Blackleg disease of canola is caused by fungal pathogens of the genus Leptosphaeria, with the species L. maculans being regarded as the most dangerous. Infections occur after spores from previous years’ stubble are released, with spores being carried by wind or rain splash to the host plant. After the spores germinate on the leaves of a host canola plant infection continues down to the base of the stem where severe infections cause ‘stem canker’; pinching of the stem which restricts the flow of water and nutrients to the rest of the plant, resulting in yield loss. The Canola Council of Canada warns that even moderate infection can result in a significant drop in yield – https://www.canolawatch.org/2017/09/13/seed-how-much-blackleg-before-i-need-to-think-about-rotating-resistance/

You should see solid woody tissue through the cut. If you can see pith (fibrous inner section of the stem) you’ve cut too high. Sample ten random stems, each several paces apart. Repeat in at least 3 areas spread across the field.

Look for black discolouration within the hypocotyl tissue, often appearing in a wedge pattern. If a stem looks to be infected, keep a 2-3 inch piece for testing. Allow samples to air dry overnight before packaging to avoid excessive fungal growth.

Keep notes on how many stems you surveyed, how many were infected and in which field samples were collected. This will be important when talking to your seed supplier or agronomist about variety selection. Testing will be performed on up to twelve samples per field. Make sure to package samples from each field separately.