A new bait for controlling cherry fruit fly probably saved Washington State growers close to a million dollars last season, according to Tim Smith, Washington State University Extension educator for north central Washington.
The GF-120 bait, from the Dow Chemical Company, was registered two years ago. It contains the biopesticide spinosad (the same active ingredient as in Success and Entrust), combined with a yeasty, sugary attractant.
Two seasons ago, the early innovators in the cherry industry tried it, Smith said. Last season, it was widely used by organic and conventional growers alike.
“Last year, there was amazing adoption of this technology in this state,” Smith said.
The product was widely used in the Tri-Cities area, in south central Washington, and this was the first time in several years that no cherry fruit fly larvae from that area were found in cherries packed by north central Washington shippers.
Further north, there was more hesitation among growers to try the new product, he said. “We still have a long ways to go to get people confident in it.”
Just two larvae, which originated in north central Washington, were found in cherries at Wenatchee district packing houses last season. Four larvae were found at Yakima district packing houses: two came from Yakima, one from the Wenatchee area, and one came from Oregon, according to the Washington State Department of Agriculture’s Commodity Inspection office in Yakima.
Smith estimates that the bait eliminated the need for 52,000 pounds of organophosphate or carbamate pesticides statewide and cut 6,700 hours of applicator exposure to those pesticides. The amount of active ingredient in the bait is equivalent to a sixth of a gram per acre. The product is applied from a four-wheeler all-terrain vehicle, at a speed of six to seven miles per hour, rather than a sprayer.
Some growers who would have used the product last year weren’t able to because they couldn’t get the equipment to apply it.
“You could not buy a 12-volt ATV applicator machine last season,” Smith reported. He expects use to increase this year.
It’s a convenient product to use because it is relatively cheap and quick to apply by ATV. The product is squirted onto the trees, rather than sprayed, so there’s no problem with drift, and it can be applied even in windy conditions.
No preharvest interval
However, the bait does not kill the pest instantly, so growers need to apply it three to four days before they think they need to, and reapply every seven days after that. It’s a good product to use around harvest because it can be applied the same day as harvest.
The only failure reported was in an organic orchard, where the grower had cut the rate in half and made a dilute application. It rained twice during the growing season, and the grower didn’t reapply the bait.
Smith stressed that,“It needs to be put on at the appropriate rate.”
It might not be a good product in places like Michigan, where cherry fruit flies come into the orchards from native hosts outside, he warned, because it might not kill them immediately and mated females might lay eggs before encountering the pesticide-laced bait. “If you have native sources of cherry fruit fly, you should not rely on the bait,” he said.
Bittercherry is an alternate host for cherry fruit fly, which also loves tart cherries, Smith said. Adults begin flying between May 20 and 30 in Washington, with peak flight a month later. Flight ends in late July.
When the adults emerge, they graze on the cherry tree looking for feed and eating whatever they can find. Within seven to ten days, they start mating and laying eggs.
Yellow sticky traps are not very attractive to fruit fly. “If you can catch flies in the orchard on those traps that are not very attractive to the fly, you have a lot of flies,” Smith said. “Don’t rely on traps for timing, or presence or absence.”
Peak flight coincides with Bing harvest. Female flies lay eggs under the skin of the cherry, and larvae develop in the flesh. After about three weeks, the mature larvae exit the cherries and drop to the ground where they pupate. The insect needs to have fruit in the orchard in order to complete its life cycle, so in a Bing orchard, cherry fruit fly that complete the cycle must be coming from fruit left in the orchard after harvest, Smith said. With late varieties, such as Sweetheart, the fly has a chance to complete its life cycle and drop to the ground before the fruit is picked.
Generally, the larvae found in cherries at the packing house are very small because it’s usually during the last ten days before harvest that control with traditional pesticides breaks down. Harvest in an orchard can extend over a longer period now that new varieties of cherries are available, Smith noted.
“We used to get done with harvest in five days. Now it can be 10 to 15 days if you have different varieties in a block. You need to maintain your control through harvest, but there are not many things you can spray during harvest.”
Smith has always recommended a postharvest pesticide application to help stop the fruit fly from completing its life cycle. Dimethoate soaks into fruit, killing the larvae inside, but growers hesitate to use it because of phytotoxicity.
In tests on heavily infested backyard trees, Smith found the newer insecticides Provado, Assail, and Calypso relatively effective and easy on the tree, though Smith said more work needs to be done on rates, efficacy, timing, and sensitivity. He has also been testing experimental products.
Provado is already registered for use on cherries and can be used up to a week before harvest. At that timing, it would kill all the larvae in the fruit, Smith said, noting that there is no penalty for dead larvae in cherries, only live ones. However, new products might not have a tolerance in certain export markets, and growers should check with their packing houses before using them, he stressed.
Insect growth regulators are not normally used for cherry fruit fly, but Smith tested Rimon (novaluron). It did not kill the adults, but they laid sterile eggs, and hardly any larvae were found. More research will be done on this.
Some of the new cherry varieties are precocious and start to bear fruit in the first couple of years. Smith urged growers not to pick fruit from young blocks unless they’ve been sprayed.