August 17, 2022

QUIZ – Pre-harvest disease scouting

Pre-harvest is a good time to scout canola for diseases because symptoms will be advanced and easier to diagnose.  The timing is too late to manage the disease for this year, but results will help answer these planning questions: Does the field need a longer break between canola crops? Should the field be managed more carefully to prevent the spread of soil-borne diseases? Does the farm need to look at cultivars with improved resistance to particular diseases?  

This quiz describes symptoms for four diseases found in canola crops this time of year. Identify the disease based on the description. 

1. By late August, this plant disease can cause faint black vertical stripes on canola stems. Microsclerotia, which look like black pepper, form under the stem epidermis, darkening the stem. Closer to harvest, the epidermis of severely diseased plants will peel back to reveal the microsclerotia underneath. What disease does this describe?
2. This disease can cause greyish delineated lesions on the outside of leaves and stems, with pycnidia (black spots) inside the lesions. With yield-damaging levels of disease, the base of the stem (the crown) becomes woody and cankered. A cross section of the stem through this canker will show blackening inside the stem. Look for solid black sections, often pie-shaped, in the cross section. The stem can be completely black/brown in extreme cases. What disease does this describe?
3. At the time of pre-harvest scouting, plants with this disease will have stems with a bleached white appearance while other stems are still green and healthy. As infected stems dry down, they tend to shred and shatter very easily. White mouldy growth can be found with some infections, and black sclerotia bodies will form inside the stem. What disease does this describe?
4. This disease restricts the flow of water and nutrients within the plant, so that severely infected roots can’t transport adequate water and nutrients to aboveground plant tissues. This can result in wilting, stunting and possibly premature death. The disease does not cause lesions on stems or leaves. What disease does this describe?

 

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