Manitoba Insect Pest Summary For 2007

November 2007

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 2007 (shown in brackets under each commodity title) are from the Manitoba Crop Insurance Corporations 2007 Variety Market Share Report. The symbol ↑ indicates an increase in acres from 2006, whereas ↓ indicates a decrease in acres from 2006.

Summary

Summary: In cereal crops, wheat midge populations were high in some areas in the western part of the province, resulting in some spraying of insecticides. Wireworms were at high levels in some fields near Teulon. White heads caused by wheat stem maggot were quite noticeable in many fields.

In canola, bertha armyworm populations were high in some areas of the province, resulting in some insecticide applications, however levels were not as high as expected based on trapping of adults earlier in the year. Cutworm populations were high in some areas, resulting in spraying and reseeding of crops. Aster yellows was more noticeable in canola this year than is normal.

Levels of lygus bug (Lygus spp.) were high in many sunflower fields during the flowering period, resulting in control in many fields of confection sunflowers.

Green cloverworm was at noticeable levels in many fields of dry beans and soybeans. Pea aphid levels were high in many fields of field peas.

Alfalfa weevil was a concern in many alfalfa hay and seed fields.

Small Grain Cereals

(Wheat (spring)-2,160,168 acres↓; Wheat (Winter)-450,112↑; Barley-872,517 acres↑; Oats-945,263 acres↑; Rye-47,065 acres↓; Triticale-2,127 acres↑)

Cutworms: There were not many reports of cutworms being problematic in cereal crops this year.

Wireworms: Three fields of wheat near Teulon (I), all of which had been wheat last year, had quite high feeding damage from wireworms. High levels of wireworms in cereals were also reported near Neepawa (SW) and Cypress River (C).

Aphids: Aphid populations got to high levels in some cereal fields, with the majority of reports coming from the southwest. Spraying to control aphids was reported from oats near Medora (SW), and from barley west of Deloraine (SW).

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 Hamiota (SW) and Rivers (SW), and a few later seeded wheat fields in the Swan River Valley (NW) were sprayed for wheat midge. In the southwest, some have commented about significant yield losses because of wheat midge, and there will be a lot of concern about wheat midge in this region for next year.

The following are results to date (October 11) of The Canadian Grain Commission 2007-08 Harvest Survey of Canada western red spring wheat. In the table below the term “factor” refers to any sample showing the presence of wheat midge as a downgrading factor (at any level).

Region	Crop District	# of samples	# of samples with factor	% samples with factor
Southwest	1	99	10	10.1
	2	62	12	19.4
	3	51	12	23.5
Northwest	4	44	5	11.4
	5	61	1	1.6
	6	60	4	6.7
Central	7	80	2	2.5
Central	8	110	3	2.7
Eastern/Interlake	9	33	0	0
	10	14	0	0
	11	7	0	0

Grasshoppers: Populations of grasshoppers were generally below economic levels in 2007, although populations do seem to be increasing. Some fields had the margins treated to manage grasshopper numbers. A wheat field in the Eastern region had insecticide applied to control grasshoppers.

Wheat Stem Maggot (Meromyza americana): White heads caused by wheat stem maggot were quite noticeable in many wheat and barley fields. Some reports were of up to 10% of the heads damaged by wheat stem maggot. Two agronomists reported that the earlier seeded crops seemed to have more wheat stem maggot.

Wheat Curl Mites (Aceria tosichella): Wheat streak mosaic, which is spread primarily by the wheat curl mite, was confirmed in a few fields of winter wheat in the Red River valley and Somerset areas, and in several fields of spring wheat and winter wheat in the southwest. Two spring wheat fields near Boissevain had to be reseeded because of wheat streak mosaic. It is suspected in both instances that volunteer winter wheat in the canola stubble may have provided the bridge for the mites to get to the spring wheat.

Corn

(169,054 acres grain corn↑; 59,655 acres silage corn↑)

Cutworms: A corn field near Elgin (SW) had high levels of damage due to cutworms.

