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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect and Disease Update

August 15, 2011                   

Compiled by: John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives
Phone: (204) 745-5668; Fax: (204) 745-5690
Holly Derksen, Plant Pathologist, Manitoba Agriculture, Food and Rural Initiatives
Phone: (204) 750-4248; Fax: (204) 745-5690

To report observations on insects or plant pathogens that may be of interest or importance to farmers and agronomists in Manitoba, please send messages to the above contact address.

To be placed on an E-mail list so you will be notified immediately when new Manitoba Insect and Disease Updates are posted, please contact John Gavloski at the address or numbers listed above.


Recent Insect and Plant Pathogen Activity


Lygus bugs: Some high levels of Lygus bugs were reported over the past week, mainly in the eastern part of Manitoba.

In some areas a large part of the Lygus population will still be in the juvenile stages. One of the concerns regarding Lygus is whether there will be a sudden movement into later flowering crops, such as sunflowers, if canola nearby is cut or alfalfa is swathed. The juvenile stages can not fly, so a recently cut or swathed crop nearby that contains Lygus bugs does not necessarily mean there will be a big movement of the insects into nearby crops. Part of the risk of this happening depends on the stage of the insects. Just another reason why regular field scouting is so valuable.

Diamondback moth: Levels of diamondback moth continue to be high in some canola fields. High populations were reported last week from fields in the Eastern and Interlake regions of Manitoba, and near Brunkild and Dauphin. Some have been finding that a large part of the population in some fields are in the pupal stage, which is a non-feeding stage.

A reminder that if applying insecticide for any insect in canola, the shortest preharvest intervals are 7 days to swathing or direct-combining. Once a canola crop is within 7 days of swathing, insecticides can not be applied for any insect.

Pulse Crops

Soybean Aphids: There are still some high populations of soybean aphids, although there have been several reports over the past week of soybean aphid populations declining significantly in some fields. We have seen a similar situation in some fields in the Carman area. While collecting aphids off soybean plants for a research project we are involved in, we were dislodging very high levels of lady beetle larvae and hover fly larvae off plants in some fields. The levels of hover fly larvae are the highest I have ever encountered. So when checking soybean fields, consider whether the populations are increasing or decreasing, and the level of natural enemies present.

One of the common species of lady beetle larvae we are seeing is the sevenspotted lady beetle, Coccinella septempunctata. A recent study looking at predation rates by two species of lady beetles on soybean aphids found that for sevenspotted lady beetle third instar larvae could each consume up to 105 aphids per day, adult females could each consume up to 115 soybean aphids per day, and each adult male up to 78 aphids per day when soybean aphids are high. (Environmental Entomology: 2009. 708-714).

larva of lady beetle Larva of hover fly
Figure 1. Larva of Lady Beetle Figure 2. Larva of Hover Fly

General Crop Scouting

Cabbage Butterflies: Many people have been asking about what the white butterflies are that seem to be all over the countryside this year. These are cabbage butterflies (Pieris rapae). The adults will be attracted to many flowering plants, but the larvae feed specifically on cruciferous plants. They will feed on canola, and generally prefer to feed on the leaves. They are not normally considered pests of canola, even though you may find the larvae while scouting canola fields.

Cabbage butterfly
Figure 3. Cabbage Butterfly

Female cabbage butterflies have two black spots on the wings and the males only one spot. So this is a female cabbage butterfly in Figure 3.


Surveys and Forecasts

Grasshopper survey: A reminder that estimates of grasshopper populations for the grasshopper survey are done during August, when the majority of grasshoppers are in the adult stage. MAFRI staff normally do the bulk of the survey, however agronomists and farmers who would also be interested in contributing to the survey are encouraged to do so. See the survey protocol for more details of the survey and where to send data. Estimates of grasshopper levels can be collected during regular farm visits. The grasshopper survey protocol is located at:
Please note that the forms still say 2010 and because of the publication ban I am not able to repost the protocol with the 2011 dates on the form. Use these forms and I'll make the date adjustment when the forms are sent in.

Insect Identification

Quiz Question: What is the insect on the corn cob in this picture?

sap beetle

Answer: This is a species of sap beetle. The scientific name of this species is Glischrochilus quadrisignatus. In total there are 45 known species of sap beetles in Manitoba. The species in the photo can become common in Manitoba in some years, and often people will start noticing them this time of year on ripe fruits or vegetables or on corn cobs. The adult beetles feed on ripe, damaged, and decomposing plant materials. They will bore into many types of ripe or overripe fruit and vegetables. They can also be found on kernels of corn initially injured by other insects or birds, although when populations are high they can be found under the husks of otherwise healthy ears of corn. Attraction to undamaged corn may be provided by the moist, fermenting pollen on the corn silk. They may prevent the natural healing of minor wounds or cracks in fruits and vegetables. Insecticides will not give effective control of sap beetles.