The apple maggot is slowly making its way north through central Washington’s fruit growing areas, though it is not yet established north of Ellensburg, Tim Smith, Washington State University Extension educator reported to growers at the Lake Chelan Hort Day this winter.

Apple maggot, which is native to the eastern United States, was first noticed in the Pacific Northwest in 1979 when it was found in Portland, Oregon. Since then, it has spread south through western Oregon as far as northern California and north through western Washington and into British Columbia, Canada. Smith said the insect requires cold winters to survive and its range is unlikely to spread further south. The insect also spread east from Portland along the Columbia Gorge and then north through central ­Washington.

In 1995, it reached Yakima, and two years later, Ellensburg. It is now established in those two areas. Part of Yakima County and most of Kittitas County are quarantined, along with 20 other Washington counties. For a pest to be considered established in an area, all its life stages must be found, as well as infested fruit, Smith said.

In 2000, trapping picked up a lone adult apple maggot in an ornamental hawthorn tree in the Wenatchee cemetery. In 2005, several more flies were found in the same general area. The trees were sprayed with an insecticide, and no apple maggot flies have been found in the area since. To this day, no infested fruit has been found in Wenatchee, Smith said.

In 2006, two apple maggot flies were found in hawthorn in Peshastin, some 15 miles from the Wenatchee finds, as well as one in Manson, one in the Methow Valley, and one in Ephrata in Grant County.

In 2007, four more were found in Peshastin, and ten were found five miles away in Leavenworth, though still no infested fruit was found. None were found in Manson, the Methow Valley, or Ephrata.

“In my opinion, there’s no doubt they are working their way up, and it won’t be too many years before they move out of hawthorns and become a hazard to our fruit industry,” Smith said.

Wide host range

The apple maggot is a relative of the cherry fruit fly and looks similar, apart from different wing markings. Unlike the cherry fruit fly (which infests only cherry), apple maggot has a wide host range, including rosehips, soft pears, apples, crab apples, mountain ash, and cotoneaster, as well as hawthorn.

The pest overwinters as a pupa in the ground. It develops through only one generation per year, but emerges over a long period of time and appears to be able to shift its life cycle to match its host, Smith said. For example, it emerges earlier on hawthorn and later on apple.

Quarantine worries

Although apple maggot can move into orchards from surrounding native brush, it is not likely to fly into orchards in large numbers or become a big commercial problem, he said. The main concern is the quarantine issue. In a quarantined area, the Washington State Department of Agriculture must certify that no apple maggot flies were caught within a half-mile of the orchard that produced the fruit or, if flies were found within half a mile, that inspections revealed no apple maggot in the fruit. The quarantine also prohibits moving homegrown fruit from quarantined counties to noninfested areas of the state.

Smith said growers would always need to guard against it flying into their orchard at random and laying eggs in the fruit. Most insecticides applied to target the second generation of codling moth will kill apple maggot, though oil and the codling moth virus have no effect at all, he said. Organic growers can keep apple maggot at bay by spraying Entrust ­(spinosad) frequently at low rates.

“There are options, and it’s not going to bring your business to a halt,” Smith said. The GF-120 bait, with spinosad as the active ingredient, has been extremely successful for controlling cherry fruit fly, and Smith said there have been encouraging results from using GF-120 to target apple maggot in backyard trees in western Washington.