Manitoba Insect Pest Summary For 2006

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

Abbreviations used: The following abbreviations will be used in this document to indicate the following agricultural regions in Manitoba; NW=Northwest, SW=Southwest, C=Central, E=Eastern, I=Interlake.

Estimated acres: Estimated acres grown in Manitoba in 2006 (shown in brackets under each commodity title) are from the Manitoba Crop Insurance Corporations 2006 Variety Market Share Report.

Summary

In cereal crops, aphid populations reached high levels in some fields, making control economical. Wheat midge (Sitodiplosis mosellana) populations were high in some areas, resulting in some spraying of insecticides.

Bertha armyworm (Mamestra configurata) populations were quite high in some areas of the province, resulting in substantial damage in some canola fields and the use of insecticides for control. Diamondback moth (Plutella xylostella) populations reached damaging levels in the Southern Interlake region and the area north of Ste. Rose. Levels of lygus bug (Lygus spp.) were high in sunflowers during the flowering period, resulting in substantial control in confection sunflowers. High levels of potato aphids (Macrosiphum euphorbiae) occurred on flax in the Central and Interlake regions.

Soybean aphid (Aphis glycines) reached economic levels for the first time ever in Manitoba. High populations occurred on soybeans in the Eastern, Interlake and Central area of the province. Spider mites were a concern on soybeans in the Eastern part of the province late in the season. Populations of pea aphid (Acyrthosiphon pisum) reached high levels in some fields of field peas in the western part of the province, resulting in some insecticide applications.

Small Grain Cereals

(Wheat (spring)-2,834,320 acres; Wheat (Winter)-302,790; Barley-678,469 acres; Oats-771,265 acres; Rye-74,835 acres; Triticale-1,848 acres)

Cutworms: There were not many reports of cutworms being problematic in cereal crops this year. Control was necessary in a fall rye field near Wellwood (SW), and at least half the field had to be reseeded because of cutworm damage.

Wireworms: Some wheat fields in the Gilbert Plains (NW) area had quite noticeable feeding damage from wireworms, and one of these fields was reseeded because of the wireworm damage.

Thrips: Thrips were quite abundant and their feeding was quite noticeable in many cereal fields early in the season. I am not aware of any insecticide being applied to cereals to control thrips, however.

Aphids: Aphid populations got to high levels in many cereal fields, and some spraying to control aphids was done. In some instances insecticides other than those registered for aphids in cereals were applied because fungicides were already being applied to the crop and it was desired to tank mix an insecticide with the fungicide.

Wheat midge (Sitodiplosis mosellana): High levels of wheat midge were present in some wheat fields, and some insecticides were applied. Spraying for wheat midge is known to have occurred near Pilot Mound (C) and Rivers (SW).

Grasshoppers: Populations of grasshoppers were generally below economic levels in 2006. One wheat field Northwest of Morris (C) was reported to have a high population of grasshoppers early in the season, and was sprayed to control them.

Wheat Curl Mites (Aceria tosichella): Wheat streak mosaic, which is spread primarily by the wheat curl mite, was confirmed in a few fields in the southwest and Central regions of the province. Wheat streak mosaic began to be noticed on volunteer cereals in early May. A field of winter wheat west of Somerset (C) was reseeded to canola because of wheat streak mosaic virus.

Corn

(135,150 acres grain corn; 52,779 acres silage corn)

Seedcorn maggot (Delia platura): Seedcorn maggot was noticed in higher levels in corn fields in the Shilo (SW) area.

European corn borer (Ostrinia nubilalis): In 2006, 56.5 % of grain corn was seeded to Bt varieties, and 10.6% of silage corn was seeded to Bt varieties. In a survey of 17 corn fields in July and August, very low levels of European corn borer were found.

Canola And Mustard

(Argentine canola-2,198,971 acres; Polish canola-884 acres; Mustard-3,663 acres)

Flea beetles (Phyllotreta spp.): Flea beetle feeding was generally low enough to be non-economical, however there was some spraying for flea beetles in the Dauphin (NW) and Grandview (NW) areas.

Cutworms: The only cutworm damage in canola that was reported was from a field southeast of Neepawa (SW).

