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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect and Disease Update

July 26, 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

• Diamondback moths are being controlled in some canola fields in eastern Manitoba.
• Soybean aphids have been found in southern Manitoba, but only in small amounts.
• Lygus bug levels should be checked in fields of confection sunflowers.

Recent Insect and Plant Pathogen Activity

Canola

Diamondback moth: Insecticides have been applied to some fields in eastern Manitoba because of high diamondback moth levels. Fields near Winkler, Morris, Altona, and Rosenort have been treated.

Diamondback moth larvae will feed on canola buds and flowers, as well as leaves. However, canola is very good at compensating for damage to buds and flowers when soil moisture is good.

 

Diamondback moth pupa and larva

A reminder that if spraying canola fields that still may have flowers, to spray as late in the day as possible, or very early in the morning if this is not possible. And choose an insecticide that will cause less harm to honey bees. Even if there are no hives around the field, honey bees can move a long distance for nectar and any flowering canola field is likely to have honey bees in the field. So it is good to take these precautions. Spraying at these times will not reduce the effectiveness of the application, and for some of the insecticides that do not perform as well at higher temperatures, spraying late in the day or very early can increase effectiveness.

Sunflowers

Insects on sunflower heads: Some are noticing lygus bugs on the heads of sunflowers. High levels have been reported in the MacGregor area. Lygus bugs have many hosts, so levels in sunflowers may partially depend on the stages of some of these alternate hosts in the area, the stage of lygus in their lifecycle, and whether they have incentive to search for alternate hosts because of overly-mature or harvested crops. Alfalfa, canola, and beans are some of the other crops lygus bugs will feed on. So far there have been no reports of seed weevils in the sunflowers. Pheromone-baited traps for banded sunflower moth are catching adult moths.

Lygus bug nymph Adult lygus bug

It is very important in sunflowers that the same precautions to preserve honey bees mentioned above for canola are also followed if applying insecticides to sunflowers. As well as preserving the bees, pollinators can result in a very significant increase in sunflower yield, even in hybrid varieties.

Pulse Crops

Soybean aphids on soybeans: Low levels of soybean aphids were reported over the past week in soybean fields near Lowe Farm, Aubigny, and Winkler. Thanks to the local farm production advisors and Cargill agronomists for their keen scouting to notice this. So far levels are quite low; only the occasional one noticed after lots of scouting. Soybean fields should be scouted for soybean aphids, and levels monitored. A reminder though, that it takes a lot of soybean aphids per plant for populations to do enough damage to make an insecticide application economical. The economic threshold for soybean aphids is when there are at least 250 aphids per plant and the population is increasing, and the plants are in the R1 (beginning bloom) to R5 (beginning seed) growth stages. Below is a picture of soybean aphids on a soybean leaf; taken last year when populations were considerably higher than what we are currently seeing. The white specks are shed skins of the aphids.

Soybean aphids

Cereals

Slugs: More feeding by slugs on wheat has been reported from the Dauphin area. Feeding is generally close to the field edge, where they move into the crop from the dense vegetation along ditches. However, in one of the wheat fields in the Dauphin area about 30 acres have been affected, and on some plants the flag leaves were damaged.

 

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. The only trap to have cumulative counts in the uncertain risk range is a trap near Benito. Although it is still good to look for feeding by bertha armyworms or the larvae on the ground while doing general field scouting in canola, the risk of economic problems this year is generally low. Extra attention to looking for bertha armyworm larvae and their feeding is advised for those scouting canola in the Benito area. The table below shows the cumulative counts as of data reported July 26th.

 

Location of trap

Recent Count

Total count since Early-June

Benito

138

689

Pilot Mound

88

276

Carberry

70

219

Neepawa

21

165

Inglis

121

121

Hamiota

18

121

MacGregor

10

117

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

Note that the trapping period for adult moths of bertha armyworms is now done. Traps can be pulled from the field after counts are done this week.