Single-bin drenching with a postharvest fungicide is being tested. Research shows that the sooner a fungicide is applied after harvest, the more effective it is in preventing rot.

Single-bin drenching with a postharvest fungicide is being tested. Research shows that the sooner a fungicide is applied after harvest, the more effective it is in preventing rot.

DAVID SUGAR, OSU

Drenching single bins of pears with a fungicide in the orchard is a new tactic to help prevent decay in storage.

Pears have traditionally been drenched on arrival at the packing house, but it’s become less prevalent because of concerns about inoculating the fruit with spores that accumulate in the drench solution, which is captured and reused.

As a result, many pears are stored orchard-run in controlled-atmosphere (CA) storage without ever being treated with a fungicide after harvest, said Dr. David Sugar, plant pathologist at Oregon State University in Medford.

And, there’s evidence that fungicides are less effective the longer the period of time between wounding and treatment. Tests have shown that the postharvest fungicides Scholar (fludioxonil) and Penbotec (pyrimethanil) begin to lose their effectiveness when applied 21 days after the fruit is wounded, Sugar said during a Pear School presented in Yakima by Washington State University.

Sugar believes that with the trend for pear producers to store field-run pears in bins for longer periods of time, drenching in the orchard might help reduce postharvest decay. The advantage of drenching in the field is that the solution is used once and not recirculated. It is sprayed over individual bins of fruit and drips through the fruit to the ground.

The fungicide must be labeled for use in the field. Syngenta has received FIFRA section 24 (c) special local need labels in Oregon and Idaho for Scholar and hopes to obtain one for Washington this fall.  The label rate is four ounces in 100 gallons of water. A maximum of 400 bins per acre can be treated annually.

Sugar, who has been conducting trials with field drenching, said he’s not sure how feasible it would be for growers to fit field drenching into their already busy schedule at harvest, but it looks promising in terms of managing decay.

“From my point of view, decay is a serious enough problem it’s worth the expenditure of effort to do something like this,” he said.

In a trial using a prototype drencher, he treated 125 bins of Bosc pears and stored them for four months. When the treated and untreated fruit were packed on identical packing lines, 11 percent of the treated fruit had rot compared with 27 percent of the untreated fruit.

Sugar said the in-field drench provided a significant benefit, though not total control, and could be part of an integrated strategy incorporating as many effective components as possible.

Alex Cochran, postharvest technical manager with Syngenta, said the company is still evaluating the in-field drench with Scholar, and is not yet pursuing a full registration for that method. It’s a concept that has been discussed for some time, but last year was the first year of large-scale tests. The company does not plan to supply the applicator to growers, but Cochran said it should be a simple piece of equipment that growers could have built.

Cochran said the company feels that in-field drenching would be useful for pear producers who are fearful of the standard packing house drench inoculating the fruit with rot organisms. The idea is that the in-field drench immediately after harvest would be a substitute for a preharvest fungicide application. The cost is thought to be comparable, Cochran said.

Advantages of the drench include the ability to target strictly the fruit, rather than the entire tree, and to protect the fruit after it’s been handled and possibly damaged during harvest.