Walnuts for the Northeast

Abstract

The walnut has been held in high esteem since ancient times. The Romans considered it preeminent among nuts and gave it the name jovis glans (Jupiter's nut), from which the modem taxonomic name for the walnut genus, juglans, has been derived. Several species of walnuts are popular throughout the Western World today, both for their fine wood and flavorful nuts. Large commercial walnut industries exist in the Mediterranean region of Europe and on the west coast of the United States (primarily California, with 200,000 acres). Although walnuts are grown throughout much of this country, they have never been grown widely in the Northeast. Several types can be grown here, however, including the Persian walnut (juglans regia L.), the black walnut (J. nigra L./, the butter-nut (f. cinerea L.~, and the Asian walnuts (J. ailanthifolia Carr, j. mandshurica Maxim., and j. cathayensis Dode), all of which have nutritiou6, flavorful nuts. We will explore in the following the merits of these types and their cultivation in the northeastern United States and adjoining areas of Canada. Any talk of walnuts must begin by ad-dressing the toxic effect walnuts are said to exert on neighboring plants. Pliny the Elder, in the first century A.D., wrote, "the shadow Black walnuts / Juglans nigra/ ripening on the tree. Al Bussewitz photo. of walnut trees is poison to all plants within its compass...." While it is true that walnut species (and some hickories) produce a toxic chemical identified as juglone (5-hydroxy-l, 4-napthoquinone) the actual phytotoxic ef-fect varies considerably depending on / 1 ~ the different levels of tolerance among plants, (2) whether or not the roots of adjacent plants contact the walnut root, and (3) the amount of air present in the soil. Although the black walnut probably has the most notorious reputation for allelopathy (as destructive chemical interaction between plants is known), this phenomenon has been increas-ingly documented throughout the plant world, and it is worth noting that tall fescue grass (Festuca arundinacea Schreb.) exerts a similar deleterious effect on walnuts (Riet-veld 1981/. (. Toxic juglone is oxidized from hydroju-glone, a nontoxic substance found in all parts of the walnut plant. Oxidation of hydrojuglone occurs in the presence of air and during contact between walnut roots and the roots of other plants that contain oxidizing compounds. Hydrojuglone is highly reactive, however, and in the con-tinued presence of air quickly breaks down into harmless substances. Root-to-root