Feared plant pathogens pop up in Western Washington

Black leg and black rot, plant diseases that Washington agricultural officials have long been on-guard for to protect the vegetable and oil seed industries, appeared this month in Western Washington in separate incidents.

Seeds from an organic radish farm in Island County tested positive for black leg, according to the state Department of Agriculture. Meanwhile, black rot appeared on leaves of a brassica crop in Skagit County.

It’s unknown how either disease was introduced, Washington State University plant pathologist Lindsey du Toit said. Growers in both places reported the pathogens, helping efforts to contain them, she said.

“Both have the same repercussions for the seed industry,” du Toit said. “I was pleased to see there wasn’t an attempt to cover it up.”

Black leg is a fungal disease that infects cruciferous crops such as canola, broccoli and cabbage. An outbreak of black leg in the Midwest and eastern U.S. in the 1970s was traced to Northwest-produced seeds, devastating Western Washington’s vegetable seed industry. It had not been detected in Western Washington in recent years, according to the agriculture department.

Black rot is a bacterial disease. According to the American Phytopathological Society, black rot “must be considered the most important disease worldwide of vegetable brassicas.”

To guard against both, the agriculture department requires crucifer seeds planted in Island County and five other Western Washington counties to be tested and treated for black leg and black rot. The department extended the requirement to 20 Eastern Washington counties in 2015 after black leg was found in canola fields in Oregon and Northern Idaho.

In Island and Skagit counties, the farmers planted seeds that had been tested, du Toit said. Seeds, however, are destroyed during the test, so samples from seed lots are screened.

Du Toit said she examined plant matter that she collected from the field in Island County, but did not find black leg. The seeds had been harvested about a month earlier, and the disease was discovered in testing at Iowa State University.

Black leg and black rot can be spread in the rain or by wind. The crop in Skagit County will have to be destroyed, du Toit said.

The Oregon Department of Agriculture mandated statewide testing for black leg in 2015 after an outbreak in the Willamette Valley.

The five other Western Washington counties in the quarantine area are Clallam, Lewis, Skagit, Snohomish and Whatcom. The quarantine also covers all of Eastern Washington.