Unique conditions | Disease arrived in 2012 with leafhoppers carried into the Prairies by unusual winds
BRANDON — Farmers don’t need to worry much about a recurrence of last year’s aster yellows outbreak that significantly reduced canola yields.
The outbreak was brought on by unusual south winds carrying unusually infected bugs, conditions that don’t prevail in most years.
“It’s not like our blackleg or sclerotinia that we know we’re going to see every year. This is something we might or might not see,” Canola Council of Canada agronomist Angela Brackenreed said in a presentation during Manitoba Ag Days.
“Blackleg and sclerotinia are probably more important to be putting our time and research dollars into.”
The 2012 aster yellows outbreak was caused by “waves of leafhoppers that moved in from the U.S.,” Manitoba Agriculture pest specialist John Gavloski said at St. Jean Farm Days.
“It wasn’t so much the overwintering leafhoppers,” he said. “Really, the problem was the waves of leafhoppers.”
Aster yellows is caused by a disease carried by the aster leafhopper. The insect feeds on plants that then get infected with the disease, causing pods to become sterile and often shriveled, purplish and paddle-shaped.
Gavloski said waves of leafhoppers began appearing in the southern United States in early April. They were found in South Dakota in early May and soon in North Dakota as well. They appeared in Manitoba in late May and were soon found in many parts of Manitoba and Saskatchewan.
The tiny insects are carried large distances by the wind, and under the right conditions can easily move from the southern U.S. to the Canadian Prairies. The conditions were right all summer, with repeated waves bringing in new infected bugs.
The insects were also highly infected with the aster yellow disease. Usually only one to four percent of aster leafhoppers have the disease, but in 2012 it was 12 percent and higher.
Brackenreed said that makes it difficult to control by insecticide spraying.
Anecdotal evidence suggests fields with many grassy weeds had greater problems than clean fields. Brackenreed said the disease and insect can overwinter in grassy weeds, so getting rid of those is one possible way to lower the risk of an outbreak.
He said aster yellow outbreaks can be underestimated because sometimes only one of three or four infected plants shows visible signs. That means a field that appears to have a 10 percent infection rate could have 30 to 40 percent.