Multiple tactics used against pest
Mating disruption, parasitic nematodes, pesticides, and mass trapping are all being tested against the apple clearwing moth.
Bill Bleasdale of Tiger Weed Management designed and manufactured a new piece of equipment he calls the Tiger Clearwing Moth Sprayer to target a new pest that infests tree trunks. The machine has an electronic eye that switches off the spray between trunk
Scientific literature from around the world suggests that clearwing moths are easily controlled with mating disruption, and that seemed like a good tactic for organic growers who don't have many options, said Dr. Gary Judd, entomologist with the Pacific Agri-Food Research Centre at Summerland, British Columbia, Canada.
A major component of the apple clearwing moth pheromone was believed to be the same as that of the peach tree borer, so, in 2006, growers in British Columbia began using Isomate-P dispensers, which are available commercially for control of peach tree borer, in an attempt to control the new pest.
Judd said that because of the insect's two-year life cycle, it is difficult to tell yet whether mating disruption worked, and he'll need to assess emergence of adults this year. However, judging by the numbers of moths found in traps, he fears that the blend of pheromone in the Isomate-P dispensers is not quite right for the pest and not pure enough to get the best attraction. Also, the dispensers are the clear twist ties that were used initially for codling moth mating disruption. Although the codling moth dispensers were subsequently improved, the peach tree borer dispensers were not.
B.C. scientists approached Pacific Biocontrol, which makes the Isomate-P dispensers, asking for a purer pheromone and better dispensers to improve the control of the emission of the pheromone. Those new dispensers will be available for small-scale experiments this season, Judd said.
Meanwhile, infested orchards are being surveyed this year to find out if they have low, medium, or high populations of the pest. Integrated pest management consultant Linda Edwards said it's thought that mating disruption might work best where the pest pressure is low, as is the case with codling moth.
By last year, organic growers in the Similkameen Valley had become so alarmed by the pest that they pooled their resources to pay for Amanda Brown, a graduate student at the University of British Columbia, to do trials in three organic orchards using the organic pesticide Entrust (spinosad) as a trunk drench, Edwards related. Entrust works on lepidopteran insects, but no one knew if it would control the new pest. "We were desperate," Edwards said. "It was a real crisis."
The pesticide was applied at the beginning of moth flight in June and reapplied weekly until the end of the flight in late July. It provided 95 to 98 percent control, she reported, whereas moth populations continued to be high in blocks that were treated with the pheromone only.
An emergency registration was granted for trunk applications of Entrust in both organic and conventional production. The next step was to find a cheaper and easier way to apply it.
"We have never sprayed the trunks of apple trees before," Edwards said. "This is a whole new thing."
Conventional growers can modify their weed sprayers, but organic growers don't have weed sprayers, she said. Bill Bleasdale, a retired farm equipment manufacturer in British Columbia, designed a sprayer especially for this purpose that can be attached to the front of a tractor to spray the trunks of two rows of trees at a time. It optically detects the trunks and switches off between trees. Bleasdale is now making the sprayers to order.
Work needs to be done to find the best timing for applications and the least number of sprays that will control the pest, Edwards said.
This season, she will observe the effect of Bt (Bacillus thuringiensis) sprays that are applied to control leafrollers to find out if they have any effect on the moth.
Karen Bedford, a research biologist with Pacific Agri-Food Canada, will test a number of conventional pesticides as trunk sprays this season, including some of the newer chemistries, and compare them with Entrust.
This spring, Dr. Lerry Lacey, an insect pathologist with the U.S. Department of Agriculture in Yakima, Washington, was busy rearing parasitic nematodes by the millions for tests to find out if they can keep the pest in check.
In May, he took them to British Columbia to apply them to infested trees. Two species of parasitic nematodes (Steinernema carpocapsae and Steinernema feltiae) were put in suspension and applied to trees at a rate of a million per tree in one liter of water. He treated 10 trees with one nematode species, ten with the other, and left ten untreated as a control.
The application was timed to target the apple clearwing moth larvae before they pupated and emerged as adults, as pupae are less vulnerable to the nematodes than are larvae.
Lacey said he hoped that the borer's holes would suck up enough of the liquid that the nematodes would be able to seek out host larvae and infect them. Nematodes enter the host via body openings and release bacteria, which kill the host.
In tests against overwintering codling moth, the two nematode species have provided good control, and Lacey said he is optimistic that they will work against the clearwing apple moth.
He said he understands that infestations in British Columbia's Similkameen Valley have become so serious that some growers are pulling trees out. He hopes to obtain some removed trees so he can study the galleries that the larvae make as they bore into the wood and learn more about the pest. For example, he'd like to know if the larvae move closer to the entry point, where the frass is, over time and how long they are in the pupal stage. "We need to know a lot more about the life cycle," he said.
In the future, he'd like to test Heterorhabditis species of nematodes, which are extremely active in seeking out hosts.
Judd said scientists are also looking at the idea of mass trapping of the insect. Last year, he identified two attractants for the female moth.
"We think if we can mass trap females in orchards and use mating disruption for the males, we might have something for organic growers," he said. "That's where the research is going."