Spotted wing drosophila: fruit-damaging flies on the rise
Fruit-damaging flies are on the increase in at least 18 Arkansas counties and implementing a weekly insecticide spray program can be the answer, said Donn Johnson, professor and fruit and nut research and extension entomologist for the University of Arkansas System Division of Agriculture.
In just less than a month, researchers have found that populations of spotted wing drosophila, or SWD, have risen from less than two per trap per week to 93 flies per trap per week. The highest infestations are in Benton, Johnson and Washington counties, Johnson said.
The 18 counties are Benton, Calhoun, Carroll, Crawford, Faulkner, Franklin, Hempstead, Howard, Johnson, Lonoke, Madison, Nevada, Pike, Polk, Pope, Van Buren, Washington and White.
Percentage of berries infested with SWD eggs or larvae according to Johnson:
• On June 30 in Benton County, 26 percent of insecticide sprayed raspberry samples were infested with SWD.
• On July 7 at the UA research farm in Fayetteville, 83 percent of unsprayed ‘Natchez’ blackberry samples were infested with SWD.
• On July 7 in Benton County, 92 percent of unsprayed ‘Ouachita’ blackberry samples were infested with SWD. However, a week after insecticide was sprayed, the number dropped to 40 percent.
• On July 12 in NW Arkansas, 43 percent of unsprayed ‘Wye’ berry samples were infested with SWD.
• On July 14 in NW Arkansas, 100 percent of unsprayed wild blackberry samples were infested with SWD.
• So far, no SWD infestation found in samples of blueberry or grapes.
“Since it was first discovered in North and South Carolina a few years ago, this insect has caused 80 percent yield losses for commercial growers,” said Sherri Sanders, White County extension agent for the division.
A grower in Northwest Arkansas lost a significant portion of his blackberry harvests to SWD before implementing the insecticide spray program. After following a weekly insecticide spray program that started at first ripening, so far only 3 percent of his blackberries were infested with SWD, Johnson said.
The cold spring and cool early summer in Arkansas caused blackberry and raspberry harvests and SWD fly buildup to occur later than last year. “This year, the density increased later than in past years,” he said. This tiny Asian fly can increase to possibly 50-fold over several weeks in July and August with temperatures of above 80 degrees Fahrenheit.
Another reason may be that researchers in those areas are better at luring and trapping the flies, which resulted in a higher number of flies identified, Sanders said.
Spray insecticide weekly and alternate
To minimize SWD infestation, Johnson asks farmers to set fields with traps three weeks before ripening starts. Then growers need to check traps for flies weekly.
“If SWD is found and fruit are ripening, apply weekly recommended insecticides until harvest ends,” he said. Growers should re-apply insecticide after rain and alternate insecticides with different modes of action to keep the flies from developing resistance to a specific insecticide.
Improve spray coverage by thinning to open up canopy. “We are testing screens or row covers of less than 1-millimeter mesh to exclude flies from ripening berries,” Johnson said.
Remove damaged and overripe berries and place them in a bag or under black plastic sheet to heat in the sun—called “solarization”—that will prevent SWD reproduction.
Try to pick fruit every two to three days and quickly refrigerate results of any infested berries that have mostly SWD eggs under fruit skin and no larval development.
To confirm if SWD is present, growers should ask their county extension agent to mail a vial of flies from their SWD trap or mail a zip-top bag of 30 ripe berries to Barbara Lewis, AGRI 319 Department of Entomology University of Arkansas, Fayetteville, AR, 72701.
To learn more on how to identify SWD fly, how to build SWD fly trap and other information about SWD, visit http://www.uaex.edu/publications/pdf/FSA-7079.pdf and http://comp.uark.edu/~dtjohnso/Handout_SWD_30_July_14.pdf.
For more information about fruit production, visit www.uaex.edu/farm-ranch/crops-commercial-horticulture/hoticulture/fruits.aspx or contact your county extension office.