Special Difficulties

Leaf diseases are apparently subject to control by bordeaux mixture, but for the weevils, which damage the nuts previous to maturity, no satisfactory remedy has yet been discovered except the yarding of poultry in sufficient numbers to destroy the adult insects and their larvae when they reach the ground.

The most serious difficulty confronting the present or prospective chestnut-grower in North America is the chestnut-bark disease which, during the last decade, has worked havoc in the native chestnut forests throughout a region of country extending from central Connecticut through southeastern New York, New Jersey, and eastern Pennsylvania into northern Delaware, northeastern Maryland and northern Virginia. As this region contains most of the commercial plantings of improved chestnuts they have also suffered severely, especially since about 1908. The distribution of the native chestnut, together with the known distribution of the disease February 1, 1912, is shown on the accompanying map (Fig. 915), which was prepared by Metcalf to accompany a special report on the disease in response to a resolution of the United States Senate.

Fig. 915. Distribution of the chestnut blight.

This disease, caused by a parasitic fungus (Diaporthe or Endothia parasitica), attacks trees of all ages and kills by girdling at various points. It is known to attack all species of chestnut and chinquapin grown in this country, although some, at least, of the Japanese varieties, are practically resistant, so far as observed. A few cases of the disease have also been found on living trees of the chestnut oak in Pennsylvania, though with less evidence of destructive effect than on chestnut.

The disease is spread by the spores of the fungus, which are sticky, and are carried by rain, insects, and man, and probably by birds and small mammals. It is known to have been carried on nursery stock for long distances and is easily transported on newly cut timber and cordwood from which the bark has not been removed. Infection frequently occurs through wounds made by bark-borers.

Although first attracting attention in New York City in 1904, it appears certain that it had secured a firm foothold in southeastern New York, including Long Island and adjacent portions of Connecticut and New Jersey, prior to that time, there being some indication that it was introduced from Japan, although satisfactory evidence of this is still lacking. The presence of the disease in chestnut forests in China was discovered by Meyer in 1913, where, upon an unidentified species of chestnut, it is reported to be less virulent than in American chestnut forests.

For several years after publication of the cause of the disease by Murrill, in 1906, little effort was made in a systematic way to accomplish its control until 1911, when the legislature of Pennsylvania appropriated $275,000 for this purpose and inaugurated a state-wide, two-year campaign of eradication. The work is being done in cooperation with the Federal Department of Agriculture which, since 1907, has been investigating the disease with a view to developing effective methods of controlling it. Several other chestnut-producing states are also giving more or less attention to the problem. Up to the present time, systematic cutting out of infected trees coupled with destruction of their bark by fire has proved the only practicable control method. This is being vigorously applied in Pennsylvania and those portions of Maryland, West Virginia, and Virginia in which the disease has appeared.

In forests, the disease is exceedingly difficult to eradicate after it has once gained a foothold, owing to the minute examination of the entire tree which is required to locate infections in their early stages. In any district in which there is a general infection of the forests, the only practicable course is to clear off the timber while it is sufficiently sound to be merchantable.

The relative disease-resistance of the Japanese chestnuts, coupled with their precocity and productiveness, renders them now the most promising sorts for the American chestnut-grower. Planted in sections outside of the native range of the American chestnut, they may reasonably be expected to remain practically free from the disease, especially if care is exercised to prevent its introduction from infested regions on nursery stock or cions. The poor flavor and eating quality of most of these varieties is their worst fault, but in view of their wide range of variation in this respect, the problem of producing resistant varieties of good quality appears relatively simple. The few trees of Korean and Chinese chestnuts thus far grown in the eastern United States are apparently quite resistant to the disease and therefore of much interest to the tree breeder as parents of possible resistant forms. Systematic work on the breeding of resistant varieties is being prosecuted in the Bureau of Plant Industry.

Varieties Of Chestnuts

The varieties of the three species, although possessing many points in common, differ sufficiently in important characteristics to justify separate grouping for cultural discussion. As chestnut-culture is new in this country, it seems best to append descriptions of all the varieties which are in the American trade. For fuller discussion of cultivated chestnuts, see Nut Culture in the United States (Bull. Div. of Pomology, U. S. Dept. of Agric), from which Fig. 913 is adapted; Nut Culturist, A. S. Fuller, 1896; European and Japanese Chestnuts in Eastern United States, G. Harold Powell (Bull. Del. Exp. Station), 1898; Nut Culture for Profit, Jno. R. Parry, 1897.

American Group

Although the wild nuts exhibit wide variations in size, form, quality, productiveness, and season of ripening, but few varieties have been dignified by names and propagated. Solitary trees are frequently sterile, although producing both staminate and pistillate flowers, apparently requiring cross-fertilization to insure fruitful-ness. This is especially true of planted trees of this species on the Pacific slope, where productive trees are reported to be rare. The susceptibility of the species to injury by leaf diseases, as pointed out by Powell, and the injury to nuts by larvae of weevils, are drawbacks to its extensive culture.

The following varieties are propagated to some extent:

Dulaney

Bowling Green, Ky. Large, and of fine quality. Original tree productive, though isolated.

Griffin

Griffin, Ga. A large, very downy nut, of good quality.

Hathaway

Little Prairie Ronde, Mich. A large, light-colored, sweet nut, annually productive, frequently having five to seven nuts to the bur.

Ketcham

Mountainville, N. Y. Above medium in size, oblong, tomentose, sweet. Tree productive and vigorous in heavy sod at fifty years of age.

Murrell

Coleman's Falls, Va. A large, high-flavored nut, bearing three nuts to the bur.