Interactions of Water Stress, Honeylocust Spider Mites (Acari: Tetranychidae), Early Leaf Abscission, and Growth of Gleditsia triacanthos

Sixty honeylocust trees, Gleditsia triacanthos variety inermis Skyline', were grown for 2 yr in containers. Irrigation and infestation with the honeylocust spider mite, Platytetranychus multidigitali (Ewing) were manipulated in July and August of 1991 and 1992 to determine the impact of water stress and spider mite infestation on tree health. Water stress had no impact on spider mite populations in this study. Drought-stressed trees assimilated CO 2 at half the rate of trees receiving adequate water; but after 2 yr, the trunk diameter of water-stressed trees was only 12% less than that of adequately watered trees. Spider mite infestation did not affect tree growth. Water stress and mite infestation caused early leaf abscission. By 17 September 1991, healthy trees with no stresses had lost 30% of their leaves, mite infested trees 50%, water stressed trees 52%, and trees that were water stressed and infested with mites had lost 69% of their leaves. Similar results were obtained in 1992. No predator mites were found in either year.