Because of scarcity of trees and long growing period required to get wood, walnut lumber is not in great demand as it used to be. More frequently grown in Europe for lumber. Walnuts grown in United States for nuts and ornament. Well-formed trees will yield lumber worth thousands of dollars. Disease overwinters in fallen leaves and reinfects new leaflets in mid May until mid June, often defoliating entire trees.
Many nuts are empty or contain blackened, shriveled kernels.
Bunch disease, the cause and means of spread are unknown, stunts growth of tree and lowers nut production. Most serious insect pests are walnut lace bug, curculios, walnut husk maggot, walnut caterpillar and fall webworm. Serious damage may also be caused by leaf-eating caterpillars, scales, aphids and twig girdlers. County agricultural agents should be consulted for measures to control these in a particular area. References Duke, J.A. 1978.