Bertha Armyworm (Mamestra configurata): Bertha armyworm populations were high and insecticides applied to many canola fields in the Northwest area of the province. The heaviest populations and most spraying seemed to be in the Swan River area and north of Minnedosa, with some control also needed in the Roblin area and south of Dauphin. One particular field north of Minnedosa had areas with populations as high as 20 larvae per plant, and most of the yield from the field was lost. There are some reports of fields being sprayed twice for bertha armyworm in the Swan River area. Bertha armyworm could be easily found in many fields in the Brandon area, but at levels below the economic threshold of 25 -30 / meter square being used this year (based on the value of canola and control costs). There were some reports of spraying for bertha armyworm in the Notre Dame de Lourdes (C) and Homewood (C) areas, however, so the higher populations were located much further east in Manitoba in 2006 then they were in 2005. Close attention needs to be given to monitoring for the adult moths in June and July of 2007 to determine if and how widespread high populations are expected in 2007. The traps once again predicted fairly closely the general regions where higher populations could be expected. An interesting observation from one agronomist was that larvae seemed to be more advanced in any of the fields where the stubble had been burned.

Diamondback moth (Plutella xylostella): High populations and some spraying for diamondback moth occurred in the southern Interlake and the area north of Ste. Rose (NW).

Other Lepidoptera: Although not really a pest of canola, high level of zebra caterpillars, Melanchra picta, was noted in localized areas of some fields. These were particularly numerous in the Eastern and Central areas of the province. Two canola fields (near Rosenort and Domain) were sprayed for zebra caterpillar late in the season.

Lygus bugs (Lygus spp.): Some canola in the Beausejour (E) area was sprayed to control lygus bugs.

Flax

(Flax-343,796 acres)

Potato aphid (Macrosiphum euphorbiae): Populations of potato aphid on flax became quite high in some areas late in the season, making decisions on the economics of control quite difficult. In some of the fields, significant numbers of aphids were found on the flax once the crop was past the green boll stage. Many flax fields around and south of Pilot Mound (C) had high numbers of potato aphids late in the season. There was also some spraying for aphids in flax in the southern Interlake in early July.

Lygus bugs (Lygus spp.): A field of flax west of Beausejour (E) was sprayed in late July to control lygus bugs (about 40-50 / 10 sweeps were being found). No insecticides are registered for lygus bugs in flax, and whether controlling lygus bug populations such as these in flax is economical is still uncertain; the one study that has been published found these numbers of lygus bugs in flax had no economical effect under good growing conditions (Wise and Lamb 2000). More research on lygus bugs in flax is needed.

Sunflowers

(150,825 acres non-oil; 41,284 acres oil)

Wireworms: High numbers of seedlings were reported to show some wireworm damage in some fields in the Morden (C) and Plum Coulee (C) areas in late May.

Sunflower beetle (Zygogramma exclamationis): Some high populations and spraying for sunflower beetles occurred in the Eastern and Central areas of Manitoba. In some instances it was the adults that were being controlled in early June, while in other instances it was mainly the larvae being targeted in July.

Seedhead Insects

Banded Sunflower Moth (Cochylis hospes) and red sunflower seed weevil (Smicronyx fulvus): Populations of seed weevils were very low again this year, and usually hard to find when scouting for insects on sunflower heads. Although banded sunflower moth populations were noticeable in some fields, I am not aware of any fields where high populations were reported.

Lygus bugs (Lygus spp.): Lygus bug populations were high in many sunflower fields during flowering, resulting in spraying in many fields of confection sunflowers. Some fields of confection sunflowers were sprayed twice to control lygus bugs. No insecticides are registered for lygus bugs on sunflowers in Canada. Research on insecticides and management strategies for lygus bugs in confection sunflowers is needed.

Beans (Dry Edible)

(178,475 acres: White pea (navy)-81,132 acres, pinto-50,849 acres, black-20,720 acres, kidney-14,197 acres, cranberry-4,801 acres, red Mexican-930 acres, other dry ebible-5,846 acres)

Very few insect problems were reported from fields of dry edible beans in 2006. Populations of potato leafhopper (Empoasca fabae) became noticeable in some fields of dry edible beans around early-July, however I am not aware of any economical populations or insecticides being applied to dry edible beans in 2006.

Peas (Field)

(85,070 acres)

Pea aphids (Acyrthosiphon pisum): A few fields of peas in the Southwest part of the province were sprayed for pea aphids in early July.

