Pest control is not easy for tree fruit growers, who face resistance and regulatory challenges, as well as pressure from neglected orchards. But new products recently registered, and some under development, look promising in research trials and should give growers alternative controls.
When codling moth and other pest control breaks down in the orchard, the grower response is typically “It’s my neighbor’s fault,” said Dr. Larry Gut, Michigan State University entomologist. “And the grower is right, because neglected blocks are causing damage to adjacent orchards. But some of the problem is also due to resistance to azinphos-methyl [Guthion] and other products.”
Gut reported on data collected by MSU researchers the last two years as they studied the impact of neglected orchards in Michigan on nearby commercial orchards. Nine locations were monitored, tracking eight pest species in commercial orchards adjacent to neglected ones, as well as blocks further away from the problem sites.
Pest pressure was much heavier in the adjacent blocks for apple maggot, codling moth, Oriental fruit moth, and obliquebanded and redbanded leafroller, he said.
“The bottom line is that you’d better spray a lot if you are adjacent to a neglected orchard because they are causing problems,” Gut said during the Great Lakes Fruit, Vegetable, and Farm Market Expo in Grand Rapids, Michigan.
Resistance to pesticides like Guthion can also cause pest control failure, he added. Research showed that of nine sites evaluated for Guthion resistance, only one still had pest populations that were highly susceptible to azinphos-methyl. The data showed that resistant larvae are able to tolerate residue levels that are fatal to susceptible larvae.
He also found that the insect growth regulator Intrepid (methoxyfenozide) and the pyrethroid Warrior (lambda-cyhalothrin) showed similar patterns of reduced residual activity in the resistant codling moth populations as compared to the susceptible codling moth larvae.
Tree fruit growers, preparing for the day when they lose Guthion (azinphos-methyl) in 2012, are looking for alternative pesticides that provide control.
In small plot and farm trials testing new products, Gut found that Rimon (novaluron) and Proclaim (emamectin benzoate) provided “outstanding” early season control of leafroller. He encourages growers to try these products, targeting the first generation to eliminate larvae.
For codling moth, both Rimon and Proclaim used early in the season helped reduce eggs and larvae from the first generation, thereby reducing codling moth pressure from the second generation. Weekly applications of the codling moth Granulosis virus, applied under heavy codling moth pressure, failed to prevent shallow stings and some deep entries, but survival of the first generation was very low and the second generation was virtually nonexistent.
Two new materials—rynaxypyr and spinetoram—have shown excellent activity against codling moth, Oriental fruit moth, and obliquebanded leafroller, he said.
“They look promising and should fit into our program.” Registration is expected on these two products in 2008.
Pheromone-based mating disruption is most successful when used on an areawide basis, he said. Gut estimated that 10 percent of the apple acreage in Michigan is under an areawide mating disruption program. During the three years that Michigan has had an areawide program, the number of acres involved has grown from 800 in 2004 to 2,800 acres in 2006.
Populations of codling moth during the three years have declined by 74 percent, with almost no damage in harvested fruit, compared with 6 percent damage in neighboring sites without mating disruption.
MSU researchers also tested several versions of a new hand-applied pheromone dispenser that is designed to better protect the active ingredient codlemone and release a pear ester attractant. Results suggest that the new dispenser may enhance codling moth disruption when compared to traditional dispensers because the pheromone is better protected from degradation rather than from the additive effect of the pear ester, Gut stated.