MANY INSECTICIDES and mixtures of insecticides have been tested.

Years ago calcium arsenate was tried and found so effective that it remained the No. 1 boll weevil poison until the organic insecticides became available in 1947 and 1948.

Calcium arsenate usually causes an increase of the cotton aphid. After several years of experimentation, a mixture of calcium arsenate containing 2 percent of nicotine in alternate applications was recommended in 1940. The mixture was very effective against the boll weevil and cotton aphid when properly applied, but the Supply of nicotine was so limited that the program could not be put into effect in all of the areas where it could have been used successfully. In South Carolina, where the calcium arsenate residue in some soils caused injury to crops, the arsenic was reduced by using a mixture of calcium arsenate and lime. In some parts of Texas, where insects in addition to the boll weevil were involved, a mixture of calcium arsenate and sulfur was used.

DDT will not control the boll weevil. It often makes conditions favorable for the increase of cotton aphids and spider mites by reducing the numbers of their natural enemies. Since it is effective against the bollworm it has become essential in mixtures of insecticides now in general use on cotton.

Benzene hexachloride, first tested against cotton insects in 1945, was found to be effective against the boll weevil and other cotton pests. It failed to control the bollworm and spider mites, and often encouraged an increase in the number of those pests. Of the many combinations tested, a mixture isomer 3 percent of the gamma isomer of benzene hexachloride, 5 percent of DDT, and 40 percent of sulfur was one of the best. The benzene hexachloride kills the boll weevil, cotton aphid, tarnished and rapid plant bugs, cotton leafworm, thrips, southern green stink bug, garden web-worm, fall armyworm, cotton fleahopper, and grasshoppers. DDT kills the bollworm, pink bollworm, plant bugs, fleahoppers, and thrips. Sulfur prevents the development of injurious spider mite infestations. The extent to which sulfur is used primarily to control spider mites is shown by the fact that approximately 200 million pounds were dusted on cotton in 1950.

The benzene hexachloride in the mixture is a fast killer and kills as a vapor, by contact, and as a stomach poison. Alternate applications of this fast killer (which has a short residual effect) and calcium arsenate (a slow killer with long residual effect) make an effective control program.

Toxaphene has given excellent control of the boll weevil. It also controls many other cotton insect pests. Like DDT and benzene hexachloride, it may cause an increase of spider mites. In areas where mites are a problem, at least 40 percent of sulfur should be added.

Chlordane has given promising results in some tests against the boll weevil. But dusts containing as high as10 percent of the material have given varying results. Chlordane encourages the increase of bollworms and spider mites. When used in low concentrations it also causes an increase of the cotton aphid; therefore it has not been used extensively against the boll weevil.

Aldrin has been tested throughout the Cotton Belt. It is a good boll weevil poison if enough of it is used. Used alone, it will not control the bollworm and may cause an increase in the number of spider mites. Aldrin will not control heavy infestations of cotton aphids and in some instances it has caused an increase of aphids. DDT should be added to an aldrin mixture for control of bollworms, and sulfur should be added to prevent an increase of spider mites.

Dieldrin is a good boll weevil poison if used in sufficient quantity. DDT should be added to the dieldrin mixture to aid in the control of the bollworm; sulfur should be added to prevent an increase of spider mites.

Heptachlor has given excellent control of the boll weevil. DDT should be added to heptachlor mixtures for control of the bollworm, and sulfur should be added to prevent an increase of spider mites.

Each of these insecticides has its place in the boll weevil control program. Some are more effective in certain areas and under certain conditions than others. Intensive experimentation is necessary to determine the exact conditions and locations under which they may be most effective. In recent large-scale experiments, however, aldrin, benzene hexachloride, calcium arsenate, chlordane, dieldrin, heptachlor, and toxaphene all gave satisfactory boll weevil control when properly applied as needed.

EQUIPMENT AND METHODS for applying poisons to cotton for control of the boll weevil differ greatly. Dusting has long been more popular than spraying. Spraying cotton with the arsenicals has not proved profitable. However, experiments conducted in many areas in 1949 and 1950 indicated that some of the organic insecticides applied as spray emulsions at low pressure and volume per acre were effective against the boll weevil.

Hand gun, saddle gun, one-mule and wheel-barrow-type machines, traction-power cart machines, power-operated machines, and airplanes are the types of dusting machines in general use. Each type has its place. The sprayers in use are of two general types ground and airplane.

The cotton grower now has a wide selection of insecticides or combinations of insecticides which can be used to control the boll weevil, including dusts and sprays, which appear to be about equally effective. More important than this or than the method used are the proper time of starting applications, the correct interval between applications, favorable weather conditions, complete coverage, and the continuation of applications until the crop has matured.

R. C. GAINES is an entomologist in the Bureau of Entomology and Plant Quarantine. He was graduated from the Alabama Polytechnic Institute in 1920 and has been in the Bureau since September 1, 1920. In January 1931 he was put in charge of the laboratory of the division of cotton insect investigations in Tallulah, La.