The third week in June is normally when we can begin some expeditionary scouting for soybean aphid. Check a few of the fields that are normally infested early if you haven't already done so. Check field edges near buckthorn. If aphids are found, they are likely to be in the expanding leaf at the growing point of the plant.

Though there have been reports of fields with low levels of aphids in southern MN, they also had easily detectable aphids colonizing buckthorn last fall. NW MN had little to no detection of aphids colonizing buckthorn in the fall of ‘06. Quite a different picture when compared to the large aphid numbers we had on buckthorn in the fall of ‘05. With significantly fewer aphids on buckthorn last fall, the NW population should not have overwintered as eggs to the extent they did last season. Anticipate a much slower start to soybean aphids this year.

The economic threshold is still 250 soybean aphids/plant with 80% or more of the plants infested.  Soybeans can compensate for a variety of stresses during the vegetative stage and so can tolerate significant aphid pressure.  Aphid populations on vegetative stage soybeans can also be disrupted by heavy rainfall events and there is still a significant period of development during which predation has a chance to work.  Alate (winged) aphids are being produced now on more heavily infested plants and emigration can stagnate or collapse populations on early colonized fields. 

Regardless of product, insecticide residual will be very short on rapidly growing soybeans and new plant material added post application will not be protected.  In addition, early treated plants can be rapidly re-colonized.  Delaying control until needed makes good economic sense.