Submitted by John Gavloski, MAFRD Entomologist and Holly Derksen, MAFRD Field Crop Pathologist
Aster leafhoppers and other species of leafhoppers have been observed in large numbers in an individual winter wheat field in east-central North Dakota (NDSU Crop & Pest Report, May 14) At this time, aster leafhoppers have not been reported in Manitoba, and it is too early to know what the risk is for crops in Manitoba. Determining the risk will involve knowing when they arrive in Manitoba, what the populations are like, and what percent of the population carries the aster yellows phytoplasm. But it is not too early to start scouting for them in vegetation that is tall enough to sweep with a sweep net. Aster leafhoppers are small, about 2-3 mm long as adults, wedge-shaped, and have six distinctive dark coloured spots on their head (see image). Adults will readily fly when disturbed.
Aster leafhoppers can carry aster yellows, a disease caused by a bacterium-like organism known as a phytoplasma. Aster yellows can infect many crops including carrot, potato, flax, and cereals. Although canola is not a preferred host plant, aster leafhoppers will feed on it, and signs of aster yellows are quite visible in canola. Aster yellows was a significant problem for canola growers (and potentially cereal growers) in 2012. The leafhoppers blew in early and often in 2012 and had high levels of infectivity with aster yellows. The earlier a plant becomes infected with this disease, the more significant the yield effect can be. It is unknown at this time what percentage, if any, of the leafhopper population currently present in North Dakota is infected with aster yellows.
There are no economic thresholds for aster leafhopper in field crops. They are highly mobile insects that move quickly from crop to crop and new populations can blow in from the south at any time of the year.