Masters Theses

Date of Award

6-1968

Degree Type

Thesis

Degree Name

Master of Science

Major

Biosystems Engineering

Major Professor

D. Houston Luttrell

Committee Members

John J. McDow, Stelmon E. Bennett

Abstract

The use of flame as a control for the alfalfa weevil, Hypera postica (Gyllenhal), has been known since 1910; however, it was not used extensively until the last few years. Previously, a chlorinated hydrocarbon insecticide, heptachlor, had been effectively used for weevil control. After restrictions were placed on heptachlor a tremendous increase in infestation of alfalfa fields by the alfalfa weevil occurred, and interest in flaming as a control was revived by researchers.

Dr. H. H. Tippins, University of Georgia, 1963, discovered the partial control of the weevil with flame when a fire accidentally broke out in some of his alfalfa plots. The research work in flame control for the weevil began at The University of Tennessee in 1964. Flaming alfalfa, followed with one spraying, is now the recommended practice for control of the weevil in Tennessee.

Knowledge of the life cycle of the weevil was necessary before it could be effectively controlled and sufficiently researched through flaming. The four stages of the weevil's life cycle are the egg, larva, pupa, and adult. The weevil is capable of wintering in both the egg and adult stages. However, the large number of eggs found in alfalfa stubble during the winter months indicate that the egg is the principal wintering stage (3).

The female deposits her eggs in the alfalfa stem in the fall and winter months, with some being laid in the new foliage during the early spring. The eggs number from one to forty, but usually average about a dozen in each deposit. The length of time required for the eggs to hatch depends primarily on the environmental temperatures (20). The eggs usually hatch from March until June in Tennessee. The young larvae move from the stubble base to the tender grow ing bud of the alfalfa. They grow from less than 1/16 inch in length at birth and grayish white in color to 1/h inch long and leaf-green when full-grown (17). After the larvae devour the leaf bud, they move to the open leaves, vigorously eating the selected soft tissue. Since the larva stage is the most destructive stage of the weevil, it is the one of primary importance. The larvae leave nothing except the woody fibers of the stem when they are left uncontrolled (20). The alfalfa fields take on a grayish appearance which resulted from the infestation of the larvae (17).

The larvae grow to maturity in about three to four weeks and move to the ground to spin loose, white cocoons, roughly spherical in shape, about the size of a small dried pea. The cocoons are usually found among the surface litter. After about ten days the adults emerge and feed on the alfalfa until high temperatures in the summer months cause them to seek shelter along the fence rows in the nearby woods (17).

The adult weevils notch main stems, sever side shoots and leaf stems, and feed upon the leaves. Their destructive behavior gives a ragged appearance to the field. The appearance of the older weevils is distinctive because their thorax bears a dark double-barred pattern separated by a narrow light-colored line. A single dark circle can be seen on either side of the thorax. Older weevils are usually darker in color than the young ones (17).

The female adult weevils move back to the field to begin laying their eggs with the return of cool weather in the fall. The weevils burrow in the soil around the crown of the alfalfa plants during extreme cold weather (20).

The majority of alfalfa flamers on the market burn propane gas and are recommended as a control of the weevil. Therefore, having a machine to perform at optimum efficiency is required to receive effective burning of the alfalfa weevil. If the burners on the machine could be adjusted to produce more thermal energy beneath the burners than the amount they are presently producing, while consuming the same volume of fuel, then the cost per acre for using the alfalfa flamers could be reduced. The problem for this thesis was to test the flamer design with respect to the positioning or location of the burners for temperature variation.

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