A new wax product that is sprayed on trees to prevent rain cracking can reduce losses by half, says the Washington State University researcher who invented it. But to be effective, it must be applied weekly during the month before harvest.

Dr. Larry Schrader, horticulturist at WSU’s Tree Fruit Research and Extension Center in Wenatchee, said that the product, which is called RainGard, can’t just
be applied when the weather forecast ­predicts rain.

When developing the coating, Schrader tested one application, then two, and finally found that four applications gave the best results. The surface area of a cherry expands very rapidly, and at a much more dramatic rate than its diameter. The RainGard coating is made primarily of carnauba wax, which doesn’t have a lot of elasticity, Schrader said. "So, it doesn’t stretch like a rubber band. It needs to be replenished."

He recommends that product be first applied a little before the cherries turn straw color. It should then be reapplied weekly until harvest. The fresher the application when it rains, the more effective it is, because the cherries just keep expanding, he said. Growers can use weather forecasts to adjust the timing of their applications for the best results.

The material costs about $35 to $40 per acre per application, and Schrader said he understands growers’ concerns about the cost of multiple applications. However, he tells growers to think of it more as an insurance policy, knowing that some year their orchard is likely to be hit by rain.

"It’s an investment of a couple of hundred dollars

[per acre], but if you’re looking at a $10,000 crop or more, it’s a fairly inexpensive insurance."

RainGard is widely used in the cherry-growing area of The Dalles, Oregon, where growers tend to lose cherries to rain every year, he reported.


RainGard is a modification of Raynox, a product that Schrader developed earlier to control sunburn on apples. When he first became interested in developing a product to prevent cherry splitting, he tested Raynox. It reduced the amount of splitting, but the treated cherries didn’t have a nice luster. He modified the formulation so that the new product helps give the cherries a nice shiny appearance.

Raynox and RainGard are owned by the WSU Research Foundation and were licensed to a company called FruitGard, LLC, that Schrader formed with a partner.

Pace International, LLC, which has been the exclusive manufacturer and distributor for Raynox and RainGard, acquired FruitGard, LLC, in January of this year and is now the licensee for both products.

A U.S. patent was granted for RainGard in 2007. WSU will continue to receive royalties from the sale of the two products, and will use the income to fund research on innovative technologies.

Pace, which is based in Seattle, Washington, is planning to expand use of Raynox beyond apples to include a variety of fruits and vegetables that are prone to sunburn, according to a press release from the company.