Moths scourge of orchards

Photo: Wikimedia commons

A codling moth larva in its infested apple.

The fight against codling moths, the scourge of apple growers up and down the Okanagan Valley, is continuing with some good news and some bad presented to the Regional District of Okanagan Similkameen board Thursday. 

The Okanagan-Kootenay Sterile Insect Release program has been operating for 30 years. They use a combination of mating disruption and sterile moth releases in orchards from Salmon Arm down to Osoyoos to control the moths who are fond of burrowing larvae and feces-filled holes into pome fruits like apples. 

General manager Melissa Tesche said they oversee 1,725 orchards encompassing 8,135 acres throughout the Valley, 45 per cent of which are on RDOS land. The overall number is a significant drop from when they began with 22,000 acres 30 years ago, much of which has gone to grapes and sweet cherries. 

But the moths are a big issue for the remaining apple orchards, exacerbated by climate change. 

"We have some orchards that have really serious problems," Tesche said, pointing to Summerland, Penticton and Naramata in particular. 

Tesche said increasing numbers of above-average warm days during the growing season are perfect for the moths. 

"If it dips below a certain temperature, moths don’t fly, caterpillars don’t crawl around,” she explained, adding that in recent years, not enough cool weather has prevailed. “You might get enough degree accumulation through a summer that you might get a whole extra generation of codling moth.”

Each extra generation quadruples the population of the one before it. 

Tesche said the program's goal for each orchard is for every thousand pieces of fruit picked at the end of the year, fewer than two should have moth damage. This past year, 86 per cent of orchards met target damage level, but the ones who didn't often failed by a lot. 

Tiny orchards, at less than one acre, saw the worst damage. 

"The worst one per cent of orchards have 25 per cent of all the wild moths captured," Tesche explained. 

A warming climate is one problem, but another is what Tesche termed the "pome fruit perfect storm." She said small hobby orchards are becoming increasingly common, often purchased by people who don't know much about farming but like the idea of selling a few organic apples at farmers markets.

"Frankly, they could do that, and sustain 10 per cent damage, and still make some profit," Tesche said.

"So I'm empathetic to those people who might find themselves on the receiving end of a compliance order because they don't need only two-fruit damage, but the commercial farmer down the road does, and those moths don't respect property lines."

Another issue is orchardists selling firewood at the end of the season for a bit of extra cash. Tesche said she understands the impetus, but scrap branches and wood should be burned or chipped because they may contain moth larvae. 

Tesche also had some good news. When the program first began, there were concerns that Washington State orchardists weren't following any similar program, which could potentially negate any progress made in the South Okanagan. Washington favoured spraying, a chemical-heavy process that also has not proven very effective.

“It’s the number one pest for a reason, it’s not responding well to chemical control,” Tesche said. 

But now, Washington is getting on board with sterile moths and mating disruption. For the first time in 2019, farmers there purchased moths from the Sterile Insect Release program, meaning profit in their pockets to continue the fight at home. 

Tesche said she has already gotten a request from them for "as much as we can produce for them for the next year."