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• Since the spray was a full rate of a pyrethroid, it is likely these insects are resistant to this chemical.
• We simply cannot predict the areas in which pyrethroids will fail.
• Weknow we have resistant worms in our system. The safe bet is to spray a chemical other than a pyrethroid.
Finally, in every trial I’ve had it and at every rate (as low as 6.7 oz/A), Steward, which is also a unique type of chemistry, has been the most effective or among the most effective chemical for corn earworm, even at lower rates.
Each product has advantages or disadvantages. For example, the residual of the diamides is very good, but may not be a concern since only one generation of corn earworm a year generally develops in soybeans.
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However, in some years (like 2010) we can have multiple infestations, as well as late-season pests, like soybean loopers and fall armyworms. These products are excellent choices in these situations.
Above all, rotate chemistry and only spray at threshold.
The threshold for corn earworm is online and can be accessed using arecently updated threshold calculator (click here). This threshold is specifically for podding soybeans (R4-R7). It also is accessible from mobile devices and can be used in the field.
This threshold is already conservative and there should be no need to adjust it. This is set below the break-even point where the cost of control is equal to the damage the worms are doing.
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