As it’s getting colder and the leaves are starting to fall, it won’t be long before we start calls about brown needles on evergreens such as pines. We call them evergreens because the remain green throughout the year. However, even healthy evergreens, like pines drop some needles each year. Typically, this is not anything to be concerned about. Here’s why.

 During the year, pines grow from the tips of their branches, generating new needles as they grow. With this growth pattern, the newer needles will be at the tips of the branches while the older needles remain in place. As you can imagine, this new growth eventually shades the older needles. Without the sun, these older needles loose viability, gradually turning brown and dropping off. 

While this might sound like a minor thing, a typical pine tree can lose up to 1/3 of its needles in this way each year. If you are wondering what to do with all the dropping needles, they can be used as a great mulch in your garden, so that’s a plus.

When these trees are healthy, the browning needles will be found more toward the interior of the tree. However, if your pine has browning needles in the interior and the outer edges of the branches, this suggests the presence of a disease called pine wilt disease. 

Pine wilt disease is caused by a roundworm known as the pinewood nematode. While these little worms can do a lot of damage, you won’t be able to see them since they are microscopic. 

Once a pine tree becomes home to nematodes, they begin to feed on the tree’s xylem (the water conducting cells). Eventually, their feeding disrupts the flow of water and nutrients to the tree, causing the tree to die. Basically, you will probably be unaware of a nematode problem until the damage has been done. 

As pines begin to decline, they also can become host to a blue-stain fungi which continues to sustain the nematodes even after the tree has died. If you cut down a pine tree that has fallen victim to pine wilt disease, you’ll likely find some portions of the wood that have a blue tint. This is evidence of the blue-stain fungi. 

Nematodes are not able to move from tree to tree without some help, and they get that help from the pine sawyer beetle. Pine sawyer beetles like to lay their eggs in dead or declining pine trees. To accomplish this, they chew a hole in the bark and deposit their eggs inside that hole. Feeding beetle larvae, feed their way back to the surface of the tree and eventually emerge as an adult pine sawyer beetle. As they chew through the wood of the infected tree, the nematodes hitch a ride in the respiratory opening of the beetle. When the beetle moves to another tree, the nematodes emerge, and the process begins again. 

Once a tree is infected with nematodes, unfortunately there is no cure. Because of this, you should remove a dead pine tree as soon as possible to help minimize the ability of the nematodes to move from one tree to another. 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 - Ronald F. Billings, Texas A&M Forest Service , Bugwood.org