Of the numerous foreign plant diseases which have gained entrance into this country, none has been more destructive than the chestnut blight, a fungous disease from Asia. In the last 25 years millions of acres of chestnut growth have been killed by the blight and the remaining American chestnuts in the East face certain destruction.

The chestnut-orchard industry of the New England and the Middle Atlantic States has been practically destroyed by the blight and there remain only rare trees of the American and European chestnuts or their hybrids and a small percentage of the more resistant Japanese chestnuts. Unfortunately the killing of the chestnut forest growth and orchards does not result in the self-extermination of the disease, as many of the roots of the killed chestnuts remain alive and send up sprouts which continue to spread the disease for many years. Consequently chestnut orchardists in the eastern half of this country can expect the blight to be an important factor, though losses from this diseases may be insignificant in localities where chestnut and chinquapin are not native.

Fig. 41.—A view of an orchard of hairy Chinese chestnuts planted by Doctor Van Fleet at Bell, Md. This species is being crossed with other species of chestnut. Many of the trees in this orchard have never had deep cankers which justified treatment, although the blight has been present in the orchard for the last 12 years

Experience in the department chestnut orchard at Bell, Md., indicates that in orchard practice the blight can be controlled on various strains of the hairy Chinese chestnut, Castanea mollissima, (fig. 41) at a reasonable cost. A simple treatment which has given satisfactory results with this species consists of cutting out every spring the trunk infections which reach into the cambium region and painting the cuts. The majority of the trees do not require the removal of infections every year, while some few trees frequently have deep cankers. In orchards where the blight is being eradicated, much more frequent, careful, and drastic treatment is required. It is important-in both the control and the eradication of the blight to keep the trees in vigorous condition. Although the blight can be controlled on the hairy Chinese chestnut, other factors such as the sale price of the nuts and the chestnut weevils, for which there is no satisfactory control at present, must be considered by the prospective orchardist.

Successful inoculations on varieties and species of chinquapins from different parts of the Gulf States and Arkansas show that the blight will eventually spread over the chinquapin area of the South. These shrubs will be a source of infection for orchards considerably outside the range of native American chestnut. As the chestnut blight is carried for long distances in various ways, there is no assurance that even the chestnut orchards of the Pacific coast will remain free from the disease. Orchardists and inspectors in that region should be on the watch for the blight, as young infections can be easily and completely eradicated, whereas older ones can be eradicated only with much greater difficulty.

The planted American chestnuts of the Northeast have largely disappeared, and those of the southern Appalachians and the Ohio Valley are doomed. Owners who are dependent upon these trees for shade should take immediate steps to plant resistant chestnuts or other kinds of shade trees to replace the native chestnuts when they die. Many strains of the Japanese and hairy Chinese chestnuts are sufficiently resistant to the blight to be grown as shade trees with very little treatment, whereas others are rather susceptible and require considerable treatment. The natural beauty of these trees, together with their production of edible nuts, makes them very desirable for planting in many situations. A few trees of the hairy Chinese chestnut will supply the farmer’s family with sweet nuts.

Most of the chestnut forest growth north of Virginia and east of the Allegheny River has been killed by the blight, and that of the southern Appalachians and Ohio Valley will be destroyed in the near future. As shown by Figure 42, the blight is now present throughout most of the range of the commercial chestnut. It is spreading more rapidly in the South than it did in the North, and already over one-fifth of the chestnut stands of the southern Appalachians are 80 per cent or more infected. Forecasts based upon the present distribution of the disease and its past rate of spread indicate that the major part of the remaining chestnut trees will be infected or killed by 1930. As the distribution and spread of the blight are somewhat irregular, each owner must watch his stand in order to determine the amount of infection in it.

Fig. 42.—Map showing distribution of the chestnut blight. In the eastern part of the heavily infected zone nearly all of the trees are dead, while on the western edge of this zone most of the trees though infected are alive. In the zone shown as less than 80 per cent infected, the percentage of infected trees ranges from less than 1 to 80.

Owners should make plans to utilize their chestnut poles before they are killed by blight, because killed poles will usually not be accepted by purchasers. Very severe financial losses have been suffered by many owners of standing poles, who failed to cut them before they were killed. Chestnut trees suitable for lumber should preferably be cut before they are killed, although such trees are not so much reduced in value as dead poles. To a limited extent chestnut which has been dead for many years has been utilized for making tannin extract, but the yield of extract from a given area is much reduced by the loss of sapwood and partial decay of the heartwood.

The future of the American chestnut as a source of tanning supplies is not promising. In regions where the blight has been present for many years some trees, which are much more resistant to the disease than the general average, have been located, but still more resistant trees must be found before it will be possible to recommend their planting.

The hairy Chinese chestnut, however, has possibilities as a source of tannin because of its resistance to blight and its high tannin content. Analyses of this species made by the Bureau of Chemistry and chestnut-extract companies show that its tannin content is higher than that of the American chestnut. However, the growth of this tree in China and in a few plantations in this country indicates that it is not so good a forest tree as the American chestnut.

Although America produces an excess of many farm products, it at present imports annually approximately 25,000,000 pounds of chestnuts as the domestic production from chestnut orchards is very small. This country also imports about one-half of the vegetable tannin supplies used in making leather, and with the passing of the American chestnut, whose wood yields approximately one-half of our domestic production of tanning materials, the United States will probably be dependent upon foreign countries for 75 per cent of its vegetable tanning supplies. In France the growers of chestnut not only receive a material income from the nuts, but also sell the mature trees and the trees removed in thinning to the tanning-extract companies. Such a combination may in the future prove profitable in this country since the hairy Chinese chestnut, which is not so prolific in nut production as the European chestnut, has a higher tannin content.