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Doug and Len England, owners of Custom Orchard Fumigation in Manson, Washington, recommend fall fumigation, though there are good reasons why a grower might prefer to wait until the spring.

The Englands, who apply Telone C-17, prefer fall fumigation because the fumigant sits in the ground over the winter and gradually vaporizes over a matter of months. The fumigation can be done any time from soon after harvest until the temperature of the ground at a depth of 18 inches falls below 42°F.

“Some growers will have the excavator scheduled for the day after they pick,” Doug said. They know which blocks they’re going to remove and are ready to replant.

Typically, the Englands can fumigate until Thanksgiving and some years as late as December. With cherries, which are harvested earlier, the window for fumigating is longer than with apples.

But other growers prefer to wait until spring. They might want to take time off after harvest, or wait to see how their low-color Fujis pack out, or find out if the market is going to rebound on a low-paying variety before deciding which block to replace, Len said. “Some years, people wait to see if they’re going to make any money. They’re committed to a certain number of trees, and they know they’re going to replant something, but they’re not sure which block.”

Spring fumigation can’t be done until the snow melts and the ground warms up to 40 degrees at 18 inches. Dale said when the ground starts to green up, it’s a sign that it’s close to the right temperature. Typically, the Englands begin fumigating in late February in the southern parts of Washington.

The window for spring fumigation is narrow because the trees can’t be planted until about a month after the fumigant is applied, and most growers are anxious to get their trees in the ground. The fumigant must be left sealed in the ground for about ten days to two weeks, and then the ground must be worked and opened up for two or three weeks more so the fumigant can vent out and dissipate. This ­additional ripping makes spring fumigation more expensive than fall fumigation.