Resistance of Scotch Pine Varieties to Zimmerman Pine Moth (Lepidoptera: Pyralidae) and Its Impact on Sales in a Choose and Cut Christmas Tree Plantation

Nine varieties of Scotch pine, Pinus sylvestris, were assessed for their susceptibility to Zimmerman pine moth, Dioryctria zimmermani, in a choose and cut Christmas tree plantation. Trees were examined for wounds to estimate their susceptibility to this pest 7 years after planting in the field. Numbers of trees remaining after seasonal sales in years 7 and 8 were used to estimate marketability of each variety. Infestation rates varied significantly among varieties (11-75%). After sales, proportions of trees remaining also varied significantly among varieties (7-52%). Although Belgian trees were the most moth resistant, they were the least purchased by the public, probably owing to their yellow-colored foliage. Excluding the Belgian variety, proportions of infested trees were positively related to the number of trees remaining after two years of sales (F=12.7 df = 1,22, R2=0.37, P\u3c0.002). This linear relation suggested that in a population of 100 trees, three trees must be wounded to cause one not to be sold. This implies that appearance of advanced damage symptoms such as brown and broken branches have a greater negative impact on sales than the simple presence of wounds