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

Abstract

1 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. 2 Protected trees of most clones had grown over 2 m taller after three growing seasons. Diameter differences ranged from over 1-4cm larger on protected trees. Insecticide protection increased above-ground volume over 20dm3 in one clone, and at least 4dm3 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. 3 Defoliation impact varied among clone. The pure Populus deltoides clone 91 x 04-03 showed the greatest growth response to chemical protection, whereas clone NM2 (P. nigra x P. maximowiczii) responded the least. 4 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.