Canola School: What late-season stems can tell you about disease pressure

Harvest is already a busy time of year, but a few extra moments outside the combine or swather could make a big difference for disease management on those fields in future years, and could help explain yield dips you might see on the yield monitor.

According to Shawn Senko, agronomy specialist with the Canola Council of Canada, cutting is a great time to get out and scout for stem and root diseases such as sclerotinia, blackleg, and clubroot.

“Swathing time is the perfect time…stop, pull a plant, cut it, look at the base just above the soil line, look for blackleg. Pull that root, see if there’s any clubroot (galls) on the roots, and also check the plant for sclerotinia.”

Sclerotinia stem rot starts with late season lesions, progressing to girdled stems causing premature ripening, and straw-coloured plants in a green crop. Severely infected plants lodge and may shatter during swathing, and when split, bleached stems of plants affected by sclerotinia stem rot, show white mouldy growth, with hard black sclerotia inside.

Senko says that apothecia of those sclerotia (once grown) can be confused with structures produced by saprophytic fungi. The sclerotia to look for are tan or honey-coloured with the tops similar to a golf tea.

Read more from the Canola Council of Canada.

Blackleg

Swathing, according to the Canola Council of Canada, is the best time to scout for blackleg because the basal cankers are easy to see at this stage. Clipping the base of the stem at the top of the root, producers should look for blackened tissue, and identify the severity.

Senko says blackleg will appear as a pie-shaped blackening in the stem, with the severity based on a 0-5 disease rating scale.

Read more from the Canola Council of Canada.

Clubroot

Above ground symptoms of clubroot, according to the Canola Council of Canada, can often be confused or attributed to moisture stress or a number of other diseases (including the two others mentioned here). That’s why it’s important to look at the roots of any discoloured or dead plants.

Late season scouting is ideal for clubroot identification, but it shouldn’t be left much later than swathing, as the typical whitish galls may no longer be present. Producers can assess their stands during harvest, giving particular, immediate attention to any areas that become uprooted during swathing or straight cutting, as this may be indicative of a severely infected plant or plants with little healthy root tissue.

Read more from the Canola Council of Canada.