Manitoba Insect Pest Summary For 2001

October 15, 2001

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

Diamondback moth arrived in Manitoba early and in large numbers, causing considerable damage to canola. Bertha armyworm populations increased this year, and control was needed in some canola fields in the southwest. Late in the season, Lygus bug numbers were high in canola in the eastern part of the province, while alfalfa loopers were a problem in canola in the central region.

Armyworms and aphids were the main insects needing control in cereal crops. Aphids also had to be controlled in canary seed and peas. Wheat midge populations were high in a few localized areas, but little control was needed.

Larvae of the variegated fritillary butterfly were clipping the bolls off of flax plants in some fields late in the season, resulting in insecticides being applied to some fields in the central region.

Sunflower beetles had to be controlled both as adults on seedling plants, and later as larvae. Thistle caterpillars had to be controlled in some sunflower fields, and banded sunflower moth larvae were found in the seeds from numerous sunflower fields again this year.

In forage crops, larvae of the alfalfa weevil caused heavy damage to alfalfa in the Killarney area, and Armyworms had to be controlled in some timothy fields.

Forest Tent Caterpillar was a problem on many deciduous trees again this year, and Gray willow leaf beetle caused severe defoliation of willow and poplar in the central region. Mosquitoes and horse flies were a concern to livestock.

canola | cereals | flax | sunflowers | peas | soybeans | canaryseed | forage crops | potatoes | trees and ornamental | livestock


Diamondback moth (Plutella xylostella) arrived in Manitoba early, and in large numbers this year. Some canola fields were being sprayed as early as late May, while plants were still seedlings. Larvae were feeding on the young leaves, causing considerable damage. At least 2 fields had to be reseeded because of severe diamondback moth damage to canola seedlings. Economic thresholds do not exist for diamondback moth feeding on canola in the seedling stage, so nominal thresholds had to be created. A threshold of between 25% and 33% of the plant material eaten or damaged, and larvae still present on the plant was suggested. Large numbers of pupae were showing up in a lot of fields by mid-June. In later stages of canola, larvae were feeding on the buds of canola as the buds were coming up. Spraying for diamondback moth tapered off later in the season, although spraying did continue until early September.

Bertha armyworm (Mamestra configurata) had to be controlled in some fields in the southwest region of the province.

Lygus bug (Lygus sp.) numbers in canola were high in the eastern part of the province late in the season. Many canola fields in the eastern part of the province were sprayed for lygus bugs, with some fields in the Niverville and Steinbach areas having to be sprayed twice.

A field of canola grown for seed in the Starbuck area was sprayed to control alfalfa looper (Autographa californica). Alfalfa loopers were causing heavy defoliation to seedlings in some areas of the field. Later in the season, alfalfa loopers were feeding on the pods and seeds of canola. Several canola fields were sprayed for alfalfa looper in the area near Portage la Prairie, and canola fields were also sprayed for alfalfa looper near St. Jean, Gretna, and Plum Coulee (all in the central region). Insecticides did not provide good control in some instances.

There was some foliar spraying of canola for flea beetle (Phyllotreta sp.) control early in the season. There was also some localized heavy flea beetle pressure on podding canola late in the season.

Thrips damage in canola was reported to be heavy in a field in the Swan River area (in the northwest). Lots of scarring was present on the stems, although little damage was noticed on the pods.

Larvae of the painted lady butterfly (Vanessa cardui) were quite noticeable in some canola fields.

The second flush of armyworms (Pseudaletia unipuncta) had to be controlled in some canola fields in late August. They were observed feeding on the pods of canola.

Variegated cutworms (Peridroma saucia) were also observed feeding on canola pods.



Armyworms (Pseudaletia unipuncta) were being controlled in cereal crops as early as late- June. Some cereal fields also had to be treated with insecticides to control aphids this year. Populations of ladybugs became high in some cereal fields late in the season.

Wheat midge (Sitodiplosis mosellana) populations were patchy, with high populations being reported in just a few localized areas. Some fields in areas near Minnedosa, Neepawa, and just south of Winnipeg had high wheat midge numbers.

Wireworms were an early-season problem in localized areas. A wheat field in the Pilot Mound area had to be reseeded because of wireworm damage.



Larvae of the variegated fritillary butterfly (Euptoieta claudia) became quite noticeable in many flax fields in July. Initially the damage was just defoliation, but later in the season they started clipping the bolls off of plants in some flax fields. Boll clipping was quite substantial in some fields, and at least 7 or 8 fields in the central region of the province were sprayed to control the damage.

Armyworms (Pseudaletia unipuncta) had to be controlled in flax both in early July, and again with the second flush of larvae in late August.