European corn borer (Ostrinia nubilalis): In 2007, 63.9 % of grain corn was seeded to Bt varieties, and 10.8% of silage corn was seeded to Bt varieties. In a survey of 13 corn fields in July and August, very low levels of European corn borer were found. There has not been a significant, widespread outbreak of European corn borer in Manitoba since the mid-1980’s.

Canola And Mustard

(Argentine canola-2,822,394 acres↑; Polish canola-216 acres↓; Mustard-2,872 acres↓)

Flea beetles (Phyllotreta spp.): Flea beetle levels and emergence were such that some foliar spraying was needed, in some cases in addition to the use of an insecticide seed treatment. In many of these instances it was the headlands that were treated.

Cutworms: Cutworm feeding on canola seedlings was heavy in several areas of Manitoba. Canola near Elgin (SW) and Fannystelle (C) was reseeded because of cutworm feeding. A couple of canola fields near Killarney (SW) were treated to control cutworms, and heavy cutworm feeding in canola was also reported in fields near Lauder (SW), Grosse Isle (I) and Oak Bluff (C).

Bertha Armyworm (Mamestra configurata): Although some high populations of larvae of bertha armyworm were found, and adult monitoring suggested high larvae populations, overall the level of control was less than expected. Control of bertha armyworm larvae was reported from canola fields in the Swan River valley (NW), near Inglis (NW), some fields between Boissevain and Deloraine (SW), and near LaRiviere (C). Most of the control that was needed seemed to have occurred from about July 27th through the first week in August.

Pheromone traps for adult bertha armyworm moths were set up at 97 locations in Manitoba. The monitoring period was June 10th to July 28th. The following tables summarize the results:

Number of locations at given risk levels of larval infestation based on cumulative trap catches of moths.

Risk Level	Low (0-300)	Uncertain (300-900)	Moderate (900-1,200)	High (1,00+)
# of locations	34	47	11	5

Locations that had high risk based on catches of adult moths were LaRiviere (C)-1,547, Waskada (SW)–1,465, Pilot Mound (C)-1,464, Bradwardine (SW)-1,379, and Swan Lake (C)-1,362.

The first week in July was the period with the most traps with peak catches.

Summary of weeks with peak catch of adult bertha armyworm moth in pheromone baited traps.

Week	June 17-23	June 24-30	July 1-7	July 18-14
# of traps with peak catch	4	21	33	16

Some observations and concerns of interest include:

In a field in the northwest that had over 1,100 moths in the trap, no larvae could be found. This reinforces that traps are to be interpreted regionally, not on a field-by-field basis.
Instances were reported where diamondback moths were misidentified as bertha armyworm, and grasshopper feeding was mistaken for bertha armyworm feeding.
Some farmers in the northwest were mixing insecticide with fungicide to attempt to kill adults of bertha armyworm. The rationale seemed to be that they were spraying anyway, the insecticide was cheap, so it may be worth it. There were some agronomists promoting this. Such an approach is heavily discouraged. There is no science to show that this would work, it is a step backwards for a canola industry that has tried hard to promote the use of integrated pest management, and it has the potential to cause more insect problems than it solves.

Diamondback moth (Plutella xylostella): Populations of diamondback moth were high in some areas and some control of diamondback moth in canola occurred. Highest populations, and incidents of control were reported from the Eastern, southern Interlake and Southwest regions of the province. Pheromone traps for adult moths were set up at 54 locations in Manitoba. The monitoring period was May 20th to June 30th. Counts were generally low. The highest cumulative counts over a 6 week period was 33 (near Roblin (NW)), while the highest single week count was 20 (near Carberry (SW)) during the week of June 10-16.

Lygus bugs (Lygus spp.): There were no reports of high levels of lygus bugs in canola this year.

Aster Yellows: Incidence of aster yellows, which is vectored by the aster leafhopper, Macrosteles quadrilineatus, was more noticeable this year than most. Because plants with aster yellows remain upright when the weight of healthy canola causes the plants to lean as the pods fill, infected plants stand out and it is easy for farmers and agronomists to overestimate the level of infected plants. Some of the higher claims were that 30-40% of the plants were infected, but these were not substantiated. Some agronomists indicate that farmers are wanting to tank mix an insecticide with other applications to try to spray for the leafhoppers and reduce incidence of the disease. This approached is not advised. Incidence often depends on the time of arrival and distribution of leafhoppers already carrying the phytoplasm, and high incidence of aster yellows in canola are not a common problem.

