Manitoba Insect Pest Summary For 2004

November 2, 2004

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.

Summary

The spring and summer of 2004 were very cool and wet in Manitoba, and as a result many insects were well below normal in their rate of development and damaged crops later in the season than is normal. Flea beetles caused widespread damage in canola, and aphids were a concern in peas, cereals and canaryseed in many areas. Cutworms were a concern in many crops. Grasshoppers were not as damaging as has initially been expected. The weather was not favorable for grasshopper development, and natural enemies of grasshoppers were also quite abundant in some areas.

Wheat, Barley, Oats

Cutworms: Cutworms were at levels capable of causing economic damage in a few fields of small grain cereals. What was unusual was how long into the summer the problem lasted this year. Control of cutworms began about mid-May, and there was a field of barley near Teulon (I) that was treated with insecticide to control cutworms as late as July 13th. The field near Teulon was reported to have populations as high as 9-10 / m2, and was noticed after a high population of gulls was spotted in the field.

Wireworms: Wireworm damage was reported from fields near Melita (SW) and in the Gladstone-Plumas area (C).

Grasshoppers: Aside from a report of some barley just north of Plumas (C) being sprayed to control grasshoppers in late July, there were no reports of grasshoppers causing economic damage or being controlled with insecticides in small grain cereals this year.

Wheat midge (Sitodiplosis mosellana): Most of the higher populations of wheat midge were reported from the Southwest. A few wheat fields in the Rapid City (SW) area were sprayed to control wheat midge around July 24th. Midge levels in these fields were reported to be on average about 1 midge per every 1-3 plants. A wheat field from the Waskada (SW) area was reported to have wheat midge levels about 2-3 midge per plant, although in this case the wheat was too far advanced for the wheat midge to be of economical concern.

Aphids: Aphids were a concern in many small grain cereal fields. Application of insecticides to control aphids in small grain cereals was reported from near Portage la Prairie (C), Brunkild (C), Morris (C), and Aubigny (E). Most of these fields were sprayed in the first 3 weeks of August. One of the aerial applicators who had sprayed a few oat fields for aphids noticed that there were more aphids in the oat fields that had earlier been sprayed with the fungicide Tilt for disease control; these fields were staying greener longer. Aside from fields staying green longer, another possible explanation for the increased aphid populations following fungicide applications could be that beneficial fungi that affect aphids could have been killed by the fungicides, as has been found to happen with use of some fungicides (Lagnaoui & Radcliffe 1998, Nanne & Radcliffe 1971, Wilding 1982).

True armyworm (Pseudaletia unipuncta): The population of true armyworm larvae started to get noticeable about mid-July in the Morden-Winkler area (C), and by late July at least 1 field in the area was reported to have a population above the suggested economic threshold of 10/m2. However, I am not aware of any insecticide being applied to control true armyworm.

Canola

Flea beetles (Phyllotreta spp.): For some of the early seeded canola, the insecticide portion of the seed treatments broke down to levels where they were no longer controlling flea beetles while the plants were still quite susceptible to flea beetle feeding. This happened even for seed treatments with higher rates of insecticide. Early season growth of canola was slow in many areas, so the canola took a long time to reach stages that are more tolerant to feeding by flea beetles.

Foliar spraying to control flea beetles was common in many areas again this year. Areas where foliar insecticides were applied to control flea beetles in canola fields include Swan River (NW), Hamiota (SW), Tilston (SW), Carberry (SW), Neepawa (SW), Gladstone (C), Portage la Prairie (C), Notre Dame (C), Starbuck (C), Elm Creek (C), Carman (C), Miami (C), Homewood (C), Sperling (C), Roland (C), Pilot Mound (C), Morris (C), Altona (E), and Riverton (I). Some fields in the Southwest were sprayed 2-3 times to control flea beetles.

Some reseeding of canola because of damage by flea beetles was reported from the Northwest and Southwest, and some fields in the Altona (C), and St. Pierre (E) areas.

The high flea beetle populations persisted well into July in some areas. In the second week of July, concern was raised by an agronomist in the Gilbert Plains area that flea beetles were feeding on the buds of canola, and whether this will result in economic damage or will the plants compensate for this feeding on the buds the way it does for lygus bug feeding.

