Canola growers are strongly encouraged to scout canola fields for clubroot; particularly growers in Cavalier County.
In North Dakota, confirmation of clubroot has been limited to few localized fields in Cavalier County. However, clubroot likely occurs in more fields than currently detected and favorable conditions for disease development and symptom expression at the end of the season have opened a critical window for scouting.
Infected plants are less tolerant to warm and dry conditions because their root system has been compromised by clubroot (Fig. 1). The dry conditions that prevailed during the past several weeks have stressed canola plants with clubroot, accentuated disease symptoms and made them much more visible. As stressed plants die prematurely, patches in fields that may resemble drought-stress appear (Fig. 2). Infected roots have galls that are brittle and may disintegrate easily when plants are pulled from the ground (Fig. 3).
NDSU Extension and canola pathology personnel, with support from the Northern Canola Growers Association, are conducting end-of-season field surveys to identify infested fields, but surveyors typically scout a relatively small number of fields in each county. We suggest growers investigate ‘dry spots’, use a shovel to dig out plants, and investigate roots for galling. Growers who suspect clubroot are encouraged to contact Dr. Venkata Chapara at the Langdon REC (701-256-2582), Dr. Anitha Chirumamilla at the Cavalier County Extension office (701-256-2560) or Dr. Luis del Río Mendoza in the Department of Plant Pathology (701-231-8362) or through NDSU Extension (701-231-8363). The NDSU canola pathology program led by Dr. del Río Mendoza has the capability to perform laboratory tests to verify clubroot presence in soil samples.
Growers who know their fields are infested with clubroot should take precautions to reduce its spread to other areas. Some of these precautions include working the ground of infested fields the last and cleaning the equipment before leaving the infested fields to avoid moving chunks of dirt in it. Tillage operations, like disking, plowing, and harrowing, facilitate the distribution of clubroot resting spores from galls into the soil profile and may bring some spores to its surface; thus, we recommend using no-till practices in infested fields. Spores located in the soil surface may be spread by equipment, wind, water overflow, and on boots. When walking on infested fields, we recommend wearing disposable shoe covers to minimize transport of soil.
In the upcoming year, growers who grow canola in areas where clubroot is known to occur are encouraged to plant clubroot-resistant hybrids and consider extending crop rotations to three years with non-host plants like wheat, barley, soybeans, or corn before planting canola again.
Extension Plant Pathologist, Broad-leaf Crops
Area Extension Specialist/Crop Protection
NCREC, Minot, ND-58701
Luis del Rio Mendoza
NDSU Plant Pathology Professor