Managing apple pests
Two new pesticides control both codling moth and leafrollers.
A good pest management program targets multiple pests with the same material. It targets multiple life cycles, applies materials at the proper time, and uses a variety of techniques, says Michigan State University entomologist Dr. Larry Gut.
Apple growers have several new chemistries available for codling moth control, including the newly registered Delegate (spinetoram) and the soon-to-be-registered Altacor (rynaxypyr). Altacor has a new mode of action that targets the insect's ryanodine receptors, causing its muscles to contract and leading to paralysis and death.
"Both of these should benefit your program," Gut said, adding that they are highly effective codling moth controls and should also be good leafroller materials.
Building a program
Gut explained during tree fruit grower talks in Grand Rapids, Michigan, how to build a pest management program.
Once the pest complex has been identified, pesticides that are effective on more than one pest should be the first ones considered. Codling moth, Oriental fruit moth, and obliquebanded leafroller comprise the typical pest complex, he noted. He encourages growers to look on the pesticide labels for those that target more than one species and compare them to other pesticides.
For example, Calypso (thiacloprid) misses obliquebanded leafroller, but catches apple maggot, Gut said. That might be an option if you have apple maggot.
A program should also target multiple phases of the life cycle, from the egg to adult stages. An ovicide is needed if control is starting at the egg cycle. "Once the worm enters the fruit, it becomes much harder to control," he said.
Different control strategies and materials are needed for the four primary life stages: egg (ovicide), larva (larvicide), overwintered larvae (nematode and parasite activity), and adult (pheromone and mating disruption).
"It's beneficial if you can get more than one of the four stages working for you," he added.
Some ovicides, like Rimon (novaluron) work topically but also provide residual control with the residues being absorbed into the eggs. Older larvicides work by contact, while the newer compounds must be consumed.
Timing of the insecticide application is important, especially with the newer chemicals that work at specific life stages.
"I'm convinced that early season is a critical time in a pest management program," he said. "You can't let the populations build up."
With neonicotinyl insecticides, the best time to apply is just before egg hatch is predicted, Gut said.
Growers need to know from monitoring in their own orchard where they are at in the life cycle of codling moth and other pests. Monitoring insect activity will tell growers if they track with the standard egg hatch of 250 degree-days or if they are later or earlier than the standard.
"It could be that you don't have much of an egg hatch at 250 days," he said. "Or you may not have codling moth present.
"But you need to know your conditions and base your program on you monitoring in your orchard."
The codling moth virus is extremely lethal but very sensitive to ultraviolet light, so it doesn't last long, he noted. It's also slow acting.
He recommends using the virus to target the first generation, which doesn't build as quickly as later in the season. Growers can use low to moderate rates, and the material will still be effective.
He also suggests that orchardists consider alternating the virus with other materials. An example would be to use an ovicide, then virus, then larvicide, and then virus.
Another pest management option is to take advantage of using two different modes of activity—using Rimon (ovicide) early, followed by a delayed timing spray at 350 to 400 degree-days with a larvicide like Altacor. This treatment strategy worked very well in a Michigan State University trial, he said, adding that the treatment had no injured fruit compared to the untreated trial of up to 35 percent damage.
"If you have to control codling moth in the summer, wouldn't it also be nice to control apple maggot?" Gut mused. Several materials do both, and growers should make choices based on getting the best bang for their dollar. He noted that Calypso and Assail (acetamiprid) target both codling moth and apple maggot.
The use of mating disruption in Michigan is on the rise, he said, increasing from about 200 acres in 1997 to nearly 8,000 acres under the treatment in 2006. Michigan is following the same trend as Washington State—achieving about 80 percent of the total acreage under mating disruption—and in about the same time frame.
Though researchers are developing alternative methods of applying the codling moth pheromone, including encapsulated sprays, ropes, and pheromone "puffers," Gut said that ties are currently the best application method, but down the road there will likely be a more cost-effective way to apply the pheromone.
When using mating disruption, it's important to keep the pheromone rates up, he reminded growers. "We usually see damage on the edges of the block. You need to take a 'whole farm' or areawide approach. And the more dispensers, the better. We see more damage with fewer dispensers used."
Research has shown the magic number of dispensers per acre to be around 200 to 400. It's also a numbers game when considering how many traps to place in the orchard to monitor codling moth populations. Best is to use one trap every 2.5 acres or at least one trap for every five.
"The more you have, the more you can trust them," he said, noting that if a grower only uses one trap for every 10 to 15 acres, the trap can easily "get shut down" or overwhelmed. If a particular type of trap is catching a high number, "it's telling you that you have a high population and you need to do something."
Gut also encouraged growers to take a "whole farm" approach and treat the entire farm or area. Data showed that codling moth populations were reduced by 74 percent in an areawide mating disruption compared to nontreated areas.
Today's codling moth control has changed since the days of organophosphates. "It really is a combination of mating disruption and new chemistries," he said. "Growers are also doing more trapping with lures. They know what's going on in their orchards."