Manitoba
Printer Friendly

Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect and Disease Update

July 12, 2010                   

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

• Blackleg and root maggots are being found in some canola fields.
• Armyworm larvae are being found in some cereal fields in the South-Central region.

Recent Insect and Plant Pathogen Activity

Canola

Blackleg on canola: Blackleg is showing up on leaves of canola in some fields. Currently it is mainly a problem in fields that are canola on canola.

Root maggots in canola: More canola fields with damage by root maggots are showing up. A field south of Miami was reported to have some plants falling over and roots pinched off, which can happen when heavier feeding by root maggots occurs. This particular field, like some of the other instances where heavy root maggot feeding has occurred this year, was canola last year as well as this year.

Pulse Crops

Green Cloverworms: Some green cloverworms continue to be found in dry beans and alfalfa in the central region of Manitoba. So far only minor feeding has been noticed, so this is just something to monitor but currently not an economic threat. Refer to last weeks update for a picture of a green cloverworm.

Aphids in peas: A reminder that the beginning of flowering in field peas is the time to be scouting for aphids. Although some are reporting finding aphids in peas, in most instances they are below the economic threshold of 9 to 12 aphids per sweep (90-120 aphids if doing a set of 10 sweeps) or an average of 2-3 aphids per 20 cm (8 inches) of plant tip. We are finding quite a few pea aphids in some of the alfalfa in the Carman area, a crop for which the tolerance to aphids is very high. If forage alfalfa has recently been cut near a field of peas that are still in the flowering or very early podding stages, make sure to have a look for pea aphids in the pea crop.

Cereals

Armyworms: Armyworms (Pseudaletia unipuncta) are still being found in many fields of cereal crops, mainly in the south-Central area of Manitoba. Highest populations seem to be in the Winkler area, where there has been controls applied to a few fields. Larvae in some fields are getting into their final growth stages, and some may be starting to pupate. In our colony of armyworms collected from local fields for the Crop Diagnostic School, some have started to pupate over the weekend. Stage of larvae is something to consider when determining the potential economic impact of an armyworm population. If most larvae are greater than about 2.5 cm, they will be finishing feeding and pupating soon, so control in these situations is generally not recommended. In most instances agronomists are noticing larvae and monitoring the situation but not seeing damage to plants or populations high enough to justify insecticide use. However there have been some higher populations found and in some fields larvae are still not in the final growth stages

Figure 1 below shows armyworm larvae, and Figure 2 shows an armyworm pupa. Note in figure 1 the variation in colour, and the habit of curling up when the larvae are disturbed.

Figure 1      Army worm Larvae Figure 2      Armyworm Pupa

 

Surveys and Forecasts

Bertha Armyworm: Cumulative counts of trapped moths of bertha armyworm still rate as low risk of larvae being an economical concern (less than 300 moths in total per trap). The table below shows the cumulative counts as of data reported July 12th.

Location of trap

Recent Count

Total count since early-June

Benito

120

151

Neepawa

142

144

Hamiota

20

75

Dunrea

30

70

Mecconel

15

67

The Pas

58

65

Cartwright

6

59

The following link provides updated trap counts, and information on how to interpret trap counts.
https://www.gov.mb.ca/agriculture/crops/insects/bertha/index.html

Crop Scouting Educational Opportunities

Crop Diagnostic School: A reminder that the Crop Diagnostic School continues this week (until July 16th) at the University of Manitoba Farm in Carman, MB.

Please remember to bring any samples of insects, plant pathogens or weeds you would like us to identify, and come with topics you would like to discuss.

More information on the Crop Diagnostic School can be found at: https://www.gov.mb.ca/agriculture/crops/cdschool/