Masters Theses

Date of Award

5-1998

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Gary L. Lentz

Committee Members

Jerome Grant, Charles Pless

Abstract

Production of cotton, an important commodity in the United States, provides fiber, oil, cottonseed meal for feed, and numerous jobs. In 1996, 217, 416 hectares of cotton were harvested in Tennessee, contributing approximately $260.3 million to the state's economy.

Cotton, a plant native to the West Indies, was introduced into the United States during colonial times. Some pests of cotton have been introduced on imported plants, while others use cotton as an alternate host, such as thrips (Thysanoptera: Thripidae). Thrips damage cotton by feeding on its tender terminal buds and leaves.

Thrips control options seem to be limited; therefore, control with chemical insecticides is widely practiced. Knowledge of the insecticides and their impact on thrips and plant parameters is important for recommending and selecting insecticides for early-season thrips control.

Because cotton is important to the nation's economy, and because of the impact of thrips, efficient means of control of these pests must be utilized. Research was conducted in Tennessee at the West Tennessee Experiment Station and the Milan Experiment Station in 1996 and 1997 to evaluate the impact of selected insecticides on thrips as well as cotton growth and development. The objectives of this research were to: 1) determine the efficacy of selected insecticides for early-season thrips control, 2) determine if the selected Insecticides affect stand, plant height, node of first position square, bloom count, and yield, and 3) compare a standard preemergent herbicide program versus the Roundup Ultra® program to determine if the preemergent herbicides affect cotton treated with phorate.

Efficacy tests showed that aldicarb provided consistent control of thrips. These tests also showed that Garlic Barrier + Fish Oil (1996) and Garlic Barrier + Fish Agra (1997) were consistent in failing to control thrips. In 1996, imidacloprid 480F ST provided poor control of thrips. Because plants emerged rapidly, the seed coats of plants treated with imidacloprid remained attached to the cotyledons leaving no insecticide in the soil for roots to absorb.

Insecticides applied for management of thrips may negatively affect plant growth and development. Stands were reduced among the plots containing imidacloprid and acephate seed treatments. Imidacloprid, phorate, and Garlic Barrier + Fish Oil/Agra treatments reduced plant heights, and phorate alone caused the node of first position square to be higher than the other treatments. Phorate also delayed bloom production. Lint yields were not consistently affected by chemical treatments. Phorate applied in combination with preemergent herbicides adversely affected plant growth and development. A reduction in stands was observed among the standard herbicide plots treated with phorate (1.68 kg Al/ha), and plant heights were decreased in these plots. The node of first position square was not different in the two herbicide programs. Bloom production was reduced by phorate (1.68 kg Al/ha) in the Roundup Ultra® plots, and by both high and low rates of phorate in the standard herbicide plots. Lint yields were higher in the phorate-treated Roundup Ultra® plots.

Early-season insecticides are valuable tools in thrips management. This research suggests that the insecticides which provide control of thrips may adversely affect plant growth and development, and preemergent herbicides combined with insecticides also may negatively impact plant growth and development. By monitoring the efficacy and negative effects of an insecticide, extension entomologists can use the results of this research to make recommendations for conventional cotton as well as transgenic cotton, i.e. Roundup Ready® cotton.

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