pruning is to be favored and will pay well in developing straight post or pole timber. A second pruning will usually be required from 1 to 3 years after the first pruning. The character of growth will determine whether later pruning becomes necessary.
Overpruning should be avoided, as severe cutting almost stops the growth of the tree. The leaves are virtually the food factor of the tree. In them is manufactured all of the substance out of which wood is made. Pruning should be done in midsummer, as there is then the least opportunity for successful sprouting.
(9) Thin out the less vigorous trees in black locust stands (fig. 15). They are most susceptible to infestation and often become breeding trees for insects. The survival of larvae in the spring is least on the dominant and more vigorous trees and highest on stunted trees. Quite similarly, old, overmature locust trees are dangerous breeding places; therefore, if any occur near young stands they should be cut and used.
(10) No practicable method of direct control of the locust borer is known that can be applied to large-scale or forest plantations of black locust. However, treatment for killing or controlling the borer on individual trees of special value, such as those planted on lawns or streets, may be practicable. An effective method is to spray the trunks, especially the lower parts up to 8 feet in height, with crude orthodichlorobenzene solution. This should be prepared in the following proportion: 1 gallon of orthodichlorobenzene, 1 gallon of soft water, and 1 pound of fish-oil soap or common laundry soap. The soap is dissolved in boiling water and after the mixture has been well cooled, the orthodichlorobenzene is added, and the whole stirred well. To make up the spray solution, add about 4 parts of
