[Footnote 10: Gravatt, G. F., and Marvin E. Fowler. Diseases of chestnut trees and nuts. Northern Nut Growers Assoc. Rept. (1940) 31: 110-113. 1941.]
Phytophthora root disease, caused by _Phytophthora cinnamomi_, is treated briefly here, and interested nut growers can consult the detailed earlier article.[11] Briefly, this fungus is considered as introduced into this country over a hundred years ago. It killed the chestnut and chinkapin growth over large areas in the southern States. Asiatic chestnuts are highly resistant to this disease, and when grown on well-drained soils have not been damaged. Our test plantings of Chinese chestnuts growing in the same soils where susceptible trees of American and European chestnuts were killed, continue to make a vigorous growth. The European and American chestnuts and their hybrids growing in the western States are in danger from this fungus as it has now been reported in the West. This same fungus sometimes kills thousands of young nursery trees of the black walnut, but these epidemics are usually brought on by unusual weather conditions. Poor soil aeration, induced by excessive rainfall and poor drainage, makes ideal conditions for damage to the walnut and other hosts by _Phytophthora_. Even the very resistant Chinese chestnut roots are invaded by the fungus when the soil remains waterlogged for extended periods.
A systemic brooming disease, observed on planted walnuts as early as 1917, has been the subject of considerable discussion during recent years, because it has now spread widely into the native black walnut growth. In 1932 Waite published that he had been observing the disease for some 15 years but that "it was unknown on the black walnut in the wild in this country or on planted trees away from the Japanese walnut." The disease has continued to increase in prevalence in recent years and is now widely distributed in native black walnut growth in Tennessee, Virginia, District of Columbia, Maryland, Delaware, and New Jersey. This extensive spread into the native growth during the last 15 or 20 years and the fact that reports indicate that all of the early cases of the disease were found near nursery-grown trees offer some evidence that the disease is an importation from another area or continent into the eastern black walnut zone. From the literature and oral reports, it seems that the disease is now present also in North Carolina, West Virginia, Pennsylvania, New York, Ohio, and Michigan. Surveys probably would uncover the disease among native wild and planted walnuts in other States.