We’ve talked about how to approach the falling leaves in your landscape, but what about the falling needles from evergreens, such as pines. As some evergreens are dropping their needles, when is it typical needle drop and when is it cause for concern? Let’s talk about that.

During the growing season, pines grow outward from the tips of their branches, producing new needles as they grow. As this growth continues, the older needles toward the center of the tree get shaded. In the shade, these older needles eventually turn brown and drop off.

You’ll first notice this as the inner needles begin to turn brown. If you are unaware of this yearly event, this might cause some concern on your part, but a typical pine tree can lose up to 1/3 of its needs each year. This is normal development in that tree. So, if your pine tree has browning needles toward the center of the tree, this is no cause for concern. These pine needles make a great mulch for your garden.

However, if your pine tree has browning needles at the edges of the branches, this could indicate the presence of what is known as pine wilt disease.

Pine wilt disease is a pretty common disease of pine trees, and it spreads. This particular disease is caused by a roundworm known as the pinewood nematode. These microscopic roundworms feed on the tree’s xylem (water conducting cells). Over time, their feeding takes it’s toll as they destroy the pines ability to draw up water, which leads to what seems like a pretty quick death of the tree.

During this decline, the pines typically also play host to something known as blue-stain fungi. Even after the trees falls victim to the nematode damage, the nematodes can still continue to feed on the blue-stain fungi. In fact, if you cut down a dead pine tree and find areas of the wood that appear to be stained blue, that would indicate the presence of this blue-stained fungi.

You may ask, how to these nematodes move from tree to tree if they are microscopic and live primarily in the tree? Well, they get a little help from the pine sawyer beetle.

Pine sawyer beetles like to lay their eggs in dead or declining pine trees. When paying their eggs, the beetle chews a hole in the bark and deposits their eggs inside that hole.

When the eggs hatch, the larvae feed on the inside of the tree, eventually making their way back to the surface to emerge as adult pine sawyer beetles. When dining on the inside of the tree, they come in contact with the nematode, which hitches a ride in the respiratory opening of the adult beetles. Then as that beetle moves from tree to tree, they are inadvertently, helping the nematode move as well.

If you have a pine tree that has browning needles at the ends of the branches, you can send a photo to our Diagnostic Center for confirmation of the diagnosis. At this point there is typically not much hope for your tree, but we love our trees so you still may want to contact an arborist to see. The bottom line is, don’t delay. Since your tree is infected, you’ll want to get it out or your yard as soon as possible. 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: Ryan Armbrust, Kansas Forest Service, Bugwood.org