What is in this article?:
- Plan ahead for corn earworm management in soybeans
- Online threshold information
• Corn earworm has been our most consistent soybean insect pest, sprayed on the majority of our acres in most years.
• I am predicting this year’s pressure will be similar to last year, which is to say relatively light.
Online threshold information
• 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.
• If you have reached threshold, you should spray. Keep an eye on blog posts for reports of pyrethroid-resistant moths in the system. Populations of these are spotty and not widespread across the state. If significant resistance is found, you should not spray a pyrethroid (common chemical names include beta-cyfluthrin, bifenthrin, lamda-cyhalothrin, zeta-cypermethrin).
Furthermore, if you have a control failure with a pyrethroid, do not spray with a pyrethroid again or with a pre-mixed product that does not contain a chemical effective against corn earworm. Don’t forget that sometimes what we think is “corn earworm” might actually be tobacco budworm, a similar looking species that is difficult to control with pyrethroids.
Other chemicals you should consider are the diamides, like Belt and Prevathon. Syngenta has a new registration for Besiege, which is a pre-mixed product containing the active ingredient of Prevathon plus a pyrethroid (lambda-cyhalothrin, aka Karate).
Blackhawk (Tracer) offers a unique chemistry class, the spinosyns, and is highly effective against corn earworm.
Finally, in every trial I’ve had it and at every rate (as low as 6.7 ounces per acre), 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. 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.
(For more on North Carolina field crops, visit http://www.nccrops.com/).
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