Verticillium stripe (VS) was first discovered in canola in Manitoba in 2014. Since then, the fungal species V. longisporum has been found in soils in Alberta, British Columbia, Manitoba, Saskatchewan, Ontario, and Quebec. The soil-borne fungus enters plants through the roots and moves upward through the plant via the xylem. The fungus eventually obstructs the xylem and cuts off nutrients to the plant.

The disease is often most apparent after harvest when stems are more visible. Earlier symptoms of the disease include leaf chlorosis, premature ripening, and stunting. One half of the stem may appear green and healthy while the other half looks discolored. As the disease progresses the stems become brittle, greyish in color and can peel or shred.

Figure 1. Symptoms of verticllium stripe in canola stems.

Verticillium is a late-season disease that is less damaging than blackleg and sclerotinia which develop earlier in the plant life cycle. However, fields with severe verticillium infection can cause substantial yield loss through the reduction of seed size. Plants infected with blackleg or verticillium stripe can have similar symptoms. When evaluating the cross-section of a plant, verticillium infection is more diffuse than blackleg.

• Verticillium microsclerotia are soil-borne and most effective at spreading in hot and dry conditions. In 2020 and 2021, verticillium prevalence in canola fields was roughly 30% in Manitoba and 1 to 2% in Saskatchewan and Alberta. In 2022, late seeding, coupled with higher temperatures at flowering, favored VS development resulting in high disease pressure. Favorable disease conditions, susceptible hosts, plus VS-infested stubble from the previous growing season contributed to the high incidence level and severity of VS. Limiting tillage and sanitizing equipment can help reduce the spread of the pathogen. Microsclerotia may survive in the soil for 10 to 15 years but extending crop rotations to 3 or 4 years can help lower disease severity. Rotating to non-host crops such as corn and soybean can help reduce the pathogen in the soil. Though the complete list of host crops for this disease is unknown, many Brassica crops such as broccoli, cabbage, and mustard are hosts to verticillium and if possible, should be avoided in affected fields.

Figure 2. The difference in precipitation levels across southern Manitoba from 2021 (left) to 2022 (right). Images courtesy of the Government of Manitoba.

Currently, there are no foliar or seed treatments available for control of verticillium stripe and there are no commercial hybrids considered to be resistant. However, there are differences in susceptibility between different hybrids. DEKALB^® canola hybrids are currently being tested for verticillium stripe tolerance. Early evaluations of verticillium stripe incidence and severity in disease nurseries have indicated potential tolerance present in some DEKALB^® canola hybrids. However, additional field evaluation is needed to confirm the stability of the tolerance under different environments.

Figure 3. Canola stem infected with verticillium (left), blackleg (center), and a healthy stem (right). Image courtesy of Canola Council of Canada.

Testing for Verticillium

If you are questioning whether or not verticllium is present in your field, sending plant samples to one of the following laboratories is a way to confirm this.