Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Catchot, Angus L., Jr.

Committee Member

Gore, Jeffrey

Committee Member

Cook, Donald R.

Committee Member

Musser, Fred R.

Committee Member

Irby, Jon Trenton

Other Advisors or Committee Members

Krutz, Larry J.

Date of Degree

5-4-2018

Document Type

Dissertation - Open Access

Major

Life Sciences (Entomology)

Degree Name

Doctor of Philosophy (Ph.D)

College

College of Agriculture and Life Sciences

Department

Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology

Abstract

Soybean, Glycine max (L.) Merr., is planted across a vast amount of land in the Mid-Southern U.S. (Arkansas, Louisiana, Mississippi, and Tennessee), and yield responses to defoliation can vary. Experiments were conducted during 2015-2017 evaluating how soybean yield responds to multiple and continuous defoliation, as well as planting date and plant population. Multiple defoliation events were evaluated by defoliating soybean at varying levels at V3, V6, and both growth stages. There was no interaction between defoliation occurring at V3 and V6 growth stages, indicating that the impact of each defoliation event was independent of the other. The effect of continuous defoliation was evaluated by defoliating soybean weekly, beginning at V2. Defoliation continued throughout the vegetative growth stages or throughout the entire growing season, and was compared to the same defoliation level occurring one time at R3. Continuous defoliation during vegetative growth stages only, did not reduce yield at any of the levels tested. Defoliation occurring throughout the growing season reduced yields more than a one-time defoliation event at R3, but only when defoliation levels exceeded the 20% defoliation threshold. This indicates that thresholds do not need to be modified to account for multiple or continuous defoliation. To evaluate the effect of planting date on yield loss from defoliation, soybean was planted at six planting dates beginning in early-April and continuing through mid-June. Each planting date included a defoliated treatment and an undefoliated control. It was determined that later planted soybean lose a greater amount of yield than earlier planted. Higher yielding soybean also lost more yield than lower yielding soybean at every planting date until Mid-June. It was concluded that late planted soybeans could benefit from a lower treatment threshold. The effect of plant population on yield loss from defoliation was evaluated by planting soybean at five populations ranging from 123,500 seeds/ha to 420,070 seeds/ha. A undefoliated control and a defoliated treatment was included for each plant population. Defoliation significantly reduced yields only where final plant populations were lower than 192,800 plants/ha. This indicates that fields with substandard plant populations are more susceptible to yield loss from defoliating pests.

URI

https://hdl.handle.net/11668/16983

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