Flax

(Flax-176,681 acres↓)

Insect populations were low in flax fields in Manitoba in 2007. Three flax fields (near Morris, Darlingford, and Portage la Prairie) were surveyed in June and July to determine insect levels, which were generally low. The highest count of potato aphid (Macrosiphum euphorbiae) during the survey was 30-40 per 10 sweeps.

Sunflowers

(110,501 acres non-oil↓; 65,481 acres oil↑)

Wireworms: There were a few reports of wireworms in sunflower fields in the Central region of the province, however damage was generally not extensive.

Cutworms: There were reports of sunflower fields near Carman (C) and Grosse Isle (I) being sprayed with insecticide to control cutworms.

Sunflower beetle (Zygogramma exclamationis): Sunflower beetle populations were generally below economic threshold, with a few exceptions in the Central region where some fields were sprayed with insecticide. There was some concern that populations well below economic threshold were being sprayed in some fields.

Sunflower Bud Moth (Suleima helianthana): Sunflower bud moth feeding damage was very prevalent in many sunflower fields this year. Although there are no management options once the damage is seen, it causes concern for many growers and agronomists.

Seedhead Insects

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.

Banded Sunflower Moth (Cochylis hospes): Banded sunflower moth populations were noticeable in some fields, and were the main target of some insecticide applications to confection sunflowers in the Central and Eastern Region.

Lygus bugs (Lygus spp.): Lygus bug populations were high in many sunflower fields during flowering, resulting in spraying in many fields of confection sunflowers. 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)

(175,104 acres↓: White pea (navy)-68,522 acres↓, pinto-67,384 acres↑, kidney-13,667 acres↓, black-13,108 acres↓, cranberry-3,474 acres↓, small red-3,055 acres, other dry ebible-5,894 acres)

Green Cloverworm (Hypena scabra): Green cloverworm was noticeable in many fields of dry beans. Some fields in the Portage la Prairie area were sprayed to control green cloverworm.

Lygus bugs (Lygus spp.): The only report of dry beans being treated with insecticide to control lygus bugs was from a field of dry beans near Carberry. There was some seed damage consistent with lygus bug feeding found on white beans from isolated fields in the Winkler and Portage la Prairie areas.

Peas

PEAS (Field) (97,076 acres↑)

Pea aphids (Acyrthosiphon pisum): Levels of pea aphid were high and insecticides applied in several areas of the province. Some of the areas where controls for pea aphids were applied include farms near Headingley (C), Swan Lake (C), Pilot Mound (C), Crystal City (C), Waskada (SW) and Goodlands (SW). Most of the control for pea aphids was applied in early-July.

Soybeans

(213,157 acres↓)

Seedcorn maggot (Delia platura): High levels of damage to soybeans from seedcorn maggot were reported from fields near Elie (C) and Teulon (I). About 80 acres (out of 160) of the soybean field near Elie had to be reseeded because of the damage. In the field near Teulon it was reported that about 10% of the plants were damaged, with about 2% mortality.

Green Cloverworm (Hypena scabra): Green cloverworm was noticeable in some soybean fields in the Eastern and Central regions. Some soybeans in the Dufrost area were sprayed to control green cloverworm.

Soybean Aphid (Aphis glycines): After soybean aphid levels reached economic levels for the first time in Manitoba in 2006, levels of soybean aphid were extremely low in 2007. There were no reports of soybean aphids, and in the 6 soybean fields that were scouted in June and July as part if our MAFRI insect monitoring program no soybean aphids were found.

Fababeans

(7,905 acres↓)

No insect problems were reported from fababeans in 2007.

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 many alfalfa hay and seed fields in the Eastern, Interlake, Central and Southwest regions of the province. Some insecticides were applied as control measures. There was some concern that dimethoate was not killing alfalfa weevil larvae, even when a pH adjustor had been used.

