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- Author or Editor: Robert A. Van Steenwyk x
Walnut husk fly (Rhagoletis completa) is a major pest of English walnuts in California. Research was initiated in 1995 to evaluate reduced-risk pesticides. The first effective control measures were found in 2001—spinosad plus bait and kaolin (Surround). Spinosad was registered for organic use in 2003 as GF-120 NF (a formulation of spinosad and bait) and Entrust (a spinosad formulation to be mixed with existing baits). GF-120 is recommended for low to moderate populations while Entrust + bait is recommended for higher populations. Entrust + bait is price competitive with the standard malathion + bait. Kaolin is also effective for walnut husk fly control; however, control is dependent upon adequate coverage. In 2004, varietal susceptibility was assessed. The cultivars `Payne', `Serr', `Pedro', and `Hartley' were found to be highly susceptible while `Chandler' and `Howard' were somewhat resistant. Infestation in `Chandler' began later in the season than in other cultivars. Quality parameters were also measured. Samples of 100 infested and uninfested `Tulare' walnuts were compared at harvest. There were significant differences in adhering hull, percentage of edible yield, and relative value between infested and uninfested nuts. The relative value of infested nuts was 28% less than uninfested nuts. There were minimal differences in percentage of mold and kernel color. Walnuts sprayed with kaolin had larger nuts, fewer external defects, and an earlier harvest timing.