2013, was characterised by a fairly wet late winter early spring. Unusual symptoms have been seen in canola crops throughout the Great Southern region. These symptoms are reminiscent of calcium deficiency - at a cursory inspection you can see "tipple- topple" and a discolouration on the developing pods.
THE FOLLOWING COMMENTS ARE FROM DAFFWA BASED ON SAMPLES FROM LOWER GREAT SOUTHERN AREA
The key diagnostic is what looks like a BL lesion on the left of the stem in this clip from photo and the petiole and pod lesions - lots of small black lesions and bleached patches where the necroses coalesce
The suggestion is that low calcium levels weaken the plant and allow the Blackleg to get a hold. So the Blackleg is an associated problem rather than a primary problem.
"The paddock in question has no previous canola history but is adjacent to the south of a wheat paddock in canola this year. A largely unaffected canola crop that was in canola 2 years ago is on the other (north) side of the wheat crop. The poor paddock has never been limed and had no calcium fertiliser for 5 years whereas the good paddock was limed recently"
There has not been such pod and black lesions etc with plain tipple topple in the past.
Occurrences like this are not usual and can often confuse farmers and advisors alike. Blackleg is a particularly virulent disease of canola and whilst some varieties carry some resistance, and sometimes fertilizer is coated with flutriafol to protect the young plants, this protection is generally confined to the first 2 to 4 months and protects against stem canker.
Just one more thing to watch out for in these damp years.
- Low calcium levels may be caused by acid soils, no Ca applied (as lime or fertilizer) Water stress or waterlogging.
- Nutrition stress (Calcium) has weakened the plant and allowed Blackleg to get a hold.
- Growers need to be aware of soil pH issues for Canola - in both top and sub-soil.