Pine Wilt Disease is Fatal

Disease affects pine trees

By Bill Sevier Ask a Master Gardener | Posted:

Saturday, October 1, 2016 12:00 am

Q: My Austrian pine has started turning brown. It involves most of the tree. I don’t see anything abnormal other than brown needles. What should I do? Doris, Tulsa.

A: Unfortunately, the most common cause of pine trees turning brown and dying in the latter part of summer and fall is a condition called “Pine Wilt Disease.”

This condition is due to an infection of the tree’s circulation with a microscopic worm called a nematode. This infection is spread from tree to tree by an insect, the pine sawyer beetle. Because this infection is native born, native trees, such as loblollies, are less susceptible than the imported ones like the Austrian pines.

This beetle becomes infected by feeding on trees containing the nematode. The nematodes do not harm the beetle, but the infection is spread when it feeds on a healthy tree. The nematodes build up in the infected tree until they block all the circulation. The limbs become brittle and have little sap or resin. The needles stay fixed to the tree (as opposed to other conditions in which they drop) and the tree dies. Often there is an associated fungus that stains the wood of the tree blue. If a limb is cut, in addition to the lack of sap, bands of blue discoloration may be seen.

This is a fatal disease. The tree should promptly be removed and either chipped, burned or sent to the landfill. It is infectious, and if left in place, will infect a new crop of pine sawyer beetles the following spring that then spread the disease.

The other significant causes for browning of pine needles occur at certain times of the year. In spring, a disease called “Tip Blight” or Sphaeropsis or diplodia, appears as stunting and die-back of new needles (candles) on the tips of lower limbs. There may be dried resin and pepper-like specks on needles and cones. Also in spring, the pine tip moth may attack the new growth on tips of limbs, producing hollowed out limbs and webbing. These conditions involve only the tips, sparing the rest of the limb.

Another cause for brown needles is winter damage due to low temperatures and drying winds. This is often one-sided and is noted in early spring.

In late summer, another fungal disease called Dothistroma Needle Blight may appear, involving