Some cherry growers are still skeptical that the GF-120 bait can control cherry fruit fly as well as other pesticides do. However, the product is now widely used by the Washington State cherry industry, and inspectors didn’t find a single larva in fruit packed by north central Washington packing houses last season, reports Tim Smith, a Washington State University Extension educator. He says bait has been in use for the past four years and is now the most-used cherry fruit fly control product in the state.
Most growers use it, and some use only the bait, but there are still some who don’t use it at all, Smith said during the Lake Chelan Hort Day this winter. "Some don’t believe it works. We have beaten to death that it works. In the past four years, cherry fruit fly hasn’t got out of control. We have fewer finds than before."
Cherry fruit fly is a quarantine pest, and inspectors found only two larvae in Washington State packing houses during the 2007 season, Smith said. One was in the Tri-Cities area and the other in the Yakima Valley.
The GF-120 bait is not only effective, but also cheap. Smith estimated that it costs $30 per acre for a standard cherry fruit fly insecticide, plus $28 per acre for fuel, labor, and equipment costs to run the sprayer. In comparison, the bait costs less than $18 per acre, and it can be applied from a four-wheel all-terrain vehicle traveling through the orchard at six or seven miles per hour, which reduces application cost to just over a dollar per acre. Workers actually like the job of applying it, he said.
Industrywide, adoption of GF-120 has eliminated the use of 70,000 pounds of carbamate insecticides each of the last three years and resulted in 20,000 fewer hours of applicator exposure to pesticides and 233,000 fewer gallons of fuel used. It has cut the cost of cherry fruit fly control by $1.5 million annually.
Smith said he knows of only one instance where the bait did not work, and that was where the grower cut the rate and didn’t reapply after rain.
Other options for cherry fruit fly control include Provado (imidacloprid), which will also control black cherry aphid, and Entrust, the organic formulation of spinosad. However, most of the newer pesticides don’t have a long residual activity, so if there is an infested tree nearby, mature females can fly into the orchard.
Smith urged growers to be on their guard and look for nearby trees that could be hosts for cherry fruit fly. Even though growers are doing a good job of controlling the pest, there are still hundreds of heavily infected backyard trees around, he warned.
"Make sure those trees are not infected, because most of the products we’re moving to work really well on your orchard population, but they won’t work too well on a female that flies in and lays eggs."
Although a single cherry typically serves as a host to no more than one larva, Smith has seen some untreated backyard trees where every cherry was infested, and some, multiple times. In one case, fruit infestation was 170 percent. "I have never seen trees that infested," he said.
When backyard trees are treated with the GF-120 bait, even the worst infestations are usually cleaned up by the second season, Smith’s tests show.
In the past, dimethoate has been recommend as a postharvest treatment in the orchard to kill any larvae that might be in the fruit that remain on the trees, but the product is under scrutiny by the U.S. Environmental Protection Agency.
Growers would rather not use it either, Smith said, because it can damage leaves. There are other options that have the additional advantage of not exposing people to organophosphates. Provado, which kills eggs and larvae inside the fruit, is one of the better products, he reported. Assail (acetamiprid) will be labeled for use on cherries this year, he said, although in his tests it has not worked as well as Provado.