The small number of requests for information on insect pests of northern tree nuts received in the Bureau of Entomology and Plant Quarantine is a strong indication that such pests are of little concern to northern nut growers. This is fortunate, because intensive, all-season spray programs, such as are necessary to produce most other crops without serious losses due to insect injury, are laborious and expensive and not always as effective as desired. However, as your acreage is increased and as your trees become older and larger, insect problems are likely to increase in number and intensity and require more of your thought and attention.
A somewhat similar situation prevailed in the pecan industry at one time in the South. I well remember the statement of one of the larger pecan growers in Louisiana to the effect that all the pleasure of growing pecans would be gone the day he had to start spraying to control insects and diseases. Only a short time later it became necessary for him to initiate a regular spray program. He still took great pride in growing pecans, however. It is well, therefore, for you to watch your trees closely for insect damage and keep informed concerning the habits and control of the species that show up in your plantings or in those of your neighbors.
Because of the scattered nature of the northern nut industry, the small size of most plantings, and the more pressing demands for information on the control of pests of more intensively planted crops, it has not been possible for the Bureau of Entomology and Plant Quarantine to give attention to many of the pests of northern nuts. A great deal of work has been done on the pests of pecans in the South, and some work on those that attack filberts and chestnuts. In addition, some of the pests with which you are concerned, or others similar to them, are receiving attention in connection with studies of pests of tree fruits. The results of these studies will give you up-to-date information applicable to your particular problems.
The timely use of insecticides is the most effective means of combating most injurious insects, but if spraying is not possible, other methods can often be used to prevent or reduce damage. A great many new insecticides have become available during the last six or seven years. Work with them has resulted in the development of treatments effective against a number of pests for which there was formerly no known means of control and markedly more effective treatments for the control of others. It is my purpose to bring to you as much of this new information as is applicable to your problems.
Leaf-feeding Caterpillars
The fall webworm[3] and the walnut caterpillar[4] are the leaf-feeding caterpillars most commonly reported as attacking northern tree nuts.
Fall webworms[5] are the insects usually responsible for unsightly webs on or near the end of the branches of the trees during the summer and fall. They enlarge the webs as they need more leaves. When nearly full grown they scatter to complete their feeding. The full-grown caterpillars are a little more than an inch in length and are covered with long black and white hairs. They spend the winter in cocoons in trash on the ground or just below the surface of the soil. There are two broods a year in many areas, the second usually being the more numerous.
Control can be obtained by applying a spray containing 3 pounds of lead arsenate with an equal quantity of hydrated lime (to prevent possible injury to the foliage), 2 pounds of 50-percent DDT wettable powder, or 2 pounds of 15-percent parathion wettable powder per 100 gallons of water. Apply the spray when the caterpillars are still small. Follow the precautions furnished with each package. Parathion is a particularly dangerous material to use. If you are not equipped to spray or have only a few trees, you can control this insect by removing the webs from the trees with a long-handled pruner or a long bamboo pole with a hook at the end.
The walnut caterpillar feeds in groups, or colonies, and commonly eats all the leaves on small trees or on certain limbs on large trees. The winter is spent in cocoons in the ground. The moths appear late in the spring or early in the summer and lay masses of eggs on the underside of the leaves. From time to time as they grow, the stout, black caterpillars go down to a large limb or to the trunk of the tree to molt, or shed their skins. After molting they return toward the ends of the branches and resume their feeding.
This insect can be controlled with the same spray treatments that are recommended for the fall webworm, and also by crushing or burning the caterpillars when they are clustered on the lower limbs or tree trunks.