Fruit and Vegetable Magazine - November/December 2009


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A tiny vinegar fly, known as the spotted wing drosophila (Drosophila suzukii), is causing damage in strawberries, blueberries, blackberries, raspberries, and cherries throughout California, and was most recently reported in an Oregon vineyard. There are also reports the pest can infest plums and peaches. How much trouble can this little critter cause? According to Oregon State University entomologist Amy Dreves, spotted wing drosophila (SWD) was first reported in North America in 2008 in California and Florida. During the 2009 season, the pest caused damage to one-third of California’s cherry crop, hit some Oregon peach orchards so bad there were reports of 80 per cent crop losses, and snacked on Oregon raspberries to the tune of 20 per cent crop losses. As of August 2009, spotted wing drosophila has been reported throughout California, in 12 Oregon counties and from Vancouver, Wash., to Abbottsford, B.C. In Oregon alone, there are weekly reports of its spread to new locations within the state. Agricultural extension workers in the western U.S. gathered at the University of California this past August for an “emergency” meeting to discuss the pest and develop a plan of attack. There is deep concern within the U.S. horticultural community that the pest could devastate California’s wine industry. Spotted wing drosophila is native to South East Asia, including India, Bangladesh, and South east China. It can also be found in Japan, Korea and Hawaii. While the female of the species looks like a regular vinegar or fruit fly, the males can be identified through the small black spots visible on their wings. According to researchers, if you have male SWD in your orchard or patch, it’s assured the female flies present are also SWD. While most vinegar or fruit flies lay their eggs on the surface of objects, SWD females possess ovipositors designed to cut through the surface of fruit like a small saw. Once the surface is breached, the female deposits one of two eggs per fruit at a depth of about one or two millimetres. She has the capacity to lay about 300 eggs in all. Heat is required for the SWD eggs to hatch. The colder it is, the longer it takes. At 82 degrees Fahrenheit, a new generation can develop every seven days. In California, it’s expected that SWD can produce 10 generations a year. Fruit attacked by the SWD reveal only a soft spot on the surface with no hole visible. When the soft spot is cut into, the larvae, which undergo three instars before pupating, may be visible. Only the larvae are destructive to the fruit. According to Mark Bolda, a strawberry and caneberry farm advisor with UCDavis, the U.S. Department of Agriculture (USDA) and the California Department of Food and Agriculture (CDFA) are not recommending any regulatory action or quarantines for SWD at the moment. Bolda recommends that growers monitor for the pest by using traps. The best attractant he has found is made by mixing one packet of baker’s yeast with four teaspoons of sugar in about 12 fluid ounces of water. The mixture can then be distributed between five or six containers and then placed in the orchard or patch as a sentinel trap. The U.S. researchers have also conducted spray tests, finding that Entrust provided short-term efficacy while malathion produced excellent control, even after 14 days. According to Bolda, the collaborating grower also tried a spray of Diazinon 50W on raspberries that had finished harvest, resulting in a high number of flies being killed. “There are several important topics to discuss concerning the results of these chemical efficacy trials,” he stated in his growers’ blog. Also key for controlling SWD is proper field sanitation. Since the insect likes to feed on rotten fruit and needs fruit in order to reproduce, it’s important to remove overripe and rotten fruit from the orchard or patch, says Bolda. He advises that strawberry producers follow the same sanitation strategies as those used to control Botrytis grey mold or Rhizopus rot – remove rotten or overripe fruit from under the canopy and place it in the row so it can be mashed by passing farm machinery or feet. For raspberries, it’s more difficult. Bolda advises that caneberry growers remove all cull fruit from the field and destroy it elsewhere. For more information on spotted wing drosophila and to see photos of the pest, check out these websites: caneberries home Keeping it fresh A Georgia State University professor has developed an innovative way to keep produce fresh for long periods of time. Microbiologist George Pierce’s method uses a naturally occurring microorganism – no larger than the width of a human hair – to induce enzymes that extend the ripening time of fruits and vegetables. The process does not involve genetic engineering or pathogens, but involves micro-organisms known to be associated with plants and considered to be helpful and beneficial to them. The process works by manipulating the organism’s diet so that it will over express certain enzymes and activities that work in the ripening process. Pierce analogizes this to using diet and exercise to improve the performance of an athlete. The enzymes produced from Pierce’s new method reduce the response to signal compounds so that it takes a longer period of time for fruits to ripen, ultimately doubling the time.

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