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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect Update

July 6, 2009                   

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.

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


Summary

Alfalfa weevil larvae are at high levels in some areas of Manitoba, with economical populations being reported from the Interlake. High populations of young grasshoppers are also occurring in some areas of Manitoba.

Recent Insect Concerns and Observations

Alfalfa Weevil: Alfalfa weevil are quite numerous in many alfalfa fields, with economical levels being reported over several areas of the Interlake. The larvae are the main damaging stage, and most of the population is currently in the larval stages. Alfalfa fields should be scouted to determine the presence and abundance of alfalfa weevils. Note that for hay crops, if alfalfa has reached the bud or early bloom stage, immediate cutting will kill many alfalfa weevil larvae. The following image shows some alfalfa weevil larvae. They may be light yellow when they hatch, but will become a pale green colour and have a white stripe down the back.

 
Alfalfa Weevil Larva  

The Manitoba Weekly Forage Seed Report has some current information on insects that are being monitored in forage seed crops, including alfalfa weevil. It is available at:
https://www.gov.mb.ca/agriculture/crops/mfsr/index.html

Grasshoppers: High populations of young grasshoppers continue to be noticed in and around some fields. Most of the reports of higher populations so far have been from the southwest and central regions of Manitoba. Now is a good time to be checking areas that can potentially be grasshopper hotspots. If populations are such that it appears control will be needed, grasshoppers are much easier to manage when they are young and concentrated near where they emerged.

 

Surveys and Forecasts

Diamondback Moth Forecasting: Counts of diamondback moth continue to be generally low. However, counts have increased in the eastern part of Manitoba, as well as from a couple of traps in the Northwest. Agronomists and farmers in these areas should make sure to look for diamondback moth larvae when scouting canola; either through sweep net samples if you are taking them, or tapping plants and counting larvae. If larvae appear abundant, tapping plants and counting the number of larvae on average in a square foot of plants will determine if control may be economical. Data and interpretations of adult trap counts can be viewed at:
https://www.gov.mb.ca/agriculture/crops/insects/db/index.html

Note that we are getting to the point in the season where sampling for larvae of diamondback moth is easy and more meaningful data than adult counts. So traps for diamondback moth can be removed the next time traps are checked. If you also have traps placed for bertha armyworm, do not remove these, they should be kept up until the end of July. It is just the diamondback moth traps that can be removed at this time.

Bertha Armyworm Forecasting: So far, counts from the traps for bertha armyworm are also very low. Highest counts so far are from traps near Miniota (74), Elkhorn (53), and Belmont (40). These still rate as low risk (less than 300), although we still may not be far into emergence. Data can be viewed at:
https://www.gov.mb.ca/agriculture/crops/insects/bertha/index.html

Wheat Midge Emergence: The Canadian Wheat Board produces maps that predict based on growing degree days when wheat midge emergence should be starting and peaking. Maps will be updated daily until the end of July. So far the maps show that enough degree days have only been accumulated in small areas of southern Manitoba for the emergence of wheat midge to begin, however percent emergence would still be low. Maps can be viewed at: http://www.cwb.ca/public/en/farmers/weather/midge/