Cryolite

During the course of investigations during the war period to develop insecticides from new materials, several hundred chemicals and combinations of chemicals were tested. This work was accentuated because of the shortage of pyrethrum, rotenone, and the arsenicals. Fluorine compounds were in good supply. One of these, cryolite or sodium,

fluoaluminate, recognized for many years as having possibilities as an insecticide, was experimented with extensively. Emphasis was placed or, the improvement of its dusting qualities and on the determination of the most effective strength and dosage per acre to use against various vegetable pests. As a substitute for calcium arsenate it was found that, under conditions in southern California, a cryolite dust mixture containing 70 percent of sodium fluoaluminate with talc as the diluent gave satisfactory control of the tomato pinworm and the tomato fruitworm. In the same area a mixture containing equal parts of sodium fluoaluminate and talc yielded good control of the pepper weevil. It was necessary, however, to establish a special washing device to remove the cryolite residues from the peppers.

In the Yakima Valley of Washington, where a cryolite dust mixture containing 55 percent of sodium fluoaluminate with pyrophyllite was used, 95 percent of the potato tubers were not damaged by the tuber flea beetle larva.

In eastern Virginia a satisfactory control of the corn earworm on late beans was obtained with two applications of a cryolite mixture containing 70 percent of sodium fluoaluminate with sulfur.

It was also found that sodium fluosilicate, a close relative of cryolite, in a wheat-bran bait was more effective than calcium arsenate against the Puerto Rican mole cricket and would also poison the southern mole cricket, a species not affected by a bait containing calcium arsenate. An effective bait against both species consisted of 8 pounds of sodium fluosilicate to 100 pounds of dry wheat bran, applied once at the rate of 20 pounds to the acre.

DDT as an Insecticide for Vegetables Investigations on the use of DDT as an insecticide for vegetables from the fall of 1942 to the spring of 1946 have led to the following conclusions: This chemical in its various formulations, including dust mixtures, emulsions, wettable powders, and aerosols, is toxic to a wide variety of insects. However, the range of usefulness of DDT is limited because of the residue factor. Its performance against several pests of potatoes, such as the potato leafhopper, the Colorado potato beetle, potato flea beetles, aphids, and psyllids, has been outstanding. It can be used with bordeaux mixture and the other so-called basic coppers. From the present knowledge it should not be used with copper-lime dusts, that is, mixtures of dehydrated copper sulfate and lime.

As an insecticide for tomatoes in southern California, DDT has proved to be more effective than either cryolite or calcium arsenate against the tomato fruitworm, and it is compatible with sulfur. Therefore, mixtures of DDT and sulfur can be used for the control of both the tomato fruitworm and the russet mite.

Its usefulness on beans is limited, as it will not control the Mexican bean beetle, although it is effective against the bean leafhopper and the corn earworm. The earworm attacks the tender shoots, flowers, and pods of snap and lima beans in some sections of the country.

On cabbage it has given a high degree of control of the various caterpillars, including the cabbage webworm and some kinds of cutworms, which attack cabbage in the South and oftentimes are destructive to the cabbage crop. However, because of the residue factor, the precaution must be followed that is necessary with arsenicals; that is, the crop should not be treated when there is foliage on the plant that will remain on the product prepared for market.

On peas the control of the pea weevil with DDT has been equal, if not superior, to that obtained with rotenone. In the dust, emulsion, and aerosol forms it has yielded more satisfactory control of the pea aphid than any material tested heretofore. However, the use of DDT on the pea crop both for pea weevil and pea aphid control is recommended with the reservation that pea vines be withheld from livestock until more is known about the residue hazard.

On onions DDT has given a slightly higher degree of onion thrips control than either nicotine or tartar emetic-sugar mixture.

Against the pepper weevil dust mixtures containing from 2 to 5 percent of DDT have given excellent control and have also controlled the green peach aphid, which often causes damage in pepper fields following the use of either calcium arsenate or cryolite.

As an insecticide for cucurbits (squash, pumpkins, cantaloupes, watermelons, and cucumbers) the indications are that the usefulness of DDT will be limited, because it is injurious to some of these crops, particularly certain varieties of squash.

DDT has been tested on a wide variety of vegetable plants for plant tolerance and, with the exception of the cucurbits, it appears that in most sections of the United States the insecticide can be used without injury to the crop. However, injury to peas and tomatoes has been reported from New Jersey.

DDT in aerosol form has been tested extensively in Maryland against the pea aphid, and this method of applying DDT to the pea crop appears to have a decided advantage over other methods because of the lightness of the load. However, analyses of residues on pea vines indicate that there is a greater residue from the aerosol treatment than from the use of dusts or emulsions, which may prohibit the use of DDT in the aerosol form on peas where the vines are to be used as cattle feed.

DDT as a soil insecticide has been tested against wireworms, and while it is slow acting against these pests, the indications are that it may be useful as a means of keeping wireworm infestations to a minimum.

Sabadilla and Soil Fumigants

Sabadilla was introduced into the vegetable-insecticide field during the war by T. C. Allen, of the University of Wisconsin. Sabadilla insecticides are prepared from the ground seed of a tropical lily or lilies. The active principle of the seeds is a complex mixture of alkaloids called veratrine. This material. appears to have its greatest usefulness in the control of the squash bug, harlequin bug, and the potato or bean leafhopper.

Following the successful use of a mixture of dichloropropane and dichloropropene, known commercially as D-D, for nematode control in pineapple plantings in Hawaii, by Walter Carter, of the Pineapple Growers Association, this material was tested in California and Washington against wireworms. The results were promising. Another product having for its toxic agent ethylene dibromide gave equally good, if not superior, results against the sugar-beet wireworm. Success in the use of a soil fumigant is dependent on the method of application, and within the last 2 years machines for effectively applying soil fumigants have been developed. This, together with more effective soil fumigants, should aid materially in reducing wireworm infestations in lands devoted to vegetables where the returns per acre will justify a comparatively large output of funds.

THE AUTHOR

W. H. White is in charge of the Division of Truck Crop and Garden Insect Investigations in the Bureau of Entomology and Plant Quarantine.