Flies caught at 15 Methow Valley orchard sites in 2015

Photo courtesy of Joseph Berger, Bugwood.org via Wikimedia Commons A female apple maggot fly.

Photo courtesy of Joseph Berger, Bugwood.org via Wikimedia Commons

A female apple maggot fly.

By Ann McCreary

The capture of 32 apple maggot flies in Okanogan County last summer — most of them in the Methow Valley — is a worrisome development for the county’s head pest control official.

Each summer the Washington State Department of Agriculture (WSDA) places fly traps in apple trees around the state to survey for the presence of apple maggot flies, in order to provide early detection and control of a pest that can pose a serious threat to the commercial apple industry.

Since 2011 no flies have been caught in Okanogan County. In 2015, however, flies were caught at 18 sites, 15 of them in the Methow Valley.

The surveys have been conducted since the early 1990s, and the first detection in Okanogan County was in 2005 in the Twisp area, said Dan McCarthy, Okanogan County Pest Control Board agent.

“There was one fly [in 2005]. We’ve had a couple others since then, but none recently. So it was kind of alarming. We went from several years with no detection at all, and all of a sudden we had 18 positive trap sites in Okanogan County in one year,” McCarthy said.

Currently all of Okanogan County’s 28,000 acres of commercial apple orchards are free of apple maggots, McCarthy said.

Female flies lay their eggs in apples by puncturing the skin of the fruit. The eggs are laid in late summer and hatch within a week into larvae that burrow through the fruit making it brown, mushy and inedible.

“It’s a native pest in North America but has not been established in Okanogan County. The west side of the Cascade divide is all quarantined, it has been for some time, because of the established apple maggot populations there,” McCarthy said.

46AppleMaggot-BoxIn areas under quarantine, commercial apples must be inspected and certified as pest-free before they can be shipped out of the area, and homegrown, uninspected tree fruit cannot be taken out of the quarantine area.

County and state pest control agencies will be watching the results of this year’s apple maggot fly surveys to determine whether the flies caught last year signal an infestation, and whether measures such as quarantines need to be taken to protect Okanogan County’s $250 million tree fruit industry, McCarthy said.

“After the 2016 apple maggot survey we’ll have an indication as to whether it was an anomaly,” McCarthy said.

“Maybe the survey will come up with nothing this year and the red flags will go down,” he said. “The big concern is if the pest becomes established, the county could become quarantined, in which case fruit would have to be inspected before it could be shipped from the county.”

Traps around county

About 300 apple maggot fly traps were placed throughout Okanogan County last year. The sticky traps are placed in apple trees at residences, farms and orchards at the beginning of August and remain in place until September.

McCarthy was notified in mid-September that flies had been found in 18 sites. The 15 sites in the Methow Valley extended from the Carlton Bridge “all the way up the Chewuch” drainage, McCarthy said. They represented 14 different properties, because one location had two positive traps.

The other positive sites include one in Pateros, one near Loomis, and one in Okanogan. The site near Okanogan was within one-half mile of a commercial orchard, which means the orchardist will need an inspection by WSDA to certify the fruit is pest-free before it can be shipped out of the county, McCarthy said.

In some counties, apple maggots have been confined to small areas through partial quarantines that affect only a portion of the county, he said.

After they were found last summer, the flies were sent to a state lab for positive identification, because apple maggot flies are almost identical to snowberry maggot flies.

State agriculture agents collected fruit at each positive trap site and sent it to a “rearing facility” to determine if the larvae in the fruit continued their life cycle, which would indicate a reproducing population, McCarthy said.

The results showed that the population was not reproducing, which was good news, he said. This summer the state will increase monitoring in the areas of concern.

“During the next trapping season they [WSDA] will put multiple traps at each of the positive catch sites,” McCarthy said.

McCarthy said he attempted to contact property owners at all the positive trap sites to discuss pest control. Under state law, property owners have a legal responsibility to manage insect pests in their trees.

However, it is not always easy to locate property owners, especially in the Methow Valley where so many homes are not primary residences, McCarthy said.

One of the sites in the Methow Valley was the same one that had a positive trap in 2005, and the tree had been sprayed at that time for apple maggots. The owner lives in the Puget Sound area, he said.

“Some people have little backyard orchards and are interested in growing fruit for their own use. Others have abandoned, feral trees,” McCarthy said. “In a lot of cases it’s nonresident homeowners and they’re not around to take care of their trees and they may not care.”

Responses from residents he was able to contact ranged “from people interested in doing what they need to do, to people who weren’t interested in taking any action. Some people just said, ‘Oh well,’” McCarthy said.

The upper Methow Valley has an abundance of hawthorn bushes, which are a preferred “host plant” for apple maggots, McCarthy said.

Control and compliance

The pests are fairly easily controlled by spraying trees with pesticides, McCarthy said. The spraying is usually timed to coincide with fly activity near the end of July and requires repeated applications.

“It takes effort. It’s something you do because you like the fruit. You want some nice apples,” he said.

Pest control officials have the ability under state law to force compliance, although that is rarely pursued, McCarthy said.

It requires notifying property owners that they must control pests, summoning them to court if they don’t, demonstrating that the property owner’s failure to eradicate pests is a burden to the tree fruit industry, and obtaining a ruling from a judge. The whole process can take up to three years, he said.

“I can hire someone to come in and spray the trees, or cut them down,” McCarthy said. The process has been used most often in the case of abandoned orchards that are not being maintained.

“We hope everyone is compliant and takes care of their pest problems,” he said.

The easiest way to control apple maggots is to “avoid planting or growing apple trees in your backyard,” according to a bulletin from the Washington State University Extension program.

To help homeowners get rid of backyard apple trees that they don’t want to care for, Okanogan County offers free tree removal and a $25 certificate for an ornamental plant, McCarthy said. For information, call (509) 322-1286.

As a small, commercial grower himself, McCarthy said the financial and logistical burdens posed by quarantines, inspections and eradication of apple maggots are something everyone in the Okanogan County tree fruit industry wants to avoid.

“If you’ve ever been involved in a harvest, you hit the deck running and you don’t stop until it’s over,” McCarthy said. Any delays in the process of getting fruit to market as a result of pest inspections can adversely affect the quality of the fruit, he said.

Washington’s apple maggot control program has proved successful in protecting the state’s biggest cash crop, McCarthy said. 

“There has never been a commercial crop of apples in Washington state infested with apple maggots,” he said.