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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect Update

June 24, 2008                   

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

To report observations of insect activity or control that may be of interest or importance to others in Manitoba, please send messages to the above contact addresses.

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Summary

Cutworms continue to be the biggest insect concern but are starting to pupate. Diamondback moth trap counts were low over the pest week.

Recent Insect Concerns and Observations

Cutworms continue to be the biggest insect concern in most areas. However the cutworms are starting to pupate, so the populations of the damaging larval stage are diminishing quickly. So anyone noting what appears to be cutworm feeding is advised to dig and find the cutworms and determine the staging. In most cases they will probably be fully grown and starting to pupate.

High levels of spider mites were reported from a seed alfalfa field in the north Interlake. With leafcutter bees about to go on seed alfalfa fields, the use of insecticides becomes not an option, and estimating the impact of spider mites is always tricky. It was reported that the spider mite population decreased after some recent heavy rains. This is common, and spider mites are usually more of a concern in drier years.

Some questions came in last week regarding European skipper in timothy. This is a small green caterpillar that can role the leaves together and feeds on the leaves. The larvae are present early in the season. The questions last week were regarding thresholds and control. Economic thresholds are established, and are six larvae in a 30 x 30-cm area found in the early, brown-headed stage of the larvae. But as with the cutworms, it may be getting a bit late to be considering control of European skipper.

Sunflower beetle adults are out, but I have not heard any reports of economical populations yet. A reminder that on seedling plants the economic threshold is at least 1 to 2 adults per seedling on average. As the plants develop the threshold would get larger. So far there seems to be just minor feeding that the plants can recover from.

 

Surveys and Forecasts

Diamondback moth:  The increased counts that had occurred in the southeast in early June seem to have stabilized; counts were lower this past week. Although the risk from diamondback moth is not great at this point, agronomists and farmers should pay attention for diamondback moth larvae or feeding damage while scouting canola, particularly in the southeast. Data from the diamondback moth trapping program and an interpretation of the data are available at: https://www.gov.mb.ca/agriculture/crops/insects/db/index.html

Bertha Armyworm: All trap counts reported are very low so far (0, 1, or 2). Bertha armyworm adults are very slow in emerging this year.

Insect Identification Quiz:

 Cutworms

Question: These cutworms were all found in the same field. How many species of cutworms are present in this photo?

Answer: These are all redbacked cutworms. There can be some variation in colour, as is common with many insects and animals in general. Note that they all have the pale stripe down the middle of the body, bordered by darker colouring. On either side of this middle stripe is the “red back” the cutworm is named for, but the shade can vary and will be bordered by dark stripes.

In the field where we found these cutworms last week, there was at least an equal amount of pupae. So the damaging stage is nearly done for this year.