other treatments. The delay of sporulation allows a more effective use of subsequent in-season protective treatments and aligns the application of in-season treatments for scab with those for other summer diseases such as Alternaria leaf spot, rust, and hull rot and thus, reduces the total amount of fungicide applications per season.

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