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Agronomic Crops > Crops Blog > Posts > Soybean Loopers May Cause Problems for Later-Planted Soybean

August 26, 2018: So far numbers of acres treated for soybean loopers (SBL's) are less than normal in Alabama but the recent statewide increase in SBL moth trap catch numbers and the increase in the number of small SBL's in test plots in Baldwin and Escambia counties indicate the possibility of more fields requiring treatment during the next two weeks.

Soybean looper moth trap catches at 5 trapping sites in the state have increased steadily since the last week of July. (See Table below).  


Average trap catch numbers for 5 sites were as follows:  4th week of July = 102, 1st week of August = 135, 2nd week of August = 188; and 3rd week of August = 297.  Soybean loopers have been sprayed in most soybean fields in Baldwin county and numbers of small loopers present in test plots at Fairhope having soybeans in the early R5 stage have increased significantly during the past week. These plots were treated earlier with a foliar neonicotinoid spray and Amdro fire-ant bait to reduce beneficals, but unsprayed fields of soybeans at the Fairhope research station also had defoliation levels of 20% due to SBL's on August 23. Drop cloth samples taken on 8/23 showed total numbers of SBL's per 3 row  ft ranging from 55 to 80 at Fairhope. About 75% of these larvae were 3rd instars or younger and defoliation was close to 10%. This was up from 5% the previous week. SBL numbers at the Brewton station were also increasing with unsprayed test plots averaging 38 SBL larvae per 3 row feet with 75% of the worms being small. Defoliation averaged 5% to 10% in these Brewton plots, up from 1 to 4% the previous week. We have also had reports of SBL's being sprayed in Pickens, Dallas and Jackson counties. Reports from Monroe county, northwest and north central AL indicate very low levels of loopers present to date. Reports indicate Green cloverworm numbers have also crashed across the state after reaching treatable levels in some fields.  Velvetbean caterpillars were very rare at both Fairhope and Brewton on the 23rd and 24th of August, respectively. Our 2018 insecticide tests at Brewton have shown that Besiege, Intrepid Edge and Prevathon have all provided good control of soybean loopers at this site.  We have also had reports of Fall armyworms infesting pastures/hayfields, athletic fields and lawns across central and south Alabama. Grass that has been well-fertilized and watered is especially attractive to Fall armyworms.

Tim Reed, Extension Entomologist and Ron Smith Professor Emeritus of Entomology

 


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