Scouting for Aster Leafhoppers

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.

AsterLeafhopperFromWinterWheat.JG.Graysville,MB.June24,11

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.

Respond
Have a follow-up question?

Over the Course of Time: Manitoba Canola Diseases 2009-2014

Canola is one of the most economically important crops produced in Manitoba and yield robbers such as canola diseases need to be identified in order to apply best management practices. For many years, sclerotinia has been the most significant canola disease in Manitoba. However, in recent years the prevalence (% of fields infested) and incidence (% plants infected per field) of blackleg have been increasing.

Disease incidence and severity will change from year to year based on use of genetic resistance in varieties, environmental conditions, and agronomic practices such as crop rotation and fungicide use. Annual surveys of commercial canola crops provide valuable information on the distribution of disease, impact of farming practices on severity and incidence, help agronomists and farmer prioritize where future resources need to be directed, and can provide an early-warning system that provides information on the occurrence of disease/pesticide breakdown.

For more information on the annual Manitoba canola disease survey including methods, results from 2009 to 2014, and further discussion, please view the attached poster which was presented at the 2014 Manitoba Agronomists Conference:

Over the Course of Time Manitoba Canola Diseases 2009_2014 (Kubinec et al., 2014)

For more information on canola diseases in Manitoba, and information on various types of control methods, please visit MAFRD’s website at http://www.gov.mb.ca/agriculture/crops/plant-diseases/index.html
Respond
Have a follow-up question?

Should I be worried about aster yellows in my winter wheat and carry-over of the disease into next spring?

No.

Aster yellows is spread by the aster leafhopper which feeds on a wide variety of hosts, including canola, flax, carrots, perennial landscape plants, and cereals (including winter wheat). However, the populations of aster leafhopper peaked in mid-summer this year and since then numbers have significantly declined. There is a chance that some of the insects may overwinter in Manitoba, but not enough to cause an issue with aster yellows in early spring next year. In 2013, like every year, the level of aster yellows will depend on when the populations of leafhoppers blow in from the southern US and to what extent they are infected with the disease.

Respond
Have a follow-up question?

I think I have aster yellows in my flax, can I spray anything to stop it from getting worse?

If you are already seeing symptoms of aster yellows in flax, it is too late for any control. The infection would have occurred from aster leaf hoppers that blew in from the south and were feeding 3 or more weeks ago. There are no fungicides available to control aster yellows. In field crops, insecticides are generally considered of little value in management of this disease, as research shows a single insecticide application would have a low probability of being of much value, and multiple applications (as done in horticultural crops) would not be practical in field crops. Because damage is so visible, it is very easy to overestimate the amount of damage across a field, so assess the crop carefully before making conclusions.

Respond
Have a follow-up question?

Why would my canola pods be splitting? I don’t see any insects that would cause the damage.

From what MAFRI staff has seen in the field and at the Crop Diagnostic Lab, we think that the cause may be due to aster yellows.  Look for any symptoms of aster yellows on the plant like bladder looking pods, purpling pigmentation and as the crop matures, these plants do not mature as quickly.  Aster yellows can cause seed abnormalities in late affected plants that display no other symptoms of the disease.  If in doubt, collect a sample, take some pictures and send it to MAFRI or submit a sample to be analyzed at the Crop Diagnostic lab in Winnipeg (can submit samples through local MAFRI GO office).

Respond
Have a follow-up question?