Juglone Inhibits Pine Growth Under Certain Moisture Regimes

Abstract

Black walnut (Juglans nigra L.) produces juglone (5‐OH‐1, 4‐napthoquinone), a phytotoxin that has allelopathic effects on certain plant species. Field studies were conducted in southwestern Ontario, Canada, in mixed plantations of red pine (Pinus resinosa Ait.), white pine (P. strobus L.) and walnut growing on the Brant‐Tuscola‐Colwood catena of fine sandy loam soils. On excessively drained Brant sites pine often suppressed the walnut while on imperfectly drained Tuscola and poorly drained Colwood sites, walnut suppressed or even killed the pine. In laboratory studies juglone and its inhibitory activity readily disappeared from Brant soil under a “dry moisture regime” but remained in Brant soil under a “wet moisture regime”. The field and laboratory studies suggest that edaphic conditions play an important role in the interactions between walnut and other species.