It often looks worse than it is but aster yellows is making significant inroads into canola fields this summer.
Derwyn Hammond, agronomy specialist with the Canola Council of Canada at Brandon, said Manitoba producers rarely see more than two percent of plants affected. This year, they have seen as much as 10 percent.
“With pods forming bladders and clubbed malformations at the top, (infected) plants tend to stick up above the rest at harvest, so they are very obvious,” he said.
Vegetable producers are reporting the highest numbers ever seen of aster leafhoppers, which spread the disease between plants.
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Hammond noted most areas of Manitoba have reported the disease this year, with later maturing fields the most susceptible.
In Saskatchewan, the highest incidence is found in northeastern and east-central areas where damp conditions delayed seeding and produced weedy fields.
Early seeding is one control strategy, although it doesn’t completely prevent the disease.
Aster yellows is contributing to disappointing canola yields, largely caused by heat in July that stressed the plants.
Hammond said producers are seeing smaller and shriveled seeds and fewer seeds per pod.
Taller discoloured and malformed plants are typical symptoms of aster yellows, with infected plants unable to produce viable seed.
Leafhoppers can overwinter but most blow in on wind from the south.
“The fact that they had elevated numbers this year doesn’t necessarily mean we will run into the same issues next year,” Hammond said.
The leafhoppers feed on echinacea, caraway, barley, wheat and vegetables such as carrots, peas and zucchini but typically feast on canola, said Penny Pearse, plant disease specialist with Saskatchewan Agriculture.
“They like the lush buffet of canola to feed on,” she said.
Like no other
Pearse called aster yellows a unique disease that is neither a bacteria nor a virus, nor is it caused by a fungus as are most diseases.
“It can’t survive on its own. It needs a way to transfer from plant to plant,” Pearse said.
Damage is complete and irreversible with few control options because it often occurs when the symptoms are noticed.
Many vegetable growers will spray for leafhoppers but wind can then bring a new batch to the field.
Yield loss is directly related to the number of plants affected, she said.
