The destruction by blight of the native stands of the American chestnut, and of the small eastern orchard industry based on European and American chestnuts and their hybrids is almost complete. Blight has been found in the planted European chestnut orchards of the Pacific Coast from time to time, but it has been kept under control by eradication. Chestnut trees or nuts from the eastern States, where blight is common, should not be shipped into the Rocky Mountain or Pacific Coast States.
Finding the Asiatic chestnuts resistant to the blight, the Division of Forest Pathology sent R. Kent Beattie to Asia to make selections of chestnuts for introduction into this country. Later Peter Liu, a Chinese collector who worked with Mr. Beattie, continued to select Chinese chestnuts for introduction. These introductions, together with the earlier ones made by the Division of Plant Exploration and Introduction, were grown at Chico, Calif., Savannah, Ga., and Bell, or Glenn Dale, Md. Altogether some 300,000 chestnut trees, of pure species and hybrids, were distributed to cooperators for forest and orchard plantings. (Fig. 1.) These constituted a fine lot of material from many parts of Asia as a basis for selecting the best ones for our use. Private nurseries and State game and forestry departments are now growing these chestnuts and the Division of Forest Pathology has discontinued general distribution of trees to cooperators.
Chinese chestnuts have proved to be the most valuable for forest, orchard and ornamental use. The Japanese chestnut is being discriminated against because of the poor quality of its nuts. Orchardists having mixed plantings containing Japanese chestnuts are advised to top work the trees or remove them, if the seed is to be used for plantings. In fact, for orchard plantings, nuts should be used only from the best individual trees of the Chinese chestnut.
The Chinese chestnut should be planted on sites with good air drainage as it is very susceptible to injury from early-fall or late-spring freezes. Many persons think their trees have been killed by the blight when the primary cause of the trouble was injury to the trunk by freezing followed by growth of the blight organism over the injured parts. This fungus may grow for many years in the outer layers of the bark without doing any material damage to the tree. An important factor in resistance of the Chinese chestnuts to the blight is to keep the trees growing vigorously. Avoid late growth in the fall as this favors fall freezing damage.
[Illustration: Figure 1.—F1 hybrids between the Chinese chestnut and the American chestnut.]
+Nut Spoilage+
In the Southern States one of the most serious problems with some selections of the Chinese chestnut is the spoilage of the nuts. Marvin E. Fowler made a study of this trouble at Savannah, Ga., and found that most of the trouble in that restricted area was caused by a Gleoesporium-like fungus that infects the nuts at the tip.[10] Because spraying experiments did not give control, the more susceptible trees have been removed. In most parts of the South, however, this fungus is not the primary cause of nut spoilage and the limited work so far carried out has not revealed the cause. Part of the trouble may be due to physiological break-down. As individual trees vary greatly in susceptibility to this deterioration of the nuts, orchardists are advised to top work or eliminate the more susceptible trees. Some people have believed that exposure of the nuts to the hot sun while in the bur or on the ground may cause damage. The market for Chinese chestnuts can be ruined by shipping nuts that are partly spoiled by the time they reach the consumer.
[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 of Chestnut+
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.