The incorporation of such stable insecticides as DDT and chlordane in the nursery soil has proved successful and has obviated much of the necessity for soil fumigation in relation to plant quarantine measures.

Fumigation of potting soil is likewise important in enforcing quarantines. Carbon disulfide, chloropicrin, and methyl bromide are used frequently to fumigate potting soil that is to be used under certified conditions.

Under the regulations that apply to plant products imported into the United States, fumigation is widely utilized on shrubs, trees, corms, bulbs, roots, tubers, cut flowers, seeds, restricted fruit and vegetable products, cotton byproducts, and broomcorn.

The summary we give below of imported material treated in 1949 and 1950, mostly by fumigation, indicates the scope of such fumigation.

Because of infestations with living giant African snails, even shiploads of steel scrap from islands in the South Pacific have been fumigated.

In 1918 quarantine inspectors began to fumigate American railway cars on their return from Mexico. Many of the cars were used to haul cottonseed or another cotton product in Mexico and became contaminated with Mexican cottonseed, which might contain live larvae of the pink bollworm. Large fumigation houses, ranging in capacity from 2 to 20 freight cars, were maintained at six border points to treat all returning cars. The largest house had a capacity of more than 200,000 cubic feet and required 80 to 120 pounds of liquid hydrocyanic acid for one fumigation. In 1949 the practice was discontinued except for special reasons, because the precautions taken in Mexico reduced to a negligible point the probability of contamination of cars with infested cottonseed.

Fumigation is also used under various domestic plant quarantines. Under Japanese beetle quarantine regulations, methyl bromide fumigation of fruits and vegetables to eliminate any live adults was the preferred practice for many years. As many as 5,000 freight-car loads a year were so treated in the 1940's. Since then the use of DDT dust has replaced some of this fumigation. One to two million nursery plants were also fumigated. Under white-fringed beetle quarantines, fumigation of balled and burlapped nursery plants has been practiced since 1939. Fumigation is used also to treat white potatoes, peanut hay, and lupine seed. To combat the sweetpotato weevil, fumigation has been required for table-stock sweetpotatoes that move from quarantined areas to other growing areas in the South.

Fumigation with methyl bromide has been adapted to the treatment of Christmas trees and greens cut in localities infested with gypsy moth. It destroys dormant egg clusters on the branches. Formerly the greens and trees had to be inspected one piece at a time.

Methyl bromide fumigation is used for treating cottonseed as an alternative to the long-standard heat treatment. Sacked cottonseed for planting can be fumigated in the manner usually practiced for most commodities, but cottonseed in bulk has to be fumigated under conditions of forced circulation in order to distribute the fumigant. To do that, special apparatus was devised to fit in with the normal handling practices of cottonseed. Large steel tanks, holding up to 600 tons of cottonseed, have blowers and a duct system that draw the fumigant down through seed more than 40 feet deep. The tanks are loaded and unloaded by mechanical conveyors commonly used in handling cottonseed. Fumigation is also done in freight cars by connecting a portable forced-circulation system, which operates outside the car, to flexible ducts attached to the floor and ceiling levels. More than 73,000 tons of cottonseed were fumigated in 1950 in storage tanks and more than 300 carloads were fumigated on a railroad siding. That is only a small part of the total amount of cottonseed treated for pink bollworm, but fumigation is a valuable alternative to heat treatment in newly discovered areas of infestation where heat-treating equipment is not available.

Fumigation likewise is used for treating commodities regulated by various State plant quarantines. Several States require the fumigation of white potatoes originating in California because of the potato tuberworm. Thousands of carloads of potatoes are fumigated with methyl bromide in compliance with those quarantines. California and Arizona require the fumigation of many plant-propagating materials as a condition of entry. When California removed restrictions on Texas citrus fruit because citrus canker was no longer found in Texas, many carloads of grapefruit were fumigated to destroy such surface insects as scales,to meet other California requirements. In 1940 or so, before the oriental fruit moth was found in Pacific Coast States, nursery-plant hosts that might carry overwintering larvae were allowed entry into Western States if they were fumigated before shipping; a large trade developed between midwestern nurseries and western fruit growers. When the insect was discovered on the west coast, fruit and fruit boxes were fumigated before moving from local quarantined areas to non-infested areas.

When Hawaii was quarantined because of the presence of the oriental fruit fly, two products were fumigated to permit movement to mainland markets. Millions of Vanda orchid flowers were fumigated in 1949 and 1950; later research established that the fruit fly could not finish its life cycle on the flowers even though eggs and young larvae were found on them. Then the restrictions were removed. Pineapples are shipped to mainland markets following fumigation to destroy eggs or larvae of the fruit fly attached to or embedded in the skin of the fruit.

RANDALL LATTA was leader from 1942 to 1951 of a project to develop treatments for plants and plant products regulated by plant quarantines. His staff works with plant quarantine units in the Bureau of Entomology and Plant Quarantine to develop proper dosage schedules and procedures for fumigating quarantined materials. In 1951 he became leader of the division of stored product insect investigations.

M. C. LANE is in charge of the truck crop and garden insect investigations laboratory at Walla Walla, Wash. He has been with the Bureau of Entomology and Plant Quarantine since 1917 and has been studying the life history and control of wireworms of the Pacific Northwest since 1920. Besides evolving several cultural control methods for wireworms on irrigated lands, he and his coworkers have evolved methods of ridding soil of wireworms through the use of fumigants and soil insecticides.