Crop Advisor’s Casebook: Uneven canola ripening

A Crop Advisor's Solution provided from Grainews' June 10, 2014 issue

It was mid-August when I got a call from Jim, a grain and cattle producer near Warner, Alta. Jim, who rotates cereal, oilseeds and pulse crops on his 3,000 acres of farmland, was having trouble with his canola crop.

Amy Heather

Amy Heather
photo: Supplied

Swathing in canola needs to occur at the optimum stage of ripening in order to reduce green seed problems and/or loss due to shattering, but Jim wasn’t sure when to swath his crop because there was very uneven ripening occurring throughout the field. There had been a bad hailstorm at the beginning of the month, and Jim thought that might have something to do with what was going on with his canola. He asked me to come out to have a look for myself.

When I arrived at Jim’s farm, I could see obvious signs of hail damage on the north end of the canola field, such as broken branches and plant stems. However, some thing did not add up. Why, for example, did some plants appear to be completely ripened, while right next to them were plants which looked to be far from ripe? Hail damage alone didn’t explain the extremes in this field.

I knew it was unusual for hail damage to cause complete early ripening of plants, although it can cause parts of plants to ripen prematurely. Depending on the timing of the hailstorm, you would tend to see more branching in an affected canola crop, which makes it a little more difficult to stage for swathing. However, the fact that uneven ripening within the crop was even more evident in the south end of the field, where there had been less hail damage, made another explanation more likely.

There were obvious signs of hail damage such as broken branches and plant stems.

There were obvious signs of hail damage such as broken branches and plant stems.
photo: Supplied

“I assumed that I was just looking at the results of the hail we had seen a couple weeks earlier,” Jim said, adding that he hadn’t considered there might be another factor at play.

What, then, was to blame for the uneven ripening? All of the canola plants appeared to have relatively healthy, developed root systems, and I couldn’t see any size differences between affected and non-affected plants. However, a closer inspection of individual plants yielded some critical clues.

Crop Advisor’s Solution: Blackleg culprit in premature ripening

Jim is a grain and cattle producer who rotates cereal, oilseeds and pulse crops on 3,000 acres of farmland near Warner, Alta. He had called me in mid-August to talk about some trouble he was having with his canola crop.

Jim wanted to avoid yield loss due to green seed or shattering at harvest, but he wasn’t sure when to swath his canola due to some very uneven ripening occurring throughout the field. He thought a hailstorm a couple of weeks previously might be to blame, and he asked me to come out to his farm to have a look.

Jim’s canola crop did exhibit obvious signs of hail damage, such as broken branches and plant stems. It was also clear that while some plants appeared fully ripened, others right beside them looked to be far from ready for swathing. Hail damage can cause parts of a plant to ripen early, but the fact that the uneven ripening in Jim’s canola crop was even more apparent in areas of the field less affected by hail led me to suspect a more probable cause.

A close inspection of some individual plants revealed some lesions and cankers on the stems, as well as round, irregular-sized lesions on some plant leaves that were greyish-white in colour. Further examination turned up some black pycnidia fungal structures on the exterior of the affected stems. Cutting into the base of these stems also revealed some interior blackening; this appeared as an obvious black ring in some cases and was less distinct in others, although still having a girdling effect within the plant stem.

All of these findings were symptoms of blackleg, a common fungal disease in canola that can cause premature ripening. While the recent hailstorm might have exacerbated the problem by damaging the canola and making it easier for the pathogens to enter the plants, clearly the disease had been present in the crop for some time.

At this stage, there wasn’t much Jim could do to rectify the effects of blackleg on his crop. Both the hail damage and the disease took a toll on Jim’s canola yield. There was also some shelling during swathing, but thanks to some careful timing, this did not result in any downgrading in the quality of the canola crop that was being harvested.

I urged Jim to take a proactive approach in the future, since growing conditions had been favourable for the development of blackleg pressure and some careful scouting at earlier growth stages in his field would have revealed the disease sooner. Applying fungicides earlier in the growing season could have helped to reduce the blackleg infection. Jim could also choose to plant a blackleg-resistant canola variety in future years, now that he knows the pathogen is present in his fields.

Amy Heather is an Area Marketing Representative for Richardson Pioneer Ltd. at Stirling, Alta.

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