Summary
A new threshold was developed by UGA and cooperating southeastern entomologists for management of stink bugs in cotton. Research and threshold verification trials conducted in Georgia have demonstrated that net returns using a dynamic threshold may be increased by $19 per acre compared with previously recommended stink bug management programs.
Situation
Stink bugs are a serious pest of cotton in Georgia and the southeast. Stink bugs feed on developing bolls which results in reduced yield and fiber quality. Since the elimination of the boll weevil as an economic pest and the commercialization of transgenic Bt cotton, stink bugs have been the primary insect pest targeted by foliar insecticides in Georgia cotton. Annual insecticide use ranges from 0-5 applications per field and have averaged about two during recent years. For nearly a decade the decision to apply insecticides for stink bugs in cotton has been based on an economic threshold of 20 percent boll injury which remains constant or static throughout the season. UGA entomologists participated in a regional project with entomologists from southeastern cotton producing states with the objective of improving stink bug management in cotton. As part of the project, periods of maximum and minimum susceptibility of cotton to stink bugs were identified. Protection from stink bugs was most important during weeks 3-5 of bloom and less important during the first two weeks of bloom and after the 5th week of bloom. The results also showed that low stink bug levels early in the season suggested less protection was needed and greater numbers of large “bug safe” bolls later in the season also suggested less protection was needed. Based on these data and observation, a dynamic boll damage threshold approach was developed where allowable levels of boll damage change by plant developmental stage or week of bloom.
Response
Beginning in 2006, UGA and cooperating entomologists began evaluating a dynamic threshold which takes into account the varying degree of plant susceptibility or the number of susceptible bolls present during a given plant growth stage. The dynamic threshold raises allowable injury during the first two weeks of bloom and after the 5th week of bloom (few susceptible bolls present) and lowers the threshold during weeks 3-5 of bloom (many susceptible bolls present). During the last four years, 16 field experiments have been conducted in Georgia to evaluate and verify the new dynamic threshold approach. Treatments included an untreated control, 20 percent static threshold, dynamic threshold, and an aggressively sprayed treatment with the intent of eliminating stink bug damage. Net returns to management for the various treatments were calculated by multiplying the increased yield in treatments compared with the untreated by $0.59 per lb of lint and subtracting the costs of insecticide and application (number of applications multiplied by $9.00).
Impact
On average the greatest yield among treatments occurred when cotton was aggressively protected from stink bugs (sprayed weekly, 6.88 insecticide applications), however net return to the aggressively sprayed management program was only $12.76 per acre using this strategy due to the high cost of insecticide control. When thresholds were used, the number of insecticide applications was significantly less, 0.94 in the 20 percent threshold treatment and 1.56 in the dynamic threshold treatment. Although yields were slightly lower in threshold treatments compared with the aggressively protected treatment, net returns were increased. Net returns were $32.27 per acre for the 20 percent threshold and $51.58 when the dynamic threshold was used. The use of the dynamic threshold increased net return by over $19 per acre compared with the 20 percent static threshold which has been the standard threshold used for stink bug management in the southeast. A regional publication “Managing Stink Bugs in Cotton: Research in the Southeast Region” was published by cooperating entomologist from the southeast. This publication outlines the dynamic threshold approach and additional information related to stink bug management, biology and ecology. The publication has been printed and will be distributed to County Agents, growers, and industry representatives at production meetings this winter. Adoption and implementation of the dynamic threshold could have a significant economic impact to the Georgia cotton industry which plants about 1 million acres per year.
State Issue
Agricultural Profitability and Sustainability
Details
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Year:
2009
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Geographic Scope:
State
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County:
Tift
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Program Areas:
- Agriculture & Natural Resources
