Cottonwood leaf beetle (Coleoptera: Chrysomelidae) defoliation impact on Populus growth and above‐ground volume in a short‐rotation woody crop plantation

Abstract

Abstract The impact of cottonwood leaf beetle Chrysomela scripta F. defoliation on four plantation‐grown Populus clones was examined over three growing seasons. We used a split‐plot design with two treatments: protected (by insecticides) and an unprotected control. Tree height and diameter at 1 m were measured annually and above‐ground volume was calculated. Protected trees of most clones had grown over 2 m taller after three growing seasons. Diameter differences ranged from over 1–4 cm larger on protected trees. Insecticide protection increased above‐ground volume over 20 dm 3 in one clone, and at least 4 dm 3 in all others. Chrysomela scripta defoliation resulted in a 50–73% loss of above‐ground volume. Defoliation also resulted in increased lateral branching and forked terminals on unprotected trees. Defoliation impact varied among clone. The pure Populus deltoides clone 91 × 04‐03 showed the greatest growth response to chemical protection, whereas clone NM2 ( P. nigra × P. maximowiczii ) responded the least. Pest control is a key issue in short‐rotation plantation management. Until adequate pest‐resistant clones can be developed and natural enemy complexes better understood, chemical (biorational and organic) and cultural control may be used to reduce impacts of herbivorous pests.