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The Alabama Crops Insect Report contains some the latest information on insect activity in the state’s major row crops. These updates come from members of the Alabama Cooperative Extension System agronomic crops team. For more information on row crops in Alabama, listen to the Alabama Crops Report Podcast and subscribe to the Alabama Crops Report Newsletter.


Soybeans

September 8, 2022 – Soybean Loopers and Velvetbean Caterpillars

by Scott Graham

A side-by-side image of a soybean looper and a velvetbean caterpillar.

Soybean Looper (left) and Velvetbean Caterpillars (right)

As the calendar turns to September, for Alabama cotton crops, most insect pressure is past, some are beginning to receive defoliation applications, and all are hoping for a dry fall for harvesting. With the cotton season mostly complete, the soybean insect situation is beginning to build.

Over the past week, Extension professionals have gotten several reports and phone calls about defoliating caterpillars in soybeans across central and northeast Alabama. While a complex of worms is in fields, soybean loopers (SBL) and velvetbean caterpillars (VBC) are the dominate and most important species in the mix. In addition to a detection technique (i.e., sweep net or drop cloth), looking at the defoliation within the plant canopy can give an idea as to which species is doing most of the damage.

  • VBC: four pair of prolegs, defoliation begins in the upper portion of the canopy
  • SBL: two pair of prolegs, defoliation begins in the lower portion of the canopy

A sweep net with caterpillar in it.There are a couple of thresholds to use based on scouting techniques for defoliating caterpillars. Prevent 20% defoliation during peak podfill (R1-R6). Prevent 30% defoliation from R6 to R6.5 (approximately seven to ten days). Alternatively, treat when 38 VBC or 19 SBL are found per 25 sweeps. As mentioned above, most fields will have a complex of worms, not just one or the other. Thus, detection techniques may be more useful for determining pest complex rather than treatment levels. Species composition is important for insecticide decisions. Another important reason for detection techniques is to get an idea of the size of the worms in the field. Like most things, VBCs and SBLs consume more food as they grow. In other words, larger worms eat more leaves (in a shorter amount of time) than smaller worms. If the majority of the population is made up of worms nearly 1 inch long or bigger, then action should be taken immediately. If most of the worms are small (less than 0.25 inch), then there is more time to make a spray.

Once the decision is made to treat, what are the options? There are several good materials to choose from, but considerations for what to choose involves pest complex, economics, and weather.

If soybean looper is the dominate pest, pyrethroids will do more harm than good. The options for soybean loopers include diamides (e.g. Besiege, Vantacor, Elevest) or Intrepid/Intrepid Edge. These products provide good initial and residual control of the spectrum of the defoliating caterpillar complex. While the mentioned options provide excellent control of VBC, most labeled pyrethroids and IGRs also provide control. One issue with pyrethroids is the lack of residual control. There have been instances in the past where multiple applications were required to manage VBC populations because of an extended migration over several weeks that would have likely been alleviated by a single initial application of a diamide.

If you would like to provide reports or observations on the insect situation from your region, contact Scott Graham at 662-809-3368 or scottg@auburn.edu or Ron Smith at 334-332-9501 or smithrh@auburn.edu.


Cotton

No updates at this time.


Corn

No updates at this time.


Peanuts

No updates at this time.


Trade and brand names used in this publication are given for information purposes only. No guarantee, endorsement, or discrimination among comparable products is intended or implied by the Alabama Cooperative Extension System.

 

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