Mating disruption of codling moth, using hand-applied pheromone dispensers, is working well, but other ways of dispensing pheromone are being tested, including fibers, flakes, and waxy dollops or drops.
Andy Kahn, research associate with Washington State University, said the main purpose of this approach is to see if mating disruption can be enhanced by using thousands of low-release point sources per acre, rather than the hundreds of point sources created with the standard hand-applied dispensers. The recommended rate for the fibers, for example, is 10 grams per acre, which is equivalent to about 30,000 fibers, versus 200 to 400 dispensers per acre for the standard Isomate-C twist-tie.
Pheromone dispensers are designed to mimic calling females, causing male moths to follow false pheromone trails. It’s also possible that pheromone from dispensers masks the natural female pheromone so that male moths can’t find the females.
“The idea was that you have more female mimics out there instead of this one massive twist tie putting out an unnaturally strong plume,” Kahn said.
It’s also thought that growers might be more comfortable using products that can be sprayed on trees, rather than those that have to be individually attached to the trees, and manufacturers say products that can be applied mechanically can reduce labor costs.
Michigan State University entomologist Dr. Larry Gut, who is also studying new ways to apply pheromone, thinks increasing the number of point sources is a step forward, though more research needs to be done to establish just how many are needed for the best disruption of mating.
The fibers, made by Scentry Biologicals, Inc., are tiny hollow tubes containing pheromone, which is released over a long period of time by capillary action. The fibers are mixed with Biotac adhesive and applied through a machine that uses centrifugal force to blow them into the tree, Kahn said. The machine is mounted on a tractor, and a shroud protects the driver from the fiber mixture. Alternatively, the fibers can be applied by air.
Two types of fibers have been developed—a long one, measuring about 1.5 centimeters, which is registered for use now, and a shorter one, which is designed to create more point sources of pheromone per acre. The long fibers last for an entire generation of codling moth and are applied twice per season in the Pacific Northwest. The unanswered question is whether the short fibers will be as long-lived, said Kahn. The advantage would be a 50 percent increase in the number of point sources compared to the longer fibers.
In small-scale tests last season, he found no difference in efficacy between the long and short fibers, however.
Gut said the shorter fibers might be easier to apply and stick better to the tree than the longer ones. He expects the short fibers will last long enough to cover one moth flight.
The Disrupt MicroFlake from Hercon Environmental was approved by the U.S. Environmental Protection Agency during the 2005 season. This will be its first full season of use. The original applicator used a dilute adhesive, which was sprayed into the air flow created by a leaf blower at the same time as flakes were blown into the air stream and out into the canopy. The recommended rate is a pound per acre, which contains 22,650 flakes.
Kahn found that 40 percent of the flakes fell off the tree in the first day because they didn’t get mixed with the adhesive and were dry. Sixty percent had fallen off after three weeks. Even so, Kahn saw 73 percent trap shutdown in the moth’s second generation, compared with untreated plots.
Gut said even fewer flakes stuck to the trees in tests in Michigan. In his opinion, it doesn’t take a lot of pheromone to get 60 to 70 percent trap shutdown, but for good codling moth control, there should be almost complete trap shutdown, and achieving higher levels of shutdown becomes much more difficult.
“When you get 60 to 70 percent trap shutdown, there’s some impact on codling moth populations, but it’s really not where you want to be,” he said.
The target should be at least 50 flakes per tree, Kahn said, and 100 would be preferable.
Kahn said the application method has since been improved. Now, the flakes are mixed with an undiluted adhesive in an augur so they are thoroughly coated before being pushed into the air stream and up into the top third of the tree. The Microtac adhesive is washable while wet, and is easy to work with, but sticks fast when dry, Kahn said. In tests with the new application method, only 9 percent of the flakes were lost after 19 days.
“We’re excited about the improvement with the new Hercon applicator,” he said. “With improved application, we may be able to use lower rates with the flake and, if they are up in the tree, get better results,” he said.
Jim Nelson, Hercon’s business development manager in the Pacific Northwest, said the product was widely tested last year, and he expects that in 2006 it will be used on between 3,000 and 5,000 acres out of the 100,000 acres in Washington State that are treated with mating disruption. The applicator can be mounted on a four-wheeler vehicle, which means that it can be driven through the orchard at eight to ten miles per hour. It would take only 15 minutes to treat 10 acres. All product distributors should have applicators and be able to offer custom applications to growers.
The product can also be applied by helicopter.
The company has developed another pheromone flake for control of oriental fruit moth.
Probably the biggest issue with the microdispensers is that they can’t be applied until there is enough foliage on the tree for them to adhere to, Kahn said. Whereas supplemental sprays are an option with the hand-placed dispensers, they are a requirement with the microdispensers, because some moths will mate before the product is applied.
“We have a lot of growers with low pressure who can put up 200 dispensers per acre and not do another thing for codling moth,” Kahn said. “That option would not be open to you with these microdispensers, unless your population is so low you’re not concerned about a small proportion of mating.”
The delayed application goes against all the advice growers have been given when using standard dispensers, which should be applied at full bloom before the moths are active.
“Now we’re taking a whole new twist on that,” Kahn said. “You don’t want them all to end up on the ground.”
Gut said when the fibers or flakes are applied around bloom, some stick to petals and fall off the tree at petal fall.
But Kahn said many growers count on doing a supplemental spray anyway, and if they have leafroller problems, Intrepid (methoxyfenozide) at petal fall will kill codling moth eggs as well as leafrollers at that time. Alternatively, Rimon (novaluron) is a good ovicide and larvacide for codling moth, he said.
“It might not be such a disadvantage to have that delayed application. You’ve got to control your leafrollers, regardless.”
Kahn said more experience is needed with the products, and he plans to test them on a larger scale this season. One of the questions still to be answered is how well the microdispensers need to be distributed in the canopy. Should they be targeted at the tops, like hand-applied dispensers, or should they be distributed throughout the canopy?
Gut said he’s been using a paraffin wax-based product invented at the University of California-Davis in research designed to answer such questions. The product has been commercialized by ISCA Technologies, which calls it SPLAT (specialized pheromone and lure application technology). It contains glue so that it sticks to the tree when it hardens, and can be used with pheromones for mating disruption or for attract-and-kill programs.
At first, wax containing the codling moth pheromone was applied in big dollops, using a spatula. Agricultural engineers at MSU have since developed an applicator, somewhat like the one used to apply fibers, so it can be applied in large drops and create more point sources—up to 130 per tree.
Gut is experimenting with pheromone protectants and looking at how much pheromone is being released from the drops, how big they should be, and how attractive they need to be to get the best control of codling moth. Gut said wax is an easy formulation to work with, and the results of his tests could be useful in optimizing other pheromone delivery systems, such as the fibers or flakes.