Alternaria black spot

  • Lesion ID

    Alternaria black spot

    Learn to tell the difference between common lesion-causing diseases — blackleg, sclerotinia stem rot and alternaria black spot.

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  • Disease update: Sclerotinia, clubroot, blackleg, alternaria

    Alternaria black spot

    Sclerotinia stem rot

    Lots of sclerotinia stem rot. As harvest progresses, we’re hearing reports of higher levels of sclerotinia stem rot in some regions. Some fields that did not get a fungicide spray are at 40-50% infection. That works out to an estimated 20-25% yield loss, or 10-13 bu./ac. on a canola crop with 50 bu./ac. yield potential. Fungicide applications for sclerotinia stem rot may not provide a return on investment every year. But if conditions leading up to flowering suggest an elevated risk, spraying is warranted. Conditions after flowering are almost impossible to predict, so we can’t predict sclerotinia stem rot severity at flowering. But using the example above, one properly-timed spray can pay for 10 years worth of fungicide applications.

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  • Hail at flowering

    Alternaria black spot

    Yield loss will be lower if hail hits before flowering than at late flowering. Source: Canola Growers Manual

    Canola is quite resilient to light hail at up to 20% flower. The crop can flower longer to compensate, and may recover with only minimal to moderate yield loss. Canola has also shown remarkable recovery from more intense hail at 20% flower. However, a crop flattened by hail is unlikely to recover. If regrowth occurs, which is possible, plants are set back so far that maturity becomes a major factor.

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  • Diseases to look for while harvest scouting

    Alternaria black spot

    Pre-harvest is a good time to scout for disease severity. The photo above shows severe sclerotinia infection. This article includes sclerotinia and various other diseases to look for.

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  • Pre-harvest scouting for disease

    Alternaria black spot

    Pre-harvest is a good time to scout for disease severity. Fields with lots of diseased plants may also be poorer candidates for straight cutting due to the increased shattering risk. Read more for tips on how to identify blackleg, sclerotinia and alternaria.

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  • Alternaria can make hailed pods brittle

    Alternaria black spot

    Alternaria has infected the pods of many hailed crops. Keep watching these crops. When infected areas make up 50% or more of the crop, swathing early may be the best way to salvage the yield in those infected plants if a large proportion of pod surfaces are covered with the black spots. Read more to see photos of alternaria infection.

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