Early crops of potatoes are subject to severe injury because they make the major part of their growth in the spring and early summer during the seasonal period when favorable temperature conditions for psyllid development normally prevail. Temperatures favorable to potatoes are likewise favorable to psyllid development. By the time that high temperatures occur in July the fully grown plants of the early potato crops are large enough to afford considerable shade and thus to protect the psyllids from temperatures above 70 . The later potatoes are planted in the season the less injury they suffer from psyllid infestation. In areas above 6,000 feet elevation the temperatures are low enough so that psyllid infestation can develop uninterruptedly throughout the growing season.

CONTROL can be achieved with chemicals if they are applied properly. A dust containing 5 percent of DDT in sulfur applied at the rate of 25 to 35 pounds per acre, or 2 pounds of 50 percent DDT in 100 gallons of water applied as a spray at the rate of 100 to 125 gallons per acre, is effective. Because the nymphs inhabit the under sides of the potato or tomato leaves, those parts must be covered thoroughly with the insecticide the duster or sprayer nozzles should be directed upward at a 45 angle from near the ground level and from each side of each row of the plants. On sprayers, a third nozzle should be directed downward on the center of each row of plants; a pressure of 350 pounds or more is necessary to force the spray into the foliage and attain a thorough covering of the leaves.

The first application should be made when the plants are about 6 inches high, except that on early potatoes the first application should be made when the plants are 3 or 4 inches high. When the infestation is light (3 or 4 psyllid adults in 100 sweeps of a standard insect net 15 inches in diameter) two or three applications at intervals of 10 or 14 days will be enough to obtain control. In epidemic years five applications at intervals of 10 or 14 days are needed. In years of heavy infestations it will be necessary also to continue insecticide applications after the vines have grown so large that no open spaces are left between the rows. This may be accomplished, without much injury to the plants, by the use of vine lifters on the spray or dust equipment.

The control of psyllids can be materially aided by the elimination of the spring host plants in both the northern potato and tomato areas. It is impractical to control wild Lycium in the southern breeding areas, since it is so abundant and widespread. But cultivated Lycium in the northern potato areas, if removed, would eliminate it as a plant on which psyllids collect and breed before the potato crops are growing. It can be easily killed with a herbicide containing 2,4-D. It is hard to kill by grubbing because new plants appear from any roots remaining in the soil.

Potato sprouts in cull piles are also a source of spring breeding of the potato psyllid before potato or tomato crops are growing. These potatoes sprout early and produce a dense growth where the psyllid is protected from adverse weather conditions. The plants developing from the sprouts die in July because of the lack of moisture and plant food. The psyllids then are forced to move to other hosts, particularly early potato crops. The menace caused by the growth of the potato sprouts can easily be prevented by spreading the tubers when they are dumped, so that the piles are not more than one tuber deep. Killing the growing sprouts with chemicals or plant-growth regulators is too expensive and slow to be of much benefit in preventing the spring breeding of psyllids.

Late planting of potatoes, where practicable, will avoid serious injury by the potato psyllid only 30 to 40 percent as many adults of the psyllid are found on potatoes planted after June 10 in western Nebraska as on those planted before May 20. Parasites and predators have some effect in keeping psyllids in check. The hymenopterous parasite, Tetrastichus triozae, has been found parasitizing many psyllid nymphs, in some seasons, particularly in the fall of the year, but their build-up in numbers is too late in the season to be of much benefit in controlling the psyllid. Another hymenopterous parasite, Metaphycus psyllidis, is reported to be effective in keeping psyllids in check in southern California. The larvae and adults of the convergent lady beetle and closely related species are predators on psyllid nymphs. The larvae of several species of Chrysopa are predaceous on the psyllid adults and nymphs. The big-eyed bug, Geocoris decorates, as well as Nabis ferus, are also predators of psyllid adults and nymphs.

R. L. WALLIS is an entomologist in the division of truck crop and garden insect investigations, Bureau of Entomology and Plant Quarantine. He was graduated from the Colorado State College of Agriculture in 1927 and has been in the Bureau since 1928. He has worked on the gypsy moth in New England, bean insects in New Mexico and Colorado, and potato insects in Colorado, Wyoming, and Nebraska.

Adult, pupa, and larva of the convergent lady beetle.