Manitoba
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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect and Disease Update

July 19, 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

• Armyworms continue to be found in cereal fields, although many are now starting to turn to pupae.
• Root rot, root maggots and blackleg have been concerns in some canola fields.
• Some economical levels of aphids in peas have been detected in later seeded fields. However, many pea fields are too far advanced for control to be economical.

Recent Insect and Plant Pathogen Activity

Cereals

Armyworms: There has been some spraying for armyworms in fields in the Winkler and Rosetown areas. Populations of larvae may be decreasing now in many fields as they are starting to turn to pupae.
So the feeding damage from armyworms will be coming to an end for this generation. We can expect a second generation of larvae, but this likely won’t occur until about mid-August. The pupa stage usually lasts about 18 days, after which adult moths will emerge. These will lay eggs on the lower leaves, and larvae hatch from the eggs in about 2 weeks. A lot of our cereal crops could be too advanced to be good food plants for armyworm larvae by the time the next generation of larvae are present.

The photo below shows the larval and pupal stages of armyworms from our colony kept for the Crop Diagnostic School. On the right in the photo are 3 pupae. The lighter coloured pupa at the bottom-right in the photo had recently transformed into a pupa, and soon darkened. At the top left in the photo is the pre-pupal stage. Although it still looks somewhat like a larva it is not feeding anymore, has shrunk, and is getting ready to turn into a pupa. Note that although it is a more advanced stage than the 2 larvae below it in the photo, it is smaller than these larvae. The small green specks on the ground near the larvae are their feces. You may see a lot of this on the ground in fields that had a lot of armyworms. In a natural situation the larvae would burrow into the soil before turning to pupae.


Armyworm larvae and pupae

Head blight in winter wheat: Most winter wheat crops are now maturing and head blight rating up to 20-30% have been noted.

Canola

Canola Disease Update: There have been a few samples recently of diseased plants from canola-canola rotation. High incidence of root rot is being recorded; some such fields also had high root maggot damage accompanied with blackleg infection of R-rated varieties. Certain areas in Manitoba have very tight rotations, which could contribute to more widespread issues of root damage by insects and diseases.

A survey will be conducted for blackleg in canola. We welcome grower participation by letting us know which fields could be surveyed.

Diamondback moth: Diamondback moth continue to be found in canola fields, but generally at below economical levels. Although they can do some feeding on buds and flowers, as well as leaves, canola is very good at compensating for damage to buds and flowers when soil moisture is good. In most cases it will likely be the later generation feeding on pods that poses the greatest risk this year. So continue monitoring for these and other potential pests in canola.

Thrips: Thrips feeding on canola can cause the pods to curl. Some curled pods and thrips have been noticed on canola in the Altona area.

Sunflowers

The National Sunflower Association of Canada and Manitoba Agriculture, Food and Rural Initiatives are collaborating again to monitor emergence of adults of banded sunflower moth and sunflower moth. Banded sunflower moth is now emerging. Some have also indicated they are noticing lygus bugs on the heads of sunflowers. Sunflowers should be examined for the presence of seed feeding insects. So far there have been no reports of seed weevils, which generally have been in low numbers over the past few years.

Note that if applying insecticides to sunflowers, that pollinators can result in a very significant increase in sunflower yield, even in hybrid varieties. So make sure steps are taken to preserve pollinators and minimize damage to beehives. Spray as late in the day as possible if insecticides are needed, and choose a product that is less harmful to bees. And note that less harmful to bees does not imply less residual action on the pest insects.

Pulse Crops

Aphids in peas: A reminder that the beginning of flowering in field peas is the time to be scouting for aphids. Information on economic thresholds and scouting can be found at: https://www.gov.mb.ca/agriculture/crops/insects/fad14s00.html

Some have been asking about the economics of spraying for aphids in peas once the crop is beyond the early-podding stage. Most of the damage that aphids do to peas is to the pods before they start to fill. If most of the pods have already started to fill, spraying would be too late and would likely not be economical.

There are some later-seeded peas in southwest and Central Manitoba where economical populations are being found.

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) in most areas. However, there was a significant increase in numbers in a trap near Benito last week, placing it in the uncertain risk category. The table below shows the cumulative counts as of data reported July 19th.

Location of trap Recent Count Total Count since early-June
Benito 400 551
Pilot Mound 88 276
Carberry 70 219
Neepawa 21 165
MacGregor 21 107
Hamiota 28 103
The Pas 36 101

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