A new, potentially serious pest of sweet cherries showed up recently in ripening cherries in Northern California orchards. It has been tentatively identified as a drosophilid fruit fly of unknown genus and species, says Bill Coates, a University of California Cooperative Extension farm advisor for San Benito, Santa Cruz, Santa Clara and Monterey Counties.
These are flies usually associated with damaged or decaying fruit and are called vinegar flies, says Coates. In this particular case the fruit appears undamaged except for what appears to be ‘stings’ on the surface of the fruit and maggots feeding within the fruit. Early varieties such as Early Burlat and Black Tartarian have been extensively damaged in Santa Clara County. Growers are beginning to apply protective sprays to guard against infestation of the main ‘Bing’ crop.
The pest has also appeared in the northern San Joaquin Valley, says Coates, who adds that he doesn’t yet know whether other fruits are susceptible. This is an excellent example of the collaboration between growers, pest control advisers, UC Cooperative Extension, agricultural commissioners and the California Department of Food and Agriculture, he says.
“I was first informed of this pest on Thursday, May 14 by a pest control adviser and a cherry grower,” he says. “I was able to determine from the symptoms that it was not light brown apple moth but a fruit fly of some type. I provided fruit fly traps to growers by late Thursday. On Friday samples from both infested fruit and fruit fly traps were taken by the Santa Clara County Agricultural Commissioners office to Sacramento for identification by the CDFA.”
The species of drosophila has still not been confirmed by the CDFA, says Coates. It does not seem to match existing North American species. These are drosophilid, not tephritid fruit flies – the latter group contains most of our common fruit-infesting fruit flies. It has been found infesting cherries in Santa Clara, Yolo and Stanislaus counties with unconfirmed reports from other counties. A similar, if not the same drosophila, is also infesting strawberries and caneberries in Santa Cruz County.
“Most cherry growers in the Central Coast are applying multiple GF-120 bait sprays and doing extensive sorting of fruit. I am trying a variety of trap types but the presence of the common drosophila species – drosophila melanogaster, complicates monitoring,” says Coates. “Currently, the best indication of infestation is to check early-ripening pollenizers such as Black Tartarian and Early Burlat and then apply controls to protect the main Bing crop. There is no replicated research on control measures for these type of flies in California in cherry orchards.”