Thursday, September 2, 2010

Soybean Loopers Turning Up In Higher-Than-Normal Numbers And On A Wide Basis

From Ames Herbert, Virginia Tech Extension Entomologist

Soybean loopers are now being reported in soybean fields across much of the eastern side of the state. In past years they were mostly confined to southeastern counties. This infestation has broken all the records in terms of intensity (as many as 100+/15 sweeps in some fields) and geography (now being reported from Middle Peninsula and Northern Neck counties).

This must be due to the persistent hot, dry weather, and the high percentage of fields previously treated with insecticides. Loopers are easy to identify but there is some confusion about their color. Soybean loopers have both a "green" and a "black" color phase (see images in this PowerPoint file). 

We are seeing both color phases in our samples. There may be some cabbage loopers (a completely different species) mixed in, but we have not verified this. There are no exact thresholds for loopers in soybean, so treatment should be based on the amount of leaf feeding in relation to the size of the total canopy. 

But, a very loose rule of thumb could be that 20 or more per 15 sweep net sweeps may constitute a threat. 

Fewer than that, especially in tall, full canopy fields probably does not constitute a threat. Some fields are getting close to maturity with pods and leaves beginning to yellow. Loopers are not a threat to those fields. 

Pyrethroids should not be figured into a looper treatment decision. They are less than effective. If stink bugs are present in looper infested fields, I would consider adding Orthene to the looper insecticide. 

Orthene will provide good control of both green and brown stink bugs where the pyrethroid would miss some of the browns. Oddly, we are seeing more brown stink bugs in some fields than greens, which is opposite of what we are used to seeing. 

We have initiated 5 different field trials to evaluate the effectiveness of many different insecticides/rates for loopers. Results will be presented at our annual Pre-Harvest Field Tour scheduled for Sept. 14.

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