Jul 10, 2017

Brassica black leg alert issued in eastern Washington

Black leg is reportedly present in multiple counties in eastern Washington. Washington State University Extension issued an alert for growers of seed crops of all kinds of brassicas (radish, canola, kale, mustard, turnip, etc.), as well as cover crop seed producers and growers who utilize brassica cover crops in the Columbia Basin.

Black leg of brassicas is caused by the fungus Phoma lingam (Leptosphaeria maculans and Leptosphaeria biglobosa) which can be seedborne and seed transmitted on almost any genus and species in the Brassicaceae. For some brassica crops, particularly vegetable brassicas and brassicas under certified organic production, there is a zero tolerance for seed lots infected with this fungus. The Columbia Basin of central Washington is a very important region for production of seed crops of diverse types of brassicas, including seed crops of winter and spring canola, seed crops for brassica cover crops (e.g., seed crops for mustard cover crops), and seed crops of diverse types of vegetable brassicas (radish, kale, turnip, etc.). Therefore, it is very important to keep the black leg pathogen out of the Columbia Basin in order to protect the high value brassica seed industry in this region.

The increasing prevalence of black leg in regions around the Columbia Basin calls for diligent scouting of any kind of brassica crop in the Columbia Basin to assess when/if the disease has moved into the Columbia Basin, so that relevant management practices can be implemented promptly to prevent or limit establishment of this disease in this seed production region.

The Washington State Department of Agriculture has a Crucifer Quarantine ruling that was implemented at the request of the brassica (crucifer) seed industry and other crucifer stakeholders to try and protect against losses to black leg in this state. Under this rule, any brassica (crucifer) seed to be planted in any county east of the Cascade Mountains, or in any of six counties in northwestern Washington, must have been tested for the black leg pathogen and certified to be ‘black leg-free’. A green WSDA tag should accompany any brassica seed lot to be planted in these regions of the state, including cover crop seed lot or seed mixtures.

If you observe suspect black leg symptoms in any kind of brassica crop in central or eastern Washington, including cover crops, place dry leaf, stem, pod, or other symptomatic plant tissue in ziplock bags, mail the sample(s) by overnight shipment to the WSU Pullman Plant Diagnostic Lab, and provide relevant details on the crop on the sample submission form to the Washington State University Pullman Plant Pest Diagnostic Laboratory.

Visit the following links for more information on black leg or visit http://extension.wsu.edu:

• Images of the disease can be found on the Pacific Northwest Vegetable Extension Group Photo Gallery at http://mtvernon.wsu.edu/path_team/brassicaceae.htm#blackleg
• PNW Disease Management Handbook sections on brassica black leg https://pnwhandbooks.org/plantdisease/host-disease/seed-crop-crucifers-brassica-raphanus-spp-black-leg (in the search option, indicate the type of brassica crops of interest to you to get the relevant information for specific types of brassica crops)
• PNW VEG Brassica IPM Resources section at http://mtvernon.wsu.edu/path_team/ipmResources.htm#brassica