Alabama: Scout Late-Soybeans for Loopers, Whiteflies a Threat to Cotton

During the 3rd week of August cotton bollworm (CBW) moth trap catch numbers increased significantly over the previous week in Baldwin and Escambia Counties and declined in Autauga and Limestone Counties. Tobacco budworm (TBW) moth trap catches increased in Henry and Elmore Counties and declined in Limestone County.

Soybean looper moth trap catches increased at 4 of the 5 trapping sites with Autauga County having the highest number trapped this year for any site with 750 moths counted.

Early planted cotton is cutting out and many fields are either deemed to be safe from insect injury or will be checked for insects for one to two more weeks. One field in the Wiregrass region had 60% open bolls this week. Late planted fields of cotton still could see CBW and stinkbug injury.

CBW (=soybean pod worm) numbers are starting to decline (presently) in some soybeans in north Alabama. A few fields of double-cropped soybeans were sprayed specifically for CBW’s in north Alabama in early- to mid-August, but numbers in soybeans currently are dropping.

Numbers of CBW’s in late-planted soybeans at the Fairhope and Brewton stations were very low on 8/21 but the report for commercial fields in the Baldwin County area indicated CBW’s composed a significant portion of the mixed population of caterpillars feeding on soybeans and peanuts. CBW’s and southern armyworms have been a more important component of the mixture of worms on peanuts than in soybeans in extreme southwest Alabama.

A report from the Blackbelt portion of the state also indicated that southern armyworms were the predominant armyworm in row crops presently. The caterpillar complex on peanuts and soybeans in SW AL and the Blackbelt also includes velvetbean caterpillars (VBC) and green cloverworms.

Pretty much all the different products labeled for caterpillar control are being used in SW Alabama. Soybean loopers and velvetbean caterpillars had combined to cause 20 to 25% defoliation in one untreated plot of late July planted soybeans at the Fairhope Research Station on 8/21. Similar defoliation levels were observed in unsprayed test plots at the Brewton Research Station on 8/25.

We have reports of increasing numbers of soybean loopers in double-cropped soybeans in northwest and north central Alabama and Lamar County. Growers statewide need to check their late-planted soybeans for soybean loopers and other caterpillars.

Variables to consider when selecting an insecticide for soybean looper control are as follows:

The 5 oz/acre rate of Intrepid (methoxyfenozide) has been effective in controlling SBL but it is slower in killing loopers than the 5 oz/acre rate of Intrepid Edge (methoxyfenozide + spinetoram).

However, both Intrepid and Intrepid Edge had less than 5% defoliation 5 days after application in the Brewton trial in 2016. Control plots averaged 10% defoliation 5 DAA. If stinkbugs, 3-cornered alfalfa hoppers or kudzu bugs are also threatening yields you will need to add 6.4 oz/acre of bifenthrin to the Intrepid/Intrepid Edge.

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Prevathon (chlorantraniloprole) to date has given effective control of SBL’s. The lowest recommended labeled rate of Prevathon is 14 oz/acre. You will also need to add bifenthrin to the Prevathon to control sucking insects. Besiege contains both chlorantraniloprole and the pyrethroid lambda-cyhalothrin which at the 10 oz/acre rate provides 0.03 pounds a.i./acre of lambda-cy and will help control stink bugs and other sucking pests. Besiege is labeled for SBL control on soybeans at a rate of 10 oz/acre.

All of these products provided 30 days of residual control for VBC in our 2016 soybean caterpillar insecticide trial at Brewton. We have not seen soybean looper populations exceed the economic threshold for more than 2 weeks in Alabama in recent years. Intrepid, Intrepid Edge Prevathon and Besiege have all shown good rainfastness.

The emergency Extension meeting held at the Wiregrass Research and Extension Center on August 24 provided 40 attendees with the latest information on the silverleaf whitefly (SLWF) threat to cotton in southeast Alabama. You can see a video of this meeting here.

The SLWF is more likely to be a serious pest on late-planted cotton. The severe shortage of the most effective control options (Knack and Courier) and the difficulty in controlling this pest once the infestation has become well established are two major obstacles confronting SE AL cotton producers. More useful information about SLWF can be found here.

Reports indicate that the SLWF infestation area is expanding both northward into Barbour County and westward into Covington County in the Wiregrass. Soybeans and peanuts are also being infested with SLWF’s. Products that have shown activity and are recommended for control of the SLWF on cotton are Knack, Courier, Assail, Sivanto, Venom, and Oberon.

Products labeled for use on soybeans include Knack and Sivanto. If you need help in making treatment decisions for insect pests of cotton and soybeans please contact Tim Reed at 256-627-3450 or Ron Smith 334-332-9501.


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