On May 22, the University of Arkansas Extension Service confirmed that the spotted wing drosophila fruit fly, or SWD, had been caught in traps set in Pope County, meaning the pest has made its appearance in the state almost two months earlier than last year.
The spotted wing drosophila (pronounced druh-SOFF-ih-luh) is an especially destructive fruit fly because it lays eggs on ripening maturing fruit, upon which its larvae then feed, damaging marketable harvests.
Adult flies have also been found in Izard, Johnson and Washington counties. Suspect larvae were found on blueberries in Pope and strawberries in Van Buren counties on May 31, and on blackberries in Johnson County on June 7; the Extension Service is awaiting results of testing to confirm that these are SWD larvae.
Donn Johnson, a University of Arkansas at Fayetteville entomologist, says that it is important for fruit growers to be monitoring their crops and setting traps to keep tabs on the SWD in order to determine if and when they should begin spraying.
"There are a couple of things growers should be doing," Johnson said. "We have had workshops where they learned how to make the traps, a flour-yeast-sugar bait plus apple cider vinegar. They can put traps near plantings that are within three weeks of ripening. Then they move the traps as different blocks come into ripening."
In addition, growers can take samples of about 30 fruits during the first picking and dunk them into a container with 1 cup sugar and 1 quart water, or quarter-cup salt and 1 quart water. The white, legless larvae will float to the surface. In either case, any specimens found will need to be sent to the Extension Service for confirmation that they are SWD.
Instructions for building the traps and mixing the fruit-testing solutions, along with more information on the SWD, are available at Johnson's page on the University of Arkansas Research and Extension Service website, comp.uark.edu/~dtjohnso. Look under New Fact Sheets.
The spotted wing drosophila is most commonly found on thin-skinned, soft fruits. It was first reported this year on blueberries, and the next likely crops to mature are blackberries and raspberries. It is also known to infest cherries, but there is little cherry production in Arkansas.
In the event SWD is confirmed, it is recommended that growers spray once per week. For those practicing organic farming, the options are Entrust and PyGanic, used in alternating applications. Those not following an organic program can also alternate use of Mustang Max, a pyrethroidin, as well as the organophosphate Malathion, which has a low mammal toxicity.
"These all have a shorter pre-harvest interval," said Johnson, "that varies from three days for Entrust to one day or less for the others listed above. You can spray three days or one day out before you expect to harvest, and harvest on the third or next day."