Lygus bug (Lygus sp.) numbers of up to 30 per sweep were reported from some flax fields in late August. It is not known to what extent lygus numbers of this magnitude can damage flax.



Feeding by adults of the sunflower beetle (Zygogramma exclamationis) on seedling plants was substantial this year and control of the adult beetles was needed in some fields. Control of sunflower beetle larvae was necessary later in the summer in some fields as well.

Some control of cutworms was needed early in the season.

A couple of fields of sunflowers in the southwest area of the province and some sunflower fields in the region south of Morden and Winkler were sprayed to control thistle caterpillars (Vanessa cardui).

Banded sunflower moth (Cochylis hospes) larvae were found in the seeds from numerous sunflower fields in Manitoba again this year. Sunflower growers are not familiar with this insect, and processors are trying to encourage growers to spray to prevent insect damage to the seeds. Registered insecticides are needed for this insect in Manitoba.



Aphids had to be controlled with insecticides in many pea fields in the central region.

Some control of cutworms was needed early in the season.


Alfalfa caterpillar (Colias eurytheme) was in high numbers in some soybean fields, particularly in the Carman, Morris, and Beausejour areas. The larvae were feeding on the leaves. Thistle caterpillars (Vanessa cardui) and alfalfa loopers (Autographa californica) were also found feeding on soybeans, although only in small numbers.



Many canaryseed fields were treated with insecticides to control aphids, which were well above the economic threshold in many fields. In some canaryseed fields, white heads were noticeable on plants that had high aphid numbers.


Forage crops

Larvae of the European Skipper (Thymelicus lineola) caused substantial damage to timothy in the Vita area (in the southeast of the province) in mid – June.

Larvae of the alfalfa weevil (Hypera postica) caused heavy damage to alfalfa in the Killarney area. This is the same region where heavy feeding by alfalfa weevil was noticed in 2000. Damage by alfalfa weevil was also noted in the Brandon area.

Control of plant bugs was needed in some fields of seed alfalfa.

Green grass plant bug numbers were high in some timothy fields in the Beausejour area and seemed to be doing substantial damage to the heads. Two-spotted spider mites (Tetranychus urticae) caused damage in some seed alfalfa fields in the Dugald and Arborg areas.

Armyworms (Pseudaletia unipuncta) had to be controlled in Timothy. Feeding on the heads was occurring by the first week in July. Armyworms were also a problem in alfalfa in some areas.

A couple of alfalfa fields in the eastern region of the province had high levels of defoliation from the alfalfa caterpillar (Colias eurytheme).



Variegated cutworms (Peridroma saucia) were observed feeding on potato plants. Some potato fields were sprayed in early-September to control variegated cutworms, although defoliation was only in the 10-15% range. Grower and agronomists obviously needed to be better educated on the economics and harm from applying insecticides at lower levels of damage.

Insects on Trees and Ornamental Plants

Forest Tent Caterpillar (Malacosoma disstria) was a problem on many deciduous trees again this year. Gray willow leaf beetle (Pyrrhalta decora) caused severe defoliation of willow and poplar in the areas around Carman, Winkler, Morden, Kane, Sperling, Homewood, Starbuck, and Sanford. Adult beetles were also reported feeding on apple trees, grape leaves, and some other plants not normally affected. This was likely due to the tremendous numbers in the affected areas this year.

Lily leaf beetle (Lilioceris lilii) was found on lilies near Portage la Prairie. This insect was first found in Manitoba in 1998, and there are worries about this insect spreading.


Insects on Livestock

Mosquito control in livestock was an issue this year, due to the overabundance of rainfall in many regions of the province. Horse flies affecting cattle was also a concern in the eastern region.


Banded Sunflower Moth: There are currently no insecticides registered in Manitoba to control this insect. Some states bordering Canada have several insecticides registered for banded sunflower moth. Getting some of these insecticides registered for banded sunflower moth in western Canada should not be very difficult and is a priority.

Cereal Leaf Beetle (Oulema melanopus) – The Canadian Food Inspection Agency and Manitoba Agriculture and Food continue to monitor for this insect. Cereal leaf beetle has not yet been found in Manitoba.

Nosema Locustae: Requests have been made to Manitoba Agriculture and Food to pursue registration for Nosema locustae for grasshopper control in western Canada. One of the groups interesting in such a registration is organic farmers. In many instances even killing a portion of the grasshopper population is all that is needed. Farmers in Manitoba are seeing farmers in States nearby using such products, and with a proposed harmonization of pesticides between Canada and the United States are wondering why they are being denied tools that are available to nearby farmers.