Grasshoppers: Grasshoppers were controlled in some pastures in the Central region.

European Skipper (Thymelicus lineola): European skipper populations were high in many areas this summer. Fields of timothy were treated in the Portage la Prairie area.

Potatoes

(75,080 acres↑; 69,860 acres processing potatoes↑, 5,220 acres table potatoes↓)

Colorado Potato Beetle (Leptinotarsa decemlineata): The population levels of Colorado potato beetles were generally considered to be low to normal in most cases as the neonicotinoid seed treatments seem to be continuing to work well. There was some mention of the length of protection being a little shorter than usual, but this seems to be a common complaint in years where abundant rainfall happens early in the year and seems to reduce that time period of protection. The generation timing of the beetles this year was about as normal as can be with ‘spring’ adults emerging through June and peak populations in late June, early July. Fall adults were observed in early August and some egg-laying did occur.

Potato Flea Beetle (Epitrix cucumeris): As is the usual case, potato flea beetles were locally abundant, typically more so in the Portage la Prairie area than in other regions. Some spraying was done to control populations though there remains debate as to whether this is necessary or not. The literature indicates that for the potato flea beetles to have a significant impact it must be coupled with significant early season defoliation by the Colorado potato beetle. In the absence of that early defoliation, the literature indicates that even dramatic populations of potato flea beetles will not have a significant impact.

Potato leafhopper (Empoasca fabae) and Aster leafhopper (Macrosteles quadrilineatus): In recent years there has been more focus on the potato leafhopper than any other species of leafhopper affecting potatoes. Potato leafhopper was present in 2007 though only in small numbers and no reports of spraying to control this pest were made. Rather the problem in 2007 was the presence of the aster leafhopper which was present in very significant numbers. Approximately 25% of the acres were sprayed at least once in an attempt to control aster leafhoppers.

Sprays to control the aster leafhoppers may provide some benefit, but are typically made in response to visible symptoms already expressed in potatoes. Given that these symptoms occur approximately three weeks after the leafhopper has transmitted the phytoplasma to the potato plant, there may be limited benefit in spraying. The spray will knock down the current population of leafhoppers and prevent transmission for a period of time, but based on observations from carrot sampling for leafhoppers that period of time is about two weeks before the aster leafhoppers have completely re-infested the fields and continue to feed. Multiple sprays, starting much earlier, would be necessary to control purple top and this is not the current approach and is probably not economically feasible in potatoes.

Aphids: Aphid numbers were moderate in potatoes this year.

Sweet Corn, Carrots, Cole Crops, And Other Vegetable Crops

Late summer populations of crucifer and striped flea beetles caused significant damage to cole crops. The early swathing of canola may have moved many of these beetles to cruciferous weeds and vegetables. Control of cabbage looper was necessary on a consistent basis in cole crops this year, as warm September temperatures extended the potential for damage later into the year.

Populations of aster leafhopper remained high for much of the season and were a concern in vegetable crops. Populations of leafhoppers were substantial enough that even when sprays were applied to carrot crops, populations remained sufficiently high that the economic threshold continued to be exceeded. In years past, it has also been observed that sprays would generally give two to three weeks of population suppression before again exceeding the economic threshold. At times this year there wasn’t enough suppression or if there was, the duration was only for a period of one to two weeks at most.

Populations of European corn borer in sweet corn were generally low this year.

A summary of insects on these vegetable crops in Manitoba can be found on the Manitoba Weekly Vegetable Report

Hemp

(4,462 acres for grain↓)

No insect concerns were reported from hemp in 2007.

Insects In Stored Grain

In general, stored product insect discoveries were slightly higher than normal.

Rusty Grain Beetle (Cryptolestes ferrugineus) continues to be one of the more common insects found in stored grain.

There were several interceptions of the lesser grain borer (Rhizopertha dominica) in Manitoba this year. This insect appears in Manitoba occasionally. However, the general position is that this insect is expanding its demographic range and it is just a matter of time before we discover it more frequently.

It is important that producers prepare bins properly before storing grain, and cool grain quickly.