Masters Theses

Date of Award

12-1987

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

William A. Krueger

Committee Members

Neil Rhodes Jr., Elmer Ashburn

Abstract

Field and greenhouse experiments to investigate the behavior and control of sicklepod (Cassia obtusifolia L.) in soybeans (Glycine max L.) were conducted from 1985 to 1987. A survey of sicklepod distribution and control in Tennessee was also conducted. Sicklepod is present in 86% of the counties in Tennessee with the heaviest infestations in the western portion of the state. Sicklepod is a threat to crop yields in 62% of Tennessee's counties and infests over 100,000 ha of cropland. Sicklepod infestations are increasing, but the problem is not as severe as some of Tennessee's most damaging agronomic weeds such as annual morningglory (Ipomoea spp. ) , common cocklebur (Xanthium strumarium L.) , and johnsongrass [Sorghum halepense (L.) Pers.]. Atrazine and imazaquin are the most commonly used herbicides for sicklepod control in Tennessee. Alachlor plus metribuzin applied preemergence and the following sequential (preemergence followed by postemergence) applications: metribuzin followed by chlorimuron, chlorimuron plus metribuzin followed by chlorimuron, imazaquin followed by imazaquin, and imazethapyr followed by imazethapyr, were evaluated for their effects on sicklepod. Conventional and no-tillage cropping systems were also compared. All herbicide programs reduced sicklepod number and height compared to the weedy checks. The addition of a postemergence herbicide improved sicklepod control. Adequate sicklepod control was not obtained using any of the tested herbicides. Sicklepod numbers were greater in conventional tillage while sicklepod height was greater in no-tillage. Sicklepod control obtained relative to each cropping system varied with location. Soybean injury was noted with several herbicides in no-tillage. Spring oats (Avena sativa L.) were evaluated for allelopathic effects on sicklepod. A spring oat mulch lowered sicklepod dry weight production. Residues left by spring oats lowered sicklepod shoot length and root dry weight. Sicklepod was evaluated for allelopathic effects on soybeans. Sicklepod residues lowered soybean leaf area. Soybeans planted into soil in which sicklepod had previously been grown had lower shoot lengths, leaf areas, and dry weights compared to the controls. The effects of chlorimuron and imazaquin mixed with metribuzin and applied preemergence to sicklepod were evaluated under greenhouse conditions. Metribuzin mixed with chlorimuron gave up to 54% less control when measured by sicklepod number and up to 26% less control when measured by sicklepod dry weight than did metribuzin applied alone. Metribuzin mixed with imazaquin gave up to 57% less control when measured by sicklepod number and up to 33% less control when measured by sicklepod dry weight than did metribuzin applied alone.

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