Cutworms: Cutworms populations were reported to be quite high in some canola fields in the Arborg/Riverton area of the Interlake, with some of these fields being treated with insecticides in late-June. About 1,000 acres of canola in the Hamiota area was also treated with insecticide to control cutworms.

Bertha Armyworm (Mamestra configurata): Adults of bertha armyworms were once again monitored with pheromone-baited traps. Fifty traps were monitored, and counts showed a low risk of larval infestation (0-300 over the monitoring period) in 46 of the 50 traps, and an uncertain risk (300-900 moths) in 2 traps in the southwest and 2 traps in the northwest. There were no reports of bertha armyworm larvae being at or near economic levels in any canola fields. A map of the trap counts for 2004 is available on request.

What is very interesting about the trap counts for bertha armyworm this year is how late in the season the peak counts occurred. In most areas peak counts of the adult moths in the traps occurred any time between July 12th and July 23rd. However, for some of the traps in the northwest peak trap counts were even later. For all 3 traps in the Swan River district, peak catch of adult bertha armyworm was during the week of August 2 to August 6th, which was the last week these traps were up and later than the originally planned period for the traps to be up.

Diamondback moth (Plutella xylostella): Diamondback moth adults were once again monitored with pheromone-baited traps. Eighty-four traps were monitored across Manitoba. Counts were low throughout the trapping period in May and June. Some traps were left up longer than the initial 6 week trapping period, and started to catch some higher numbers of diamondback moth during the week of July 19-23. However, there were no reports of diamondback moth being of economic concern in any canola fields in Manitoba in 2004.

Grasshoppers: There were concerns in some areas over grasshoppers feeding on canola early in the season. A canola field (which was pasture the previous year) near Sidney (C) was sprayed to control grasshopper nymphs in early June. There were also some reports of grasshopper damage to canola in the southwest in June.

Blister Beetles (Epicauta spp.): Blister beetles were quite noticeable in many canola fields this year, although it was mainly Epicauta species that were present, and not the Nuttall blister beetle (Lytta nuttalli) which is the more common species of blister beetle in canola in many years. The black blister beetle (Epicauta pensylvanica) was quite noticeable in some fields. Control was not recommended because of the minimal feeding damage the blister beetles were doing, and because larvae of Epicauta species feed on grasshopper eggs (Horsfall, 1941). A canola plot near Elm Creek was treated with insecticide to control blister beetles.

Flax

Grasshoppers and potato aphids were the main insect pests in flax.

Grasshoppers: A field of flax in the Miniota area (SW) was sprayed to control grasshoppers in late June. Some fields of flax in the Dauphin area (NW) were treated to control grasshoppers in late July.

Potato aphid (Macrosiphum euphorbiae): Fields of flax were treated to control aphids near Lowe Farm (C) and Aubigny (E).

Sunflowers

Cutworms and Wireworms: There were only a couple of reports of cutworms and wireworms being of concern in sunflowers in 2004. A sunflower field in the Grosse Isle (I) area was sprayed with insecticide to control cutworms. Wireworm damage was reported from a sunflower field near MacGregor (C).

Sunflower beetle (Zygogramma exclamationis): Economically significant populations of sunflower beetle were present in some fields in the eastern and central part of Manitoba. Insecticides were applied to control sunflower beetles in sunflower fields near Treherne, Lowe Farm, Horndean, and Altona in the Central region; and Dugald in the Eastern region. These fields were sprayed during the last week in July and first week in August.

Grasshoppers: There was a limited amount of grasshopper control around the edges of sunflower fields. A couple of sunflower fields in the Beausejour (E) area had insecticide treated bait spread around the field edge to control grasshoppers.

Sunflower Midge (Contarinia schulzi): There were a few reports of sunflower midge from the Roland and Altona areas, but no major damage. It seemed to be concentrated in the low lying areas.

Sunflower Bud Moth (Suleima helianthana): Sunflower bud moth was reported from sunflower fields across Manitoba again this year. Although the literature suggests that this pest is not economically significant, some feel the damage they cause is getting close to being an economic problem.

