Jul 10, 2018

How to fight hard-to-kill codling moths in apples

The early bird gets the worm, and growers who prepare early will have more luck catching codling moth before it damages their apples.

Insecticide sprays must be timely, based on traps tracking moth flights, and the traps need to be set well in advance. A diversity of insecticides should be chosen so that pests don’t evolve resistance to an over-used spray. And even non-chemical control techniques, such as pheromone disruption, require good planning.

Timely sprays

There’s a narrow window of opportunity to hit codling moths with insecticide sprays.

A delta-shaped trap – tent-shaped trap with pheromone and a sticky pattern – can help growers pinpoint the right time. The trap will measure when the moths begin flying and application of insecticides will soon follow. Adama Agricultural Solutions Development Sector & Insecticide Leader Diane Silcox Reynolds said it’s important to spray as soon as moth flights are detected.

“You want to be tracking and monitor your moth flights,” Reynolds said. “The moth will lay those eggs either directly on the fruit or on the leaf very near to the fruit, and those eggs hatch and the caterpillars immediately start to crawl and burrow and feed on the apple,” she said. “You have a very narrow window of when that happens. So, you want your product out before that happens.”

Avoiding resistance

Apple growers may apply insecticide with an airblast sprayer six to eight times during the season as codling moth moves through three to five different generations, Reynolds said.

Those sprays should be chosen carefully. Codling moth has a documented history of developing resistance to insecticides but cycling through different sprays with different mechanisms of action can reduce the risk of that.

Adama’s go-to spray for codling moth is Cormoran, a relatively new spray that debuted in late 2016, and has two active ingredients or mechanisms of action: Novaluron, an insect growth regulator, and Acetamiprid, a neonicotinoid that works on the moths’ nervous systems. But Reynolds recommends using a different spray for each generation of codling moth during the season and making sure the sprays have different modes of action. For example, a spraying schedule could start with Cormoran with the first moth flight, then during the second generation or brood, FMC’s Altacor, which works on the moth’s muscles, and in the third generation move to Dow AgroSciences’ Delegate, which like Acetamiprid works on the moths’ nervous systems, but hits a different site.

“If you use the same product you’re going to select for the ones that are resistant to the product,” Reynolds said. By hitting the bugs with a variety of chemicals, “you’re reducing the overall number of resistant moths in a population,” and decreasing the likelihood of the resistant bugs breeding together.

IPM options

Non-chemical controls of codling moth include mating disruption by aerosol dispensers of codling moth pheromone.

“It fills the orchard with that pheromone and so the moths aren’t able to find each other, because that pheromone is everywhere, instead of in a concentrated area where that moth would be,” Reynolds said. “They call it mating disruption because they can’t find each other to mate.”

Washington State University’s Decision Aid Systems website advises using oil sprays to kill moth eggs, and even adding codling moth granulosis virus to the oil sprays. More information is available online.

Outlook

The stakes are high for apple growers. A single worm burrowing into an apple makes it unmarketable for fresh sales and can even hurt processing sales.

“Your damage threshold is so low, that growers will still make insecticide applications,” Reynolds said. “Anytime you have a caterpillar in your apple, even if it’s for juice, that could still decrease your quality and ultimately how much you get paid.”

In the Pacific Northwest, “we would anticipate pressure to be similar to last year,” she said. “From what I’ve heard, they’re having an early spring again this year, so we would expect when you have an early spring that you will be battling codling moth for much longer in the season.”

– Stephen Kloosterman, FGN Assistant Editor