White pine cone crop and insect pests therein Would you believe our luck? We are barely into the State's White Pine Initiative and this year we have an excellent crop of white pine cones to supply the seed for our restoration efforts. A word to the wise for the many hundreds of people around the state who will be collecting cones this fall: watch out for cone pests. There are two cone-boring insects which can destroy part or all of the cone crop during the spring and early summer. You may want to do a late summer reconnaissance of your white pine stands prior to the fall cone collection. Fortunately, bug-infested cones are easy to distinguish from healthy, green cones.
Cone beetles and borers are capable of attacking and killing 100% of the cones in a stand or plantation. That only happens during the second year of two consecutive bumper crops. In an average year, it's more likely that these insects destroy to ½ of the cone crop. Even then there are still plenty of healthy cones to gather which contain good seed.
Not much work has been done in predicting insect predation of white pine cones. Here's what we do know. If you are doing a recon survey in July or August, look at the cones in the tree crowns and the fallen cones on the ground. The major pest to check for is white pine cone beetle, Conophthorous coniperda. When beetles are present, you'll be able to see dead, brown cones in the tree crowns and find brown, shriveled cones on the ground with a large pitch mass at the stem end. Female beetles sever the conductive tissues at the cone base, killing the cone whether or not a brood is produced. Resiny pitch masses are present at the entrance hole in the cone.
Infested cones turn brown, shrivel and drop to the ground during the summer. Infested cones will range in length from ½ inch to six inches long. Larvae or pupae may be found inside the cones. So if there seems to be abundant, green and growing cones up in the tree crown in July or August, chances are that beetles are not a problem.
White pine cone borer, Eucosma tocullionana, is a pest of secondary importance. Attacked cones are peppered with small holes and covered with patches of extruded frass. With this insect, cones on the trees may remain green and continue to grow for some time before drying and falling to the ground. In late summer, look for green and drying or brown and shriveling cones on the ground with one to several holes in them. Frass may be loosely webbed on them. Inside, the cone is tightly packed with a mixture of frass and resin. Again, if there seems to be abundant, green and growing cones in the trees in July or August, chances are that borers are not a problem.