Seedhead Insects

Banded Sunflower Moth (Cochylis hospes) and red sunflower seed weevil (Smicronyx fulvus): There were no reports of sunflower seed weevils being seen at or even near economic threshold levels in 2004. A couple of sunflower fields in the Holland/Treherne (C) area had the edges sprayed to control banded sunflower moth. Lygus bugs (Lygus spp.) were noticed in high numbers on sunflowers in some areas.

Forages and Forage Seed

Plant Bugs: Alfalfa growth and bloom was about 2 weeks later than normal this year, and as a result scouting and insecticide applications to control plant bugs was later than normal. The use of dimethoate was down, and in crop treatments (after the release of leafcutter bees) were up due to the late bloom.

Grasshoppers: Grasshoppers were sprayed on some pastures in the central region in early August.

European Skipper (Thymelicus lineola): There were more reports of damage by European skipper on timothy than normal this year. There was some spraying to control European skipper in timothy in the Fisher Branch and Beausejour districts.

Dry Beans

Cutworms: Cutworms were a problem in a bean field in the Portage la Prairie area. What was unusual was how long into the season the cutworms continued to be a problem. The field was sprayed July 2nd, and a week later there was still evidence of cutworm feeding.

Wireworms and Seedcorn Maggot: Considerable wireworm feeding was noticed in a couple of bean fields in the Boissevain area, while damage from seedcorn maggots was noticeable in a bean field in the Altona area.

Potato Leafhopper (Empoasca fabae): Potato leafhoppers were not an economical concern in dry beans in Manitoba in 2004.

Grasshoppers: Although grasshopper populations were high along many field edges early in the season, there were only a couple reports of control needed in or around bean fields. A field of beans southwest of Portage la Prairie (C) was sprayed to control grasshoppers in mid-June, while the edge of a dry bean field near Elma (E) was sprayed to control grasshoppers in late July.

Peas

Cutworms: There was some insecticide applied for cutworm control in peas in the Hamiota area in early June.

Pea aphids (Acyrthosiphon pisum): Populations of pea aphid on peas were generally quite high for the second straight year. Insecticide applications to control pea aphids began in late July (around July 20th) and continued through the first week in August. Last year aphid control in peas began in the first week in July, about 2 weeks earlier than in 2004. Pea fields are known to have been sprayed to control aphids this year in the Swan River Valley in the northwest, in the Boissevain area in the Southwest, near Neepawa, Pilot Mound and Morris in the central region, and in the Arborg area in the Interlake.

Soybeans

Grasshopper populations early in the growing season were the main insect concern in soybeans this year.

Grasshoppers: Grasshoppers had to be controlled in some soybean fields early in the season in the Morris, Portage and Treherne districts (C).

Soybean Aphid (Aphis glycines): There were no reports of soybean aphids in Manitoba in 2004.

Canaryseed

Aphids: Aphids were once again a concern for many growing canaryseed. Fields of canaryseed were sprayed with insecticides to control aphids near Boissevain (SW), Neepawa (SW), Starbuck (C), Morris (C), Altona (C) and Beausejour (E). Most of this spraying was in the last week of July and the first 2 weeks of August. In contrast, in 2003 most of the reports of aphid control in canaryseed were between July 1st and July 15th.

Literature Cited

Horsfall, W.R. 1941. Biology of the black blister beetle (Coleoptera: Meloidae). Ann. Entomol. Soc. Am. 34: 114-126.

Lagnaoui, Abdelaziz and Edward B. Radcliffe. 1998. Potato fungicides interfere with entomopathogenic fungi impacting population dynamics of green peach aphid. Amer. J. Potato Res. 75: 19-25.

Nanne, Henry W., and Edward B. Radcliffe. 1971. Green peach aphid populations on potatoes enhanced by fungicides. J. Econ. Entomol. 64: 1569-1570.

Wilding, N. 1982. The effect of fungicides on field populations of Aphis fabae and on the infection of the aphids by Entomophthoraceae. Ann. appl. Biol. 100: 221-228.