Infestations of root-lesion nematodes—Pratylenchus vulnus—occur in all important walnut growing areas in California and high population densities cause a disease of economic importance. The disease is characterized by stunting, die-back, and chlorosis in the tops of the trees; by yield reduction; and by root symptoms consisting of black lesions, longitudinal cracking, and even death of entire roots. The disease has been induced experimentally by adding a suspension of the root-lesion nematodes to California black walnut seedlings.

Fred M. Charles, Farm Advisor, San Joaquin County, University of California, participated in this work.