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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect Update

August 17, 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.

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Summary

Aphid levels continue to be a concern in several crops, including cereal crops and canaryseed. Low levels of soybean aphids have been found in soybeans. Lygus bugs in sunflowers and grasshoppers are other insects of concern.

Recent Insect Concerns and Observations

Aphids in cereals: High population of aphids continue to be noticed on some cereal crops. At this point in the season it should just be crops seeded quite late where there may be concern over economic damage. The economic threshold for aphids in cereal crops is 12-15 per stem prior to the soft dough stage. Once cereal crops reach the soft dough stage aphid control is no longer likely to be economical.

Aphids in Canaryseed: Some canaryseed fields in the Central region of the province have had insecticides applied to control aphids. The species that are of concern in canaryseed are some of the same species of concern in cereal crops; mainly English grain aphids and bird cherry-oat aphids. Aphids are often hidden in the heads or under leaf sheaths in canaryseed, so remember to check these areas. A nominal threshold for aphids in canaryseed is about 10-20 aphids on 50% of stems prior to soft dough.

Soybean aphid update: Those scouting soybeans have noted that soybean aphids have been found over the past week in several soybean fields in the eastern part of the province. However, the soybean aphids are at low levels, well below economic threshold, and at this point farmers and crop scouts have to look hard to find them. Most plants having none with the odd plant having small colonies. The economic threshold for aphids in soybeans 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. So soybeans fields are a long way from even being close to having levels of soybean aphids that potentially could be economical. Keep checking for soybean aphids when scouting soybean fields, but the risk of economic damage in Manitoba is still currently low.

Grasshoppers: Some localized high populations of grasshoppers have been of concern and controlled. In one instance a canola field in the Central region, which had many of its leaves already shed, is reported to have had grasshoppers clipping and skinning pods. As we get to the point where adult grasshoppers predominate, control becomes more difficult and insecticide less effective. A report from the southwest indicates that many fields are progressing well enough that widespread control should not be needed.

Sunflower Insect Update: Lygus bug remains the biggest concern in confection sunflowers, although populations are quite variable, and low in some fields. Overall lygus populations have not been at high levels this year. Other plant bugs in sunflowers continue to create some confusion. Sunflower seed weevils continue to be at levels where they are hard to find in most fields.

Surveys and Forecasts

Monitoring Insects in Sunflowers: Pheromone-baited traps for banded sunflower moth continue to show the moth being present, and in some traps weekly counts continue to climb. Highest cumulative traps counts are Altona (230), Souris (203), and Treherne (201). These traps mainly serve the purpose of letting growers and agronomists know when the moth flight is happening and what relative levels of moths are between regions; we do not have data to allow us to speculate on the potential economics of banded sunflower moth based on these trap counts. No consistent trends in moth levels between different regions in Manitoba are detectable in the data.

You may also see the odd adult moth of the sunflower bud moth when you are scouting sunflowers, as the adults are now emerging. Below are pictures comparing banded sunflower moth and sunflower bud moth adults. Note the difference in the brown patterning on the wings. Both are evening fliers, so you usually only see them during the day if you disturb them while walking through the field. Both also belonging to a family of moths known as Tortricidae, which have square tipped wings, giving them a bell-shape when at rest.

Redbacked cutworm dingy cutworm
Sunflower Bud Moth Banded Sunflower Moth