It Happened Here: Farmers use lead arsenate to combat codling moths

In the early 20th century, orchardists in the Yakima Valley and other parts of the state were dealing with a menace.

Apple orchards were plagued by codling moths, and for nearly a half century, fruit growers unleashed a chemical weapon on them that remains an environmental issue decades later.

The codling moth is a small, gray or brown moth that originated in Asia Minor, but has been a scourge to North American apple and pear growers for 200 years.

Adult moths mate and lay eggs either on leaves or growing fruit, depending on the time of year they are born. Once the eggs hatch, the larvae burrow into fruit, getting down to the core and feasting until they come out, spin a cocoon and emerge in two or three weeks and repeat the process.

If not reined in, the moths could destroy most of an orchard’s apple crop.

Lead arsenate, which was introduced in Massachusetts in 1892 to control gypsy moths, was seen as a way to combat codling moths. As a pesticide, it was long-lasting, effective and cheap.

It also had the U.S. Department of Agriculture’s blessing, and for the first half of the 20th century, lead arsenate was the go-to pesticide for codling moths. But the moths started developing resistance, driving growers to apply it in greater amounts.

Then there was the fact that harvested apples had to be put in an acid bath to make sure the insecticide residue was completely removed.

Lead arsenate use faded in the late 1940s in favor of what was thought to be a safer pesticide: DDT. But after DDT was outlawed, thanks in part to Rachel Carson’s “Silent Spring,” other pesticides have been employed, as well as pheromones to disrupt the mating cycle.

But lead arsenate continues to cause problems. Lead is known for causing neurological damage in children, while arsenic has been linked to heart disease, diabetes and cancer.

The lead arsenate applied to the orchards broke down into its respective components — lead and arsenic — and contaminated the soil. Research by Frank Peryea at Washington State University found that while the lead would usually stay put, going about 18 inches below the soil, the arsenic was more soluble with water and could spread more freely.

That became a greater problem as orchards gave way to suburban development. In Yakima County alone, 58,050 acres are potentially affected by lead arsenate contamination, according to the state Department of Ecology.

Among the parks and schoolyards where lead arsenate contamination has been found in Yakima County and remediated are Apple Valley Elementary School, Barge Lincoln Elementary School, Gailleon and Kissel parks in Yakima, and Volunteer Park in Selah.

The treatment consists of either removing the contaminated soil or entombing it under pavement or other impermeable barriers.

Ecology recently formed the Legacy Pesticide Working Group to study contamination from lead arsenate and other chemicals and set up programs for increasing public awareness and testing former orchard sites before new homes are built, as well as advising people living on former orchards about the possible risks.