Soybeans

(363,788 acres)

Soybean Aphid (Aphis glycines): Soybean aphid numbers became quite noticeable in some fields about mid-July and by late-July several soybean fields in the Eastern and Central part of the province had been sprayed to control soybean aphids. Populations continued to build and more fields surpassed the economic threshold (250 aphids per plant and the population still increasing) and had controls applied in early August. Populations of soybean aphid got quite large in some soybean fields in the Interlake region of Manitoba as well. Heavy soybean aphid populations were reported as far west as Cypress River where a nearby field was reported to have a population of about 1,000 aphids per plant. Crop scouts within a region often reported great variability in levels of soybean aphids: one scouting report indicated finding 250 – 1200 aphids per plant in 14 out of 15 soybean fields inspected west of Lac Du Bonnet (with one field not being too heavily infested yet) while on the same day 4 fields east of Stonewall were inspected and virtually no sign of aphids was found. This is the first year that soybean aphids have reached economic levels in Manitoba.

Spider mites: Spider mites and their feeding damage became noticeable in some soybean fields in the eastern part of the province in mid-August. In some of these fields the damage was very distinctively worse along field edges. Some of these fields were sprayed to control the spider mites.

Fababeans

(8,533 acres) No insect problems were reported from fababeans in 2006

Forages and Forage Seed

Plant Bugs: Insecticide were applied in many alfalfa seed fields to control lygus bugs (lygus spp.) and alfalfa plant bugs (Adelphocoris lineolatus).

Alfalfa Weevil (Hypera postica): Alfalfa weevil was a concern in several alfalfa hay and seed fields in the Eastern, Interlake and Central regions of the province. Some hay fields were cut early, and some insecticides were applied as control measures.

Aphids: High populations of aphids were reported from some alfalfa fields in the Interlake and near Pilot Mound (C), with insecticides being applied to a couple of these fields to control the aphids.

Potatoes

(71,495 acres; 64,431 acres processing potatoes, 7,064 acres table potatoes)

Colorado Potato Beetle (Leptinotarsa decemlineata): It appeared numbers of Colorado potato beetle were up this year compared to lower than usual numbers in the very wet years of 2004-2005. CPB does not do particularly well in cool, wet conditions but does thrive in the type of year we had in 2006. CPB adults had emerged and commenced egg laying in early June, with hatch occurring between mid June and early July. By late July some CPB were observed in fields treated with seed-piece Admire, so foliar treatments were applied. Re-entry of CPB adults to some potato fields was observed in mid August prompting applications to field edges or spot treatments. To a small degree, growers were caught off guard by both the numbers and the speed with which they progressed through the juvenile stages. Another reason for more CPB this year may be because of a substantial decrease in the acreage treated with seed-piece Admire. Some use of older chemistries did not provide control due to resistance. In many cases foliar Admire or Assail was required for control.

Potato leafhopper (Empoasca fabae): There were several reports of potato leafhoppers in processing potato fields. This is a bit unusual in certain respects. Typically when potato leafhoppers migrate into Manitoba we have ample warning from first alfalfa fields and then bean fields that tend to be congregated first. This year we had no such early warning indicators and the reports of leafhoppers were quite widespread to the west of the Portage la Prairie area. Each year, even in what could be considered a non-outbreak year we have fields that are sprayed due to exceeding economic thresholds and it looks like this year it was just a bit more widespread than usual.

Potato Flea Beetle (Epitrix cucumeris): Feeding injury from potato flea beetle was observed by mid June but levels were generally below the economic threshold in most areas of Manitoba. The economic threshold of 10% foliage loss was exceeded in some fields in the Portage area and fields were sprayed in late July.

Aphids: Aphids were detected in potatoes by June 21 and reached very high levels by early August. Although generally less of a concern in table potato production, aphid numbers were high enough this year to cause aphid holes, areas were plants collapse due to high levels of feeding by aphids. Buckthorn aphids, (Aphis nasturtii) and potato aphids (Macrosiphum euphorbiae) were the most abundant specimens collected. Green peach aphids were observed by mid-July and soybean aphids (which will probe but not colonize potato plants) were observed in early August. Seed growers treated aphids in a number of ways. Some fields had advanced quickly with tubers reaching desired size by early August so fields were desiccated. Seed growers tended to use the insecticide Fulfill, which is targeted specifically at aphids. Commercial fields often were treated with a broad spectrum insecticide to also control flea beetles and/or potato leafhoppers.

European corn borer (Ostrinia nubilalis): In 2006, the European corn borer was not abundant in potatoes in Manitoba.

Hemp

(30,630 acres for grain)

High populations of lygus bugs were reported from a hemp field near Darlingford (C), but I am not aware of any insecticide use in hemp.