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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect Update

July 14, 2008                   

Compiled by: John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives,
Crops Knowledge Centre, Phone: 204-745-5668; Fax: 204-745-5690

To report observations of insect activity or control that may be of interest or importance to others in Manitoba, please send messages to the above contact addresses.

To be placed on an e-mail list to be notified when new Manitoba Insect Updates are posted, please contact John Gavloski at the address or numbers listed above.


Summary

Alfalfa weevils continues to be a concern on alfalfa, but larvae are now starting to pupate. Grasshoppers are a concern in localized areas and some controls have been applied. Wheat midge continue to emerge, but high numbers have not yet been reported. 

Recent Insect Concerns and Observations

Alfalfa weevil feeding continues: Damage to alfalfa by alfalfa weevil continues to occur in many areas. Many parts of the Interlake have high levels, but high levels of alfalfa weevil have also been reported near Lac du Bonnet, Virden and Minnedosa. Larvae are starting to pupate, so the feeding damage should start to naturally decrease.

Grasshoppers: Grasshoppers are numerous in localized areas across the province, and some insecticides are being applied to control them. In many cases the high numbers are still concentrated around field edges. Many grasshoppers are in the 3rd and 4th instars, and some fifth instars are showing up in the population. Twostripped grasshopper seems to be our dominant species in many areas, with some migratory grasshopper mixed in. A reminder that now is a good time to be assessing grasshopper populations and applying controls if populations are high. Once grasshoppers become adults (with fully developed wings), control becomes much more difficult.

Aster Leafhopper Update: So far, levels of aster leafhoppers have been low in Manitoba. So the risk of aster yellows being of concern is much less than in 2007.

Surveys and Forecasts

Bertha Armyworm: Highest trap counts so far are 588 (Virden) and 455 (Minitonas). Counts in this range put these regions in a risk category labeled “Uncertain”; where infestations may not be widespread, but fields that were particularly attractive to egg-laying females could be infested. Moth counts could continue to get higher over the next couple of weeks. Data from the bertha armyworm adult monitoring program are available at:

https://www.gov.mb.ca/agriculture/crops/insects/bertha/index.html

 

Crop Scouting Reminders

Pea and flax are both flowering. Flowering is the preferred time to be scouting for aphids in these crops.

In flax, it is recommended to look for aphids when the crop is in full bloom, and again in the green boll stage. Economic thresholds are about 3 aphids per main stem on average at full bloom, and 8 aphids per main stem on average in the green boll stage.

Peas should be monitored for aphids at the beginning of flowering either by using a sweep net or checking the upper 20 cm of the plant tips. Economic thresholds are 9 to 12 aphids per sweep, or 2-3 aphids per 20 cm plant tip on average.  If economic thresholds are exceeded, the ideal timing to apply controls would be when 50% of the plants have produced some young pods.

 

Fusarium Head Blight Risk

Fusarium head blight risk should be considered now.

If your spring wheat or barley has yet to flower, you should be aware that the risk of Fusarium head blight is significant throughout much of Manitoba (less so in the SW corner).  The model that MAFRI uses looks back at the past seven days and measures number of hours in which rainfall occurred and number of hours when temperatures are in “the zone” most favorable for FHB infection – 15 to 30CInfection is likely when those temperatures coincide with high relative humidity.  Currently, this is occurring for brief periods in the evening and in the morning.  Check back on the forecast daily to get a sense of whether risk in your area is rising or falling.  The animation on the forecast shows how quickly this can happen.

 

Insect Identification Quiz

Photo by Denis Vermette

Question: While sweeping in cereal crops this past week, an agronomist found these flies (see Figure 1) in wheat and barley at about 4-5 per 10 sweeps.  What are they and are they of any concern?

Answer: The metallic flies with long legs in this figure are long-legged flies. They are predators of other insects. Most long-legged flies specialize on soft-bodied prey, such as small flies, aphids, thrips, etc. So obviously these are beneficial to have in the field. Long-legged flies can be quite abundant, so it is good if farmers and crop scouts know what they are.