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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect Update

August 18, 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

Soybean aphid numbers are still increasing in some fields and many soybean fields have been treated for soybean aphids over the past week.  

Recent Insect Concerns and Observations
 

Soybean Aphids: Soybean aphid populations continue to build and controls have been needed in many areas. High populations are now showing up in many of the soybean growing areas of Manitoba. Over the past week, economic populations have been noted or reported near Beausejour, Morris, St.Joseph, Roland, Brunkild, Pilot Mound, Portage la Prairie, Bagot, MacGregor, and Gladstone. So soybean growers and agronomists should make sure soybeans are being scouted for soybean aphids. More than one scouting trip will be needed to determine if the population is increasing (which is part of the information needed to properly use the economic threshold for soybean aphids).  

 

A reminder that when scouting for soybean aphids, when populations are high you will not be able to individually count soybean aphids. Such attempts would probably produce inaccurate numbers. You need to be able to estimate what levels are like. The scouting cards mentioned in the August 5th update are one tool to help you do this. It may be helpful to create categories for higher levels (such as 250-500; >500). Then it is a matter of having a close look at a plant and placing it in one of these categories, rather than worrying about whether the true level was 350 or 400. If 80% or more of the plants fall into the 250-500 or >500 categories, and levels have increased since last scouting, and plants are in the R1 (beginning bloom) to R5 (beginning pod) growth stages, then insecticide treatments are likely to be less costly than yield loss the aphids will cause.
   

Surveys and Forecasts

Grasshopper Survey: A reminder that throughout August a grasshopper survey is being conducted. Populations of grasshoppers are estimated to predict the risk for the next season. Staff from MAFRI traditionally do a lot of the counts for this survey, but if anyone is interested in providing estimates of grasshoppers in their area, or the farms or area they scout, this would be welcome. The protocol, data sheets, explanation of the grasshopper survey, and where to send data can be found at: https://www.gov.mb.ca/agriculture/crops/insects/fad95s00.html

So far there have been a wide range of counts in the survey; many counts are in the 6-8 / m2 range, with high counts of around 18 / m2.

Crop Scouting Reminders and Tips

The biggest insect concern to be scouting for now is soybean aphids in soybeans.

Confection sunflowers that are still in the early flowering stages should be scouted for lygus bugs and banded sunflower moth.

Insect Identification Quiz


Question: You are scouting for soybean aphids and notice these small white things that are quite abundant in the same location as the soybean aphid colonies. These are:

a)      Predators of the soybean aphid.

b)      Shed skins from the soybean aphids

c)      Albino soybean aphids

Answer: These white specks are the caste skins (cuticle) of soybean aphids. As insects grow they must shed their cuticle each time they pass to the next growth stage. With many aphids, these skins will remain on the plants they are on, giving the plants the appearance of having bad dandruff (in addition to aphids).