The most common type of sawfly to attack pine trees is the European pine sawfly. This insect prefers to feed on tabletop pines and Mugo pines, but will also attack Scotch pine, red pine, Japanese pine and Jack pine. Pine sawflies are wasp-like insects, but it is their larval form that is responsible for the damage to pine trees. The caterpillars are green in color and are 1 inch in length at maturity. The Southern pine beetle is often seen on dying pine trees, but it can infest healthy pines when they multiply and increase their population. The adult Southern pine beetle is most active when temperatures exceed 58 degrees Fahrenheit.
Pine trees are often found in home landscape designs and are often used as specimen trees. While pine trees are generally healthy, they are susceptible to infestations of insects that can damage the tree and its needles through feeding. Two common pests of pine trees are the European pine sawfly and the Southern pine beetle.
European pine sawfly larvae feed on the surfaces of older pine needles, causing the needles to look straw-like, turn brown and wilt. As the larvae mature and get larger, they feed in clusters to strip entire trees of their needles. Infested pine trees are often stunted, but they usually do not die from infestations because the larvae do not feed on new needles. Southern pine beetles first infest dying or weakened pine trees and move to healthy trees when their populations increase. These beetles tunnel inside the wood of the tree, placing their eggs in S-shaped galleries. Within three months, the pine tree is dead and the needles turn brown.
Inspect your pine trees in early April through May for signs of European pine sawfly egg laying. If you find eggs on the pine needles that have not hatched, remove them from the needle and destroy them. If colonies of larvae are feeding on your pine tree, you can remove them by clipping the infested branch from the tree or by knocking the larvae from the tree. Southern pine bark beetles are difficult to control because they enter the wood of the tree, where they are protected from insecticides. There are several predatory insects such as parasitic wasps that feed on bark beetles, keeping them under control.
Horticultural oils often work on sawfly larvae when applied while the larvae is small. General insecticide sprays will work on sawfly larvae and are often used if large numbers of trees are infested. Southern pine beetle infestations are hard to control with insecticides. Spraying the trees with insecticides as a preventative is the best way to control them. Trunk injections are often effective against bark beetles if they're applied before the damage to the internal wood is extensive.
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