Are Your Canola Swaths Turning Black?

Submitted by Holly Derksen, MAFRD Field Crop Pathologist

There have been a number of reports of ripe canola looking black or, in some cases, sooty. Upon closer examination, it looks as if a black mould is growing on senescing plants.

The good news, this sooty growth is caused by saprophytic fungi that only infect tissue that is already dead or dying – these are not pathogenic fungi, although they can be closely related to them. The bad news, in the fields we have been called to, the saprophytic fungi are growing on plants that are senescing earlier than other plants in the field due to the presence of disease, most notably blackleg.

So, although the black “mould” on the plants isn’t the issue itself, it can lead you into the field where you could discover an underlying problem. Once again, we recommend jumping off the swather with a pair of clippers, pulling up plants, and clipping them at the base of the stem to look for discolouration in the cross-section. You can’t do anything about the blackleg in this year’s crop, but the knowledge of its presence can help you with future management decisions. Rotation rotation rotation!!

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