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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect Update

August 24, 2009                  

Compiled by: John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives, Crops Knowledge Centre,
Phone: 204-745-5668; Fax: 204-745-5690

To report observations of insect activity or control that may be of interest or importance to others in Manitoba, please send messages to the above contact addresses.

To be placed on an e-mail list so that you will be notified immediately when new Manitoba Insect Updates are posted, please contact John Gavloski at the address or numbers listed above.


Grasshoppers are of concern in localized areas. Levels of soybean aphids have increased, but remain well below the economic threshold.

Recent Insect Concerns and Observations

Grasshoppers: Some localized high populations of grasshoppers continue to be of concern . Reports from the past week include high populations being noted in canola, and in flax in eastern Manitoba.

One of the questions from the past week was what options are available to control high grasshopper populations in swathed canola, or other swathed crops. The answer is nothing, which is why it is important to be checking grasshopper levels earlier in the season. If we use canola as an example, the shortest preharvest interval for any insecticide used to control grasshoppers or any other insect on canola is 7 days. The preharvest interval is the number of days that must pass between the last application of a pesticide and the cutting of the crop. So it is the time that must pass before the crop can be swathed, not the time until combining (except for direct-combining). So insecticides can not be applied to a swathed crop, and in the case of canola cannot be applied within 7 days of swathing.

Soybean aphid update: Soybean aphid levels have increased in some fields, but are still not approaching economic levels. Some fields have patches where the aphids are quite noticeable on the plants, but overall the fields are well below the economic threshold, which is when there are at least 250 aphids per plant on average, and the population is still increasing, and the plants are in the beginning bloom to beginning seed growth stages.

Sunflower Insect Update: Populations of insects that feed on sunflower seeds are generally relatively low. Data from the pheromone-baited traps for banded sunflower moth show that weekly counts continue to increase in most areas, indicating that emergence and flight are still building or peaking. Counts have generally been higher so far in traps further west in the province, than traps in more eastern areas. Highest cumulative counts so far are from fields near Waskada (517), Glenwood (471), Treherne (352) and Altona (324). There have been no reports of seed weevils at concerning levels; in most fields they are hard to find at all.

Preventing stored grain insects: A reminder before moving and storing new grain to clean old grain out of bins, augers, combines, truck beds, and other areas where grain or grain debris may be. Infestations of stored grain insects such as rusty grain beetles do not get started by harvesting the insects along with the grain. They are the result of insects already being present in bins or equipment used to move grain, or insects being able to get into the stored grain through openings in bins or storage structures. Below is a picture of a sawtoothed grain beetle (top right), red flour beetle (bottom left), and rusty grain beetle (bottom right) with a grain of wheat (top left) to give perspective on size.

Stored Grain Insects

Surveys and Forecasts

Grasshopper Survey: A reminder to farm production advisors and others involved in the grasshopper survey, that this should be completed by the end of August. Grasshopper populations are estimated in August, when egg-laying is normally occurring, to determine the risk for grasshoppers damaging crops the following year. Factors such as temperature and rainfall are accounted for when the forecast is written. A reminder that if grasshopper levels are high it is not possible to get exact counts as grasshoppers jump through the vegetation as you approach. Estimates are all that is required, and in many cases all that is possible, for the survey.