My pine tree has some needles that are turning brown. What could be wrong? SW

This time of year, we tend to get a variety of calls about pines or other evergreens with browning needles. Typically, this is normal needle drop, but browning needles can sometimes indicate a bigger problem.

Even though pines are called evergreens, they lose a certain percentage of needles each fall. In spring, pines generate new needles at the tips of their branches. These new needles last for more than one year. As the tree grows each year, the newest needles are at the tips of the branches while the older needles end up further back on the branch. Consequently, as these aging needles get shaded and become less active, they eventually turn brown and drop off. These dropped needles can be a good source of mulch for your garden.

A pine tree may lose up to 1/3 of their needles this natural way each season. Needle drop of this type should occur throughout the interior of the tree, not just in particular areas. Brown needles on only one side of the tree for example, might be the result of freeze damage from earlier this year or some other environmental damage.

However, if the needles are browning all over your tree and not dropping to the ground (key symptom), pine wilt disease is likely the problem. Pine wilt disease is caused by a microscopic roundworm called a pinewood nematode. Pinewood nematodes feed on the water-conducting (xylem) cells in pine trees. When feeding, they disrupt the flow of nutrients and water within the tree bringing about the eventual death of the tree. Typically, trees afflicted with this problem go from seemingly good health to brown and dead fairly quickly. As infected trees decline, they often also play host to blue-stain fungi. Nematodes can survive in dead trees by feeding on this blue-stain fungi.

An interesting aspect of this disease is that the nematodes don’t move from tree to tree by themselves. They hitch a ride on Pine Sawyer Beetles. Here’s how that happens.

Pine sawyer beetles chew a small hole in the bark of a declining or dead pine tree and lay their eggs. As the larvae feed, they eventually work their way back toward the surface of the tree. After pupating, the adult emerges by chewing its way out of the bark. While the pine sawyer beetle makes it’s exit, the pinewood nematodes move into the beetles’ respiratory openings. When the pine sawyer beetle moves to a new tree, the pinewood nematodes go with them, and the process starts all over again.

Once these trees are infected, there is no cure. Dead pines should be removed from the landscape since they will continue to be a host for both nematodes and pine sawyer beetles. Hopefully, your browning needles are the result of natural needle drop. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org.

 Photo: A. Steven Munson, USDA Forest Service, Bugwood.org