I 



October, 1929] 



WHITE PINE WEEVIL 



INDIRECT CONTROL METHODS 



27 



Silvicultural Control 



Silvicultural control may be brought about (1) by planting white pine 

 in mixed stands with hardwoods or other species of conifers; (2) by plant- 

 ing white pine densely. 



In planting white pine in mixed stands the principle involved is to 

 shade the trees sufficiently to reduce weevil attack and at the same time 

 not interfere with the growth of the white pine. The fact that the wee- 

 \il is a sun-loving insect makes some measure of control by this method 

 possible. The hardwoods or conifers used in the mixture should slightly 

 overtop the white pine during the most susceptible period to weevil at- 

 tack, that is, -Qntil the trees are about 20 feet high. If this practice is 

 followed care must be taken not to let the shade trees overtop the white 

 pine to such an extent that growth of the latter is retarded and the trees 

 become dwarfed and weakened from competition. Definite schemes of 

 white pine and hardwood mixtures cannot be suggested since each plan- 

 tation will present its own problem. 



At best this method is not easily planned, since it is difficult to regu- 

 late the proper amount of hardwood shade for the pine. In New Hamp- 

 shire the prevalence of the gipsy moth, Porthetria dispar, L., should also 

 be considered. Caterpillars of the gipsy moth in the third or later in- 

 stars will migrate to white pine and feed on it. 



Dense planting of pine is perhaps the most satisfactoiy method of 

 control. When white pine is closely planted the trees attacked by the 

 weevil are better able to recover from injurj' because the competition 

 for light and space stimulates them to grow straighter. The actual per- 

 centage of infestation per tree is reduced. In widely spaced stands the 

 trees tend to become bushy, forked, and crooked and are known as "pas- 

 ture" or ''cabbage" pines for this reason. Volunteer seedings of pine, 

 commonly found in New Hampshire, can be made promising plantations 

 by planting additional pines so that the density appro.ximates 1800 trees 

 to the acre. In connection with this method it is advisable to remove 

 the infested leaders in the manner previously described in order further 

 to reduce the infestation. 



Table VII. — Effects of Spacing 



