Codling moths love apples so much that they lay their eggs all over the fruit and leaves. Without careful moth control, the result is worm-infested apples and struggling fruit farmers.
However, many farmers, in northern New Mexico's heavy apple-growing region, use pesticides that may kill beneficial insects as well as the codling moth.
To find alternatives, New Mexico State University's Agricultural Science Center researchers, at Alcalde, are testing new organic and quasi-organic control methods to greatly reduce pesticide use.
"With conventional pesticides, growers can almost completely control the codling moth, generally limiting damage to less than 1% of the crop," said Ron Walser, fruit specialist with NMSUs Cooperative Extension service, who is supervising the research. "The question is, can we control the moth without harming other beneficial insects or the environment? Our research is showing there are alternative methods that are very effective."
Apple farmers must protect their orchards, because if left unchecked, codling moths can completely wipe out a harvest.
"They are the worst insects producers have in orchards, because they are specifically attracted to apples and attack very few other crops," Walser said. "The females lay their eggs on or near the apples, and when the larvae hatch, they chew their way into the fruit and destroy it. They will bore into every apple in the orchard unless you control them."
Farmers use biodegradable organophosphates to kill the moth, but if overused, those chemicals can seep into ground water, Walser said. Moreover, they kill predator mites, thrips and ladybird beetles that feed on spider mites and other harmful insects.
Farmers generally spray every seven to 21 days during the growing season, depending on the chemicals used, Walser said. However, farmers can substantially reduce spraying if they apply pesticides according to the moths mating cycles instead of the calendar, something Walser is now testing at the centers 1.5-acre experimental apple orchard.
There usually are three "flights," or mating cycles, per season, which begin when male moths fly in search of females, Walser said.
"We placed cardboard traps in the trees to monitor male flights," he said. "Once we trap one or two moths, it means a new mating cycle has begun, so we start spraying to kill larvae as they hatch."
Larvae gestation lasts up to 30 days in cool weather, but only about 10 or 12 days in the summer, so Walser adjusts application lengths for each mating cycle depending on weather.
"By spraying only during the mating cycles, we can cut chemical use in half, from six applications in a typical season to just three," Walser said. "The next step is to try to eliminate spraying altogether."
To do that, Walser has drawn on research in other states that identified the sex pheromone emitted by female moths to attract males. Walser mounted electronically controlled spray canisters, or puffers, in the orchard that automatically emit the pheromone every 30 minutes to confuse the males and disrupt mating.
"We overwhelm the environment with the female pheromone, so the males cannot find the females," Walser said.
Preliminary data show good results on the 10 trees where mating disruption is being used without chemicals. In that section, Walser counted only 37 wormy apples after the first mating cycle, or less than 1% of the fruit.
In three other 10-tree sections, Walser is spraying different organic-approved products benign to beneficial insects and the environment. He counted only 30 wormy apples in all three sections combined after the first mating cycle.
"Much more data collection is necessary, but the trials show that we should be able to control codling moths without harsh chemicals," Walser said.