Manitoba
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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect and Disease Update

July 5, 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

• Apothecia of sclerotinia are abundant in some areas.
• Cereal armyworm larvae are being found in some cereal fields in the East/Central region.
• Late blight and blackleg have been found in some potato fields.

Recent Insect and Plant Pathogen Activity

Canola

Sclerotinia: Sclerotia are producing apothecia in fields that had susceptible crops in 2009, especially in fields that are in cereals in 2010. Petal tests have confirmed the presence of ascospores in the air in and around the canola fields and wheat fields. It is Important to spray fungicides in high risk areas.

We are conducting some trials in grower fields to fine tune a Sclerotinia risk forecasting model. We are collecting 100 flower inflorescences from grower fields with < 20% flowering. Petals from the field will be tested for infection by Sclerotinia. The same site will be sampled again 1-2 weeks later, and finally before harvest the plants in the same spots will be rated for Sclerotinia infection. If some growers want to participate and have their field <20% flowered, please contact Dr. Vikram Bisht, Ph-745-0260; Vikram.bisht@gov.mb.ca

Blackleg: Blackleg symptoms on leaves and stems have been reported in southern Manitoba. We will be surveying grower fields for blackleg as part of prairie-wide survey. If growers would like to participate and let us sample their fields (at near physiological maturity) – please contact us.

Blister beetles in canola: A metallic species of blister beetle known as Nuttall blister beetle (Lytta nuttalli) was noted feeding on canola in southwest Manitoba. They will often feed directly on the flowers. They are often found in distinct patches in a field, and may be more common near caragana. Usually they are only abundant in a very small area of a field, and are not considered a major pest of canola. Control is rarely needed. Because of their metallic colour and their habit of feeding high in the canopy they are highly visible when in canola fields though.

Pulse Crops

Green Cloverworms: Some green cloverworm are being found in dry beans, soybeans, and alfalfa in the central region of Manitoba. So far there have been no populations approaching economic thresholds, but agronomists are starting to notice some of the caterpillars in these crops. Green cloverworm will loop when they walk, so it is easy to mistake them for alfalfa looper. One difference though is that green cloverworm will rapidly wiggle when disturbed. Below is a photo of a green cloverworm larva.

 

Green Cloverworm

Potatoes

Late Blight and Blackleg on Potatoes. Late blight has been confirmed in 3 separate sites; both foliar and stem infections. There were a couple of samples that appeared to have late blight stem symptoms, but closer examination showed that they were blackleg infections.

The late blight and blackleg on potato stems can be differentiated easily by putting the stems in a polythene bag with a moistened (not dripping wet) paper towel and left at room temperature. In a couple of days the late blight infected stem will show white sporulation, but the blackleg infected stem will not. Blackleg also has a unique odor – a “wiff” of the opened polythene bag will attest to that.

Cereals

Armyworms: There have been a few reports of true armyworm (Pseudaletia unipuncta) in cereal crops in the Morris, Winkler and Carman areas. This is something to watch for, particularly when scouting cereal fields, although they will also feed on some broadleaf crops. The photo below shows an armyworm from our oat plot at the University of Manitoba farm in Carman.

This is another insect where the population gets blown in on winds from the south. Cereal armyworm likes to hide under debris on the soil during the day, so if seeing feeding on cereal leaves, look on the soil to see if armyworms may be the cause. Some armyworms are getting about 2.5 cm large already, and some fields have been reported to have populations close to 10/ m2.

Slugs in wheat: Slugs were noted feeding on wheat in about a 35 acre patch in a field near Dauphin. It appears they may have moved in from the ditch area. Slugs do need moisture, so this is something that may be more common in wet years such as this. Slugs are not considered an economical pest of cereals in the Canadian prairies, although occasionally they are noted feeding on the cereals, usually near sources of moisture. Below are pictures of slugs and the type of feeding they will do on cereal crops; photos are courtesy of Lyssia Sirski, Dauphin Coop Agro.

Slugs in wheat Slug feeding in wheat

Crown Rust: Crown rust was reported by a Cargill agronomist in oats in the Morris area.

Fusarium Head Blight: Cereals are heading and the Fusarium head blight risk for the 5th of July is moderate for most of the province. Please see the https://www.gov.mb.ca/agriculture/crops/fhb/index.html for the updates on FHB risk. We are conducting some trials with weather monitoring units in some grower fields with the objective of fine tuning the forecast model and make it more location specific.

 

Surveys and Forecasts

Bertha Armyworm: Highest counts of adults in pheromone baited traps are from the central part of the province. However, cumulative counts still rate as low risk (less than 300 per trap). The table below shows the cumulative counts as of data reported July 5th.

Location of trap

Recent Count

Total count since early-May

Neepawa

142

144

Cartwright

26

53

Dunrea

31

40

Killarney

24

40

Pilot Mound

31

31

Benito

31

31

Holland

23

30

The highest single week count is 142 near Neepawa last week.
The highest cumulative count from Eastern Manitoba is 28 from traps near Altona and Ridgeville.

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 runs from July 6th to 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/