S. H. Graham of Ithaca, N. Y. says: "The Ohio is commonly regarded as hard to hull. With a chained tire husker it hulls as well as any." He rates it for hardiness and a percentage of 90 to 100 for filled nuts, while Thomas yields only 0 to 90%.
Seasonal Zones Compiled from the U.S. Department of Agriculture Records, Based on the Average Date of the Last Killing Frost in Spring
Juglone—The Active Agent in Walnut Toxicity
By George A. Gries, Connecticut Agricultural Experiment Station
The problem of walnut toxicity dates back at least to the writings of Pliny. In his "Natural History," this Roman philosopher stated that "the shadow of walnut trees is poison to all plants within its compass" and that it kills whatever it touches.
The first rebuttal to the existence of such a toxicity was forwarded by Evelyn in the 17th century. This author discussed the high regard in which walnuts were held in Burgundy as field trees. The roots of these trees were below the plow sole and thus did not affect either cultivation nor the growth, of grasses and cereals beneath them.
The pros and cons of the problem have been reviewed several times in the recent proceedings of the Northern Nut Growers Association. (Greene, 1930; MacDaniels and Muenscher, 1942; Brown, 1943.) That the roots of walnut trees are toxic to the roots of certain crop plants in direct contact with them is widely accepted. In nature this toxicity seems to be limited to plants with tap root systems such as tomato and alfalfa (Davis, 1923) and those with other types of deep root systems such as apple trees (Schneiderhan, 1927), rhododendrons (Pirone, 1938), and privet. This toxicity is exhibited only when there is a direct contact between the roots of the two plants involved. (Jones, 1903; Massey, 1925). That the wilting observed under walnuts is due to a toxic product from the bark of the walnut, and does not result from a lack of water, is substantiated by the fact that the vascular or water conducting system is discolored for several inches above the point of contact with the walnut root. This symptom is very similar to that produced by vascular disease fungi. No such discoloration results from wilting due to competition for water. This symptom of toxicity has been overlooked by many workers in the field.