Fertilization increases Hylobius abietis L. damage in Pinus pinaster Ait. seedlings

Maritime pine (Pinus pinaster Ait.) is the most important forest tree species in Galicia (NW Spain), and the pine weevil (Hylobius abietis L.) can be a serious problem to its regeneration. Fertilization is a commonly recommended silvicultural tool for P. pinaster, especially in second rotation reforestations where large amounts of nutrients may be extracted through harvesting. But increased nutrient availability could promote undesired side-effect on host resistance and pest damage. We studied the effect of fertilization on pine growth and weevil damage during two growth periods after planting in a P. pinaster progeny×fertilization trial with nine fertilization treatments. Both factors, fertilization and family, had a strong and significant effect on growth and pine weevil damage. The damage by the pine weevil was greater in fertilized plants (debarked area score up to 2.9-fold greater) than in the unfertilized control, inducing a 3.7-fold greater leader loss in the former. The damage was lower when calcium phosphate was absent than when it was present, averaging about 2- and 2.7-fold above the unfertilized control, respectively. In spite of the attack, 1 year after planting, fertilization significantly increased diameter and height in plants that were able to maintain the leaders alive, averaging about 1.2-fold above the control. But when the height of the whole plantation was considered (actual height), fertilized plants did not differ from unfertilized ones. Moreover, the attack of H. abietis during the first growing period affected subsequent growth, resulting in no significant effect of fertilization on growth at the end of the second growing period. Attack by H. abietis caused the loss of the growth benefits promoted by the fertilization input.