Agriculture

Manitoba Insect and Disease Update: Week of July 15, 2013

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
 

Insects in Canola: Currently the insect populations of potential insect pests are relatively low and below economic thresholds in most areas, with the exception of grasshopper populations being high around the edges of some fields. Although the eastern part of Manitoba did have some high levels of adults of diamondback moth in the pheromone-baited traps, levels of larvae have not been high. Some larvae can be found but at levels well below economic threshold. In some areas, larvae are starting to turn to pupae, completing the first generation.

Bertha armyworm moth counts are at moderate to high levels in some areas; see table below. 

Lygus bugs can be found in canola, but so far no levels approaching economic threshold have been reported.

 

Insects in Cereal Crops: Currently there are no economic population of insects being reported in cereal crops, aside from some grasshopper control being needed. Most of the grasshopper control has been around field edges so far. We are just starting to see adult grasshoppers now. Based on populations in the Carman area, the twostriped grasshopper (Melanoplus bivittatus) seems to be the most common species of grasshopper this year.

 
    Twostriped grasshopper adult

Aphids are starting to show up in some cereal fields, but so far no populations approaching economic threshold have been noted. Natural enemies can often help keep aphid populations below economic levels.

Surveys and Forecasts

Bertha Armyworm:
 
High counts of adult moths are being noted in the Elm Creek / Sperling area, and also in the area around Roblin. There are also quite a few fields in the "uncertain" risk category. So when scouting canola fields, make sure to look on the ground for larvae of bertha armyworm, and currently you could look on the lower surface of the leaves for the clusters of eggs or young larvae.
 

Egg mass of bertha armyworm
 
Note that the pheromone is attractive to the male moths only, and high trap counts do not mean that the field the trap was in was particularly attractive for the egg laying females, and does not mean that that specific field is at high or moderate risk of bertha armyworms being a concern. Crop stage can make some fields more attractive than others to the females, so populations can vary greatly from field to field, and higher populations in an area may not be in fields that had higher trap counts. The traps are a regional monitoring tool, and what is important is that fields in a region that has higher trap counts be scouted. The table below shows the highest trap counts in the bertha armyworm adult monitoring program.  
 
              Risk of bertha armyworm based on moth capture in pheromone-baited traps
 0-300 = Low risk     300-900= Uncertain risk     900-1,200= Moderate risk  1,200+= High risk
Location Total Count
Elm Creek 1070 M
Zelena (north of Roblin) 969   M
Sperling 967   M
Ridgeville 770   U
Makaroff 758   U
 
A table showing data from the bertha armyworm monitoring program can be viewed on the MAFRI website at:
 
 

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