A method of determining the weevil infestation is:

Sweep the field soon after the first blossoms have appeared and before dusts have been applied. Go into the field in several places on each of the four sides, or, if the field is irregular in shape, sweep at intervals around it. Each stroke across the upper part of the vines is considered a sweep. Hold the net at such an angle that weevils knocked off the vines will fall into it. Take a step or two between each sweep. Make two or more 25-sweep collections at each place swept and count the weevils in each collection. Work toward the center of the field until no more weevils are found. In a field of seed peas, sweep toward the center of the field until the weevil population drops below the number for which it is considered profitable to dust, as we explain later. On a rough map of the field mark the locations where the weevils were collected. To keep track of the locations, it is helpful to step off the distance from the edge and sweep at 100-foot intervals. For instance, if weevils are found 200 feet from the edge of the field, walk another 100 feet and sweep again. If this method is followed, it is easy to mark the distance on the map.

Pay particular attention to the places most likely to be severely infested. Examine the edge nearest extensive timbered or brushy areas, ravines, and gullies running into the field; the vicinity of sheds or trees; and areas where the first peas blossomed, if the bloom is spotted. Check on the effect of the dusting operations in a similar manner 18 to 24 hours after dusting. If many weevils are found, it may be necessary to dust again within 3 or 4 days. We stress again that the green-pea field must be kept practically weevil-free, but in seed peas a light infestation is not so important. A more thorough check therefore is needed on the green-pea field, both before and after dusting.

GROUND AND AIRPLANE dusters have been used to apply insecticides. Power dusters should be provided with a box-type hood or a canvas trailer so as to confine the dust to the vines for a brief period before it is dissipated or the wind carries it away. The nozzles or hollow perforated boom for dust distribution should be so constructed as to distribute or blow the dust across the entire swath so that it can circulate freely through and around the vines before exposure to the effects of wind. The dusters are of many sizes and designs. Most have provision for telescoping, trailing, or dismounting the booms or hoods to facilitate movement from field to field. Some have special elevating devices for adjustment to the height of the vines. Those that cover swath widths greater than 30 or 40 feet (up to about 6o feet) have caster wheels at the ends of the booms or hoods to permit them to follow uneven field contours with efficiency and without damage to the equipment. Some are mounted in trucks. Others are on trailers that are pulled by tractors, jeeps, or horses. Sometimes the dusting machine is driven from a power takeoff by the tractor itself ; others are driven by separate engines. Providing they distribute the dust fairly uniformly at the required rates, all have been reasonably satisfactory.

Dust applications from the ground should not be made when winds exceed 10 or 12 miles an hour. Rotenone dust applications are most effective when temperatures reach or exceed 70 and should not be made at other times. That is because rotenone is effective only on immediate contact, and during cool weather weevils remain inactive and more or less concealed in places not reached by the dust.

Airplane dust applications have proved reasonably effective if properly made and supervised. Good applications to field margins are especially important, but that often is dangerous to do with airplanes and may not be too effective, especially if the fields are small, irregular, or obstructed by trees, power lines, or buildings. Ground equipment is recommended for such. In general, dust applications by airplane should be at rates about 50 percent greater than with ground equipment. Dust deposits from airplanes are largely concentrated in a narrow swath or zone, the effective width of which does not greatly exceed 25 to 30 feet. Airplane applications are also much more limited by wind than are ground applications. Such applications are effective only when made under nearly windless conditions where velocities do not exceed 2 or 3 miles an hour.

One of the greatest advantages of aerial application is the absence of crop damage by the equipment itself. With truck or tractor drawn ground dusters covering a swath width of 30 feet, the damage may amount to as much as 3 or 4 percent of the value of the crop in the part of the field actually treated. Light equipment and the use of dusters covering greater swath widths would substantially reduce the injury.

T. A. BRINDLEY, entomologist in the Bureau of Entomology and Plant Quarantine, devoted 20 years to a study of the biology, ecology, natural enemies, and control of the pea weevil and other insects affecting peas in the Pacific Northwest and in adjacent regions. He is a graduate of Iowa State College and pursued graduate studies there. Since 1950 Dr. Brindley has been coordinator of research in cooperative investigations in Iowa on the European corn borer between the Bureau of Entomology and Plant Quarantine and the Iowa Agricultural Experiment Station.

JOSEPH C. CHAMBERLIN, entomologist for more than 20 years in the Bureau of Entomology and Plant Quarantine, has done research on several of the more important insects affecting truck crops, including the pea weevil, pea aphid, and beet leafhopper in the Western States. He investigated the insects of Alaska in 1943-45. During recent years Dr. Chamberlin has worked with agricultural engineers to develop and improve aircraft for the application of insecticides to peas and other crops. Dr. Chamberlin holds degrees from Stanford University.