2018
Refinement/validation of soybean looper thresholds in Miss. Soybeans
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Contributor/Checkoff:
Mississippi Soybean Promotion Board
Category:
Sustainable Production
Keywords:
GeneticsGenomicsSeed quality
Parent Project:
This is the first year of this project.
Lead Principal Investigator:
Don Cook, Mississippi State University
Co-Principal Investigators:
Project Code:
Contributing Organization (Checkoff):
Mississippi Soybean Promotion Board
$52,338
Institution Funded:
Mississippi State University Delta Research and Extension Center
$52,338
Brief Project Summary:

Soybean looper has become a significant annual pest of soybeans in Mississippi. The current action threshold for soybean looper infesting reproductive stage soybeans in Mississippi is 8 larvae one half inch or longer per row foot using drop cloth sampling or 19 larvae one half inch or longer using sweep net sampling. The first objective is to refine/validate the treatment threshold for soybean looper infesting soybeans in Mississippi. This project evaluates alternative insecticides (non-Diamide products) for soybean looper management and monitor the response of soybean looper populations from Mississippi soybeans to Diamide insecticides in laboratory assays.

Key Benefactors:
farmers, agronomists, extension agents

Information And Results
Final Project Results

Results were also presented at >40 grower meetings throughout the state of Mississippi during the winter/spring of 2017 and 2018.

Objective 1 Results
For every looper larva collected with a drop cloth, 0.44 was collected with a sweep net. For larvae =3rdinstar collected with a drop cloth, 0.89 larva was collected using a sweep net.

For every increase of 1 <3rdinstar larva per 25sweeps, defoliation increased 0.40%. For every increase of 1 =3rdinstar larva per 25 sweeps, defoliation increased 0.66%. For every increase of 1 total looper larva per 25 sweeps, defoliation increased 0.42%. Based on these results, 14 soybean looper larvae =3rdinstar and 20 total larvae would result in 20% defoliation.Fifth instar larvae consumed a greater percentage of leaf area compared to 1stto 4thinstar larvae.

Fourth instar larvae consumed a greater percentage of leaf area compared to 1stto 3rdinstar larvae. Fourth instar larvae consumed a greater total amount of leaf area compared to larvae of other sizes.

Objective 2 Results
All insecticide treatments resulted in significantly higher soybean yield compared to that from the non-treated control. Plots treated with Prevathon (20 oz/acre, diamide) had significantly higher yields than plots treated with Radiant (2 oz/acre, spinosyn) or Prevathon (14 oz/acre, diamide).In a second study, all insecticide treatments resulted in significantly lower densities of soybean looper compared to the non-treated control at 3, 6, and 10 days after treatment (DAT). Also, Intrepid Edge (IGR and spinosyn) resulted in significantly fewer soybean loopers per 25 sweeps compared to Diamond (IGR) at 3 DAT. All of the insecticide treatments resulted in significantly higher yields compared to the non-treated control. In a third study, all of the insecticide treatments resulted in significantly lower densities of soybean looper compared to the non-treated control at 3, 6, and 10 DAT, except Cavalier (IGR) at 3 and 10 DAT. At 10 DAT, Intrepid Edge (IGR and spinosyn) resulted in significantly fewer larvaethan any of the other insecticide treatments. Only Intrepid Edge (IGR and spinosyn) and Prevathon (diamide) resulted in significantly higher yields compared to the non-treated control.During 2018 only one trial was conducted due to frequent rainfall andwidespread natural disease infections in soybean looper populations.Disease ncidence was widespread and most larvae collected were =4thinstar. Defoliation did not reach 20% in any of the plots. There were no significant differences among treatments for yield.

Objective 3 Results
Soybean looper infestations did not persist in fields for an extended period of time during both 2017 and 2018. The unusually high rainfall during Augustthrough Septemberof both years and a tropical system during August2017 triggered outbreaks of multiple diseases in soybean looper populations. These diseases caused soybean looper densities to decline rapidly to almost non-existent levels. Disease prevalence (both fungal and viral) in all looper collections was very high. Greater than 95% mortality was observed before insects reached the adult stage. Therefore, no larvae were produced to conduct the laboratory insecticide response assays and no assays could be conducted.

The United Soybean Research Retention policy will display final reports with the project once completed but working files will be purged after three years. And financial information after seven years. All pertinent information is in the final report or if you want more information, please contact the project lead at your state soybean organization or principal investigator listed on the project.