Now is the time to scout fields for soybean aphids. Populations of this tiny yield-robbing insect can explode and reach the economic threshold before you realize it—if weather conditions are favorable.
Last week conditions in Minnesota were very good for soybean aphid reproduction. With those conditions the populations increased rapidly in many locations throughout Minnesota. "In Iowa we have been expecting 2008 soybean aphid populations to be lower than they were in 2004 and 2006 but the weather in 2008 hasn't been exactly typical," says ISU Extension entomologist Jon Tollefson.
Treat if aphids reach threshold
The increase in aphid numbers in states north of Iowa serve as a reminder that this is the time that you must be scouting soybeans at least once a week to keep an eye on this tiny pest. If aphid infestations reach the threshold, you should apply an insecticide treatment right away.
What about today's high soybean prices? Does that change the economic threshold treatment level from what you've used in past years? "The treatment threshold should remain at an average of 250 aphids per plant, even with increased value of soybeans," says Tollefson.
This is discussed in an article on ISU's Integrated Crop Management News website http://www.extension.iastate.edu/CropNews/2008/0730tollefsonriceoneal.htm
How to scout for soybean aphid
The scouting technique to use to monitor aphid numbers in fields is described in an article in a July 2007 ISU ICM newsletter. It is available on the ISU Website.
However, there is a faster scouting method you can use to make an aphid management decision for soybeans. Called the "Speed Scouting" technique, it is described in that same article as well. Information is also available in a free quick field guide focusing on how to use this "speed scouting" method.
Field Guides are now available
Knowing how to manage and "speed scout" soybean aphids just got easier, thanks to two new pocket-sized publications authored by ISU Extension entomologists Marlin Rice and Matt O'Neal.
The two companion soybean aphid publications are now "right off the press" and are available from ISU Extension.
One is a spiral-bound "Soybean Aphid Management Field Guide for 2008." This publication is identified by Extension number CSI 11. The 43-page pocket guide focuses on managing soybean aphid in Iowa. The guide is a handy reference to history, identification, development and management strategies for this relatively new insect to Iowa.
The second publication, "Speed Scouting of Soybean Aphids" is a double-sided card useful for field-by-field evaluation of soybean aphid populations. It uses the speed scouting technique recently developed by entomologists at University of Minnesota.
You can get your own copy
To get a copy of these references, as well as the publication "Soybean Disease and Pest Management" field guide (CSI 10), they are available for no charge from the ISU Extension Distribution Center at http://www.extension.iastate.edu/Store/ Look for the following:
• CSI 10 "Soybean Disease and Pest Management" field guide
• CSI 11 "Soybean Aphid Management" field guide
• CSI 15 "Speed Scouting—Soybean Aphids" field card
All three publications are produced and funded for no-cost distribution to Iowa farmers. Funding was provided by the Iowa Soybean Association.