Europe’s proposed limits of residues of a widely-used post harvest chemical threatens the bulk of U.S. apple exports to Europe.

Diphenylamine, commonly called DPA, is a plant growth regulator used after harvest to control storage scald on apples.

A pending European regulation to lower residues limits of DPA to 0.1 ppm (parts per million) on apples will would make it very risky to export apples to Europe, U.S. apple leaders said.

The new regulation could reduce Washington apple exports to Europe by 50% or more, said Mike Willett, vice president for scientific affairs for the Yakima, Wash.-based Northwest Horticultural Council. So far this year, Washington apple exports to Europe during the 2012-13 season totaled about 500,000 cartons through late April, he said. Organic apple exports to Europe will not be hurt by the regulation.

Eastern apple marketers were also stung.

“It’s a huge issue for anybody who wants to ship apples into the European Union, including the Southern Hemisphere,” said Jim Allen, president of the Fishers, N.Y.-based New York Apple Association.

Allen said he has been told the new restriction could start as early as January of 2014.

If the new residue limit is put in place, New York exporters won’t take the risk of shipping to Europe, he said. Even if growers don’t use DPA, the risk of cross-contamination with bins or storage rooms where apples had been treated is too great for the low residue level, he said.

U.S. trade officials have been negotiating with Europe over the past year about the issue, but Allen said there has been no progress made in changing the regulation.

In full crop years, New York apple exporters have shipped as many as 500,000 cartons to Europe.

“We have been shipping Empires to the U.K. for 20 years,” he said, noting the market’s importance in taking small-sized Empires.

Willett said DPA is widely used in apple storage and handling all around the world.

“The European action will make it very risky to export apples from the U.S. to Europe,” Willett said.

He said the chemical is persistent and remains on equipment, packing lines and storage rooms.

“DPA can be detected on untreated apples if they are handled in a facility that uses diphenylamine for other parts of the crop,” said.

Willett said packers can use other chemicals, such as SmartFresh, to control scald. But in that case, Willett said DPA provides a way for packers to avoid carbon dioxide injury.