Sclerotinia stem rot infestations are high in many canola-growing areas the summer, and the disease will continue to advance even after the crop is swathed.
“Sclerotinia is showing up like gangbusters” in northeastern Alberta, according to Doug Moisey, the Canola Council of Canada’s senior agronomy specialist for the region.
Alternaria has also been reported, said Moisey, who’s based at St. Paul, Alta.
It’s too late for fungicide application, given pre-harvest intervals, but growers still have management decisions to make, the council said in a release this week.
Before harvesting crops with plants ripening prematurely from sclerotinia or alternaria damage on the pods, growers need to assess the damage and decide how best to approach harvest, the council said.
First, walk the crop and assess the level of disease damage. “Two per cent of plants damaged can look like a lot when assessing the field from the road,” Moisey said.
If the number of diseased plants and disease severity are low, don’t alter harvest plans.
If infection rates are high, growers need to determine where most of their yield is. If it’s in the healthy plants, then farmers should make harvest decisions based on what’s best for the healthy plants. That means swathing at 50-60 per cent seed colour change for ideal yield and quality.
If most of the yield is in the infected plants, then earlier swathing, at 30-40 per cent seed colour change, may be more appropriate. But make sure seeds in pods on branches and upper main stems are firm.
Diseased plants will dry down prematurely, which is why swathing earlier is recommended. The sclerotinia fungus may continue to grow on swathed canola if conditions are wet, but seeds that have reached the firm green stage or later should still mature.
When swathing diseased crops, take care using a swath roller, the council said. Lift the roller so it doesn’t pack the windrow too aggressively. This will protect the pods of those damaged and more advanced plants. Also, if weather conditions after swathing remain damp, compacted swaths can hasten development of sclerotinia in the swath.
Canola with severe sclerotinia infection can be very dusty when combined, due to the growth of the sclerotinia fungus as well as other moulds that can attack the decaying plants.
For that reason, the council recommends growers wear appropriate masks when handling severely-diseased canola.