Exploring Novel Management Methods for Beech Leaf Disease, an Emerging Threat to Forests and Landscapes

Abstract

Abstract Beech leaf disease, caused by the foliar nematode Litylenchus crenatae ssp. mccannii, deforms leaves and causes defoliation in beech (Fagus spp.). We explored management of this nematode, which threatens the health of shade-tree, ornamental, and forest beech. Field and laboratory evaluations over three years demonstrated that properly timed foliar applications of fluopyram reduced counts of live nematodes by > 90%. In vitro bioassay of fluopyram yielded an EC50 of 1.2 ppm. Similarly, oxamyl was effective when applied via trunk injection or as a soil drench to trees with < 20 cm (8 in) trunk diameter early in the season, but due to a short residual, failed to protect buds from becoming colonized in the late season (i.e. fall). High mammalian and environmental toxicity of oxamyl may limit interest in its use to injection capsules. Root flare injection or soil application of abamectin, acephate, emamectin benzoate, or potassium phosphite were ineffective in suppressing nematode populations or protecting foliage. Effective treatments cannot improve the aesthetics of trees during the current season but may protect the health of the trees by limiting the numbers of nematodes that infect buds and cause damage to foliage the following season. Species used in this study: American beech, Fagus grandifolia (Ehrh.); European beech, Fagus sylvatica (L.); North American beech leaf nematode, Litylenchus crenatae ssp. mccannii (Carta et al.). Chemicals used in this study: abamectin (Aracinate and Lucid), acephate (Lepitect), emamectin benzoate (Mectinite); fluopyram (Broadform, Indemnify, and Luna Experience), horticultural oil (RES Hort Oil), oxamyl (Return), potassium phosphite (Polyphosphite 30), tebuconazole (Torque).