Manitoba Insect and Disease Update: June 10, 2014

 Compiled by:
  • John Gavloski, Entomologist
    Manitoba Agriculture, Food and Rural Development
    Phone: (204) 745-5668
    Fax: (204) 745-5690.
  • Vikram Bisht, Plant Pathologist
    Manitoba Agriculture, Food and Rural Development
    Phone: (204) 745-0260
    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.
 
Summary:
Flea beetles and cutworms continue to be the biggest insect concerns in field crops.
 
Current Insect Scouting Priorities
Flea beetles in canola
Cutworms
Check field edges to assess levels of emerging grasshoppers
 
Flea beetles: Foliar spraying, in addition to the seed treatments, is occurring in many areas. There are some reports of fields having been sprayed 2 or 3 times for flea beetles in the eastern region of Manitoba. And several fields have been reseeded in the Central region because of either heavy flea beetle damage or a combination of flea beetle and cutworm damage. 
 
Cutworm: Dingy and redbacked cutworms seem to be our dominant species. Localized spraying for cutworms in a variety of crops has occurred in many areas of Manitoba. The following may help in your decision making if encountering higher levels of cutworms in a field:
  • How long will they feed: If there are still a lot of cutworms under an inch long, then there is still ample time for higher populations to do economic damage. As a general guideline, once they get over an inch long they will be pupating soon and applying controls may be more expensive then the damage you are preventing.
  • Will crops compensate for some cutworm feeding: Some crops, such as flax and peas, can compensate for some of the feeding by cutworms, while other crops, such as corn, have little ability to compensate for feeding by cutworms. Studies in Manitoba found that the loss of some flax plants at lower densities of redbacked cutworm resulted in an increase in per plant yield of remaining plants (The Canadian Entomologist. 1990. pg 21-28). Peas cut early and at the soil surface were able to regrow or branch from subsurface nodes. Canola has been noted to produce more yield per plant when stands get thinner to at least partially compensate for some plant loss, although I am not aware of this being tested specifically for cutworm feeding. However don't assume that the % stand reduction will equal the % yield loss for all crops.  

 
    Figure 1. Dingy Cutworm                                                     Figure 2. Redbacked cutworm larva and pupae

Note the diagonal markings that look like "V's" or tire tracks down the back of the dingy cutworms, and the 2 dull-red stripes down the back of the redbacked cutworm . 

Forest tent caterpillars are at high levels in some areas of Manitoba. A couple of things to note:
  • These are not armyworms. Some have misidentified them as such.
  • Forest tent caterpillars prefer to feed on broadleaf trees, and although you will see them on the ground they are not a pest of crops. 
  •  By the end of June most of the larvae will likely be turning to pupae, so the feeding will be done for the year. Forest tent caterpillars are an early-season defoliator of trees. When levels are high defoliation may seem severe, but trees while produce more leaves and usually compensate quite well for feeding by forest tent caterpillars.

 
Figure 3. Forest tent caterpillar

Photo courtesy of Kaelyn Martin - Paterson Grain

 

Insect Monitoring Update

Diamondback Moth: It is likely that we had a moderate population of diamondback moth blow into some areas of Manitoba. Some higher counts have been recorded in traps in the Eastern and Northwest regions. However, there have been no reports of larvae yet. So we need to wait and see if anything develops from those populations of moths that are present. Highest trap counts, as of June 11th are: Stead (154), St. Adolphe (138), Teulon (75), Elm Creek (71).

Weekly maps for the monitoring program for diamondback moth can be found at: https://www.gov.mb.ca/agriculture/crops/insects/diamondback-moth-monitoring.html