Heavy, gusty, beating rains dislodge many aphids from the plants, kill them outright, or entangle them with mud. Such developments early in the summer delay the time when the aphids reach their greatest abundance. That can be a big factor in determining the maximum number of aphids that may develop on a potato plant and also the length of time during which the plant will be infested with large numbers of aphids. A delay in Maine in the time of development of large numbers of aphids on potatoes, especially during the time when the tubers are growing rapidly, can greatly influence the yields.

BEFORE the Second World War, some nicotine and rotenone were used on potatoes against aphids. Both were expensive.

The first use of DDT on potatoes in Maine and Washington gave promising results. In 1946 most of the potato acreage in Maine received 2 to 10 applications of fungicidal sprays containing DDT. In 1947 practically the entire potato acreage in the Yakima Valley, Wash., was dusted with DDT. The use of DDT or some other aphicide has since become standard practice. The number of applications to potatoes has increased each year, until in 1950 an average of eight was made in Maine and four in Washington.

The increased use of insecticides on potatoes in Maine has meant large increases in yields. In the 10 years before 1946, the average yield was 277 bushels an acre. In 1946 it was 355 bushels and in 1950, 480 bushels. These increases largely have been due to better control of aphids.

Ordinarily the insecticides are applied with ground machinery and in spray or dust form with or without fungicides, as conditions may require. In Maine both spraying and dusting are effective. In Washington dusting is preferred because it is faster.

EITHER EMULSIFIABLE DDT concentrates or DDT wettable powders can be used in preparing sprays for potatoes. For DDT concentrates, a sufficient amount of the material is mixed in 100 gallons of spray to provide a half pound of DDT in the spray mixture. For wettable DDT powders, enough of the powder is washed through a screen into the spray tank to provide 2 pounds of DDT in the spray mixture. DDT deteriorates rapidly in alkaline mixtures but may be used with bordeaux mixture if the spray is applied immediately after the DDT is added. DDT is compatible with neutral copper compounds, organic fungicides, and oil solvents. The sprays are applied at the rate of 125 gallons an acre.

In Maine the effectiveness of DDT dusts has been increased by the addition of a small amount of a relatively nonvolatile oil. Non-oiled dusts should contain 5 percent of DDT; if approximately 4 percent of oil is added during the mixing, the amount of DDT required may be reduced to 3 percent. A DDT-impregnated dust mixture is satisfactory when it contains 2 percent of DDT and 4 percent of oil. DDT may be included in non-oiled copper-lime dust mixtures only if the dusts are applied immediately after mixing. Dusts are applied at the rate of 30 to 35 pounds per acre depending upon the size of the potato plants.

PARATHION and some of the other organic phosphates are proving to be powerful aphid killers, but they must be handled and applied with great caution. Excellent control of the aphids can be obtained by applying sprays containing in each 100 gallons of the mixture as little as one-half pound of a 15 percent parathion wettable powder or one-half pint of a 25 percent parathion emulsifiable concentrate. The aphid-control value of some organic phosphates is reduced when put into an alkaline spray mixture such as bordeaux.

Trials conducted in Washington have shown that dusts containing 5 percent of DDT and at least 50 percent of dusting sulfur are superior to 5 percent of DDT dusts without sulfur against the green peach aphid. In 1950 and 1951 a dust containing 5 percent of DDT, 50 percent of sulfur, and 0.5 percent of parathion was more effective than a DDT-sulfur dust and is recommended for the control of aphids on potatoes.

The aphid killers are most effective when the potato foliage is completely covered by the spray or dust. For that, efficient, well-adjusted machinery is needed. In spraying, best coverage is obtained with a spray boom equipped with the dropped type of nozzles. In dusting, one or two nozzles should be directed on each row and set in such a way that the dust will be driven into the plants from the top or from each side of the row. A trailing apron, 6 to 15 feet long, of canvas or duck cloth, and attached to the duster boom, confines the dust about the plants momentarily and improves the coverage of the plants.

IT IS BEST to start the applications as soon as the potato plants appear above ground. In Maine applications should be made every week. In Washington applications seldom can be made more frequently than every 8 to 12 days because of conflicts with irrigation of the crop. The use of vine-lifter attachments enables one to continue applications without damage throughout the growing period.

Besides using aphid killers, it is well to kill the weed hosts that grow in crops and wasteland. Aphids do not carry leafroll and other virus diseases unless they feed on diseased plants. The use of the best seed potatoes available, early roguing out of all diseased plants, early harvesting of seed potatoes, and effective aphid control should prevent severe outbreaks of leaf roll in the future.

W. A. SHANDS, an entomologist of the Bureau of Entomology and Plant Quarantine since 1929, since 1940 has studied the seasonal movements and habits of aphids that attack potatoes in Maine and the development of control measures. Previously he engaged in investigations on the beet leafhopper in Utah, Colorado, and Arizona and tobacco insects in North Carolina and was assistant leader of the division of truck crop and garden insect investigations an Washington, D. C. He is a graduate of Clemson Agricultural College and did graduate work in the University of Minnesota.

B. J. LANDIS, entomologist of the Bureau of Entomology and Plant Quarantine since 1928, has conducted investigations on the habits and control of aphids, flea beetles, and other insects affecting potatoes in Washington since 1940. He also has studied the Mexican bean beetle and other insects affecting vegetables in Ohio and in Mexico, insects affecting raspberries and blackberries, and the European earwig. He is a graduate of Miami University. He did graduate work at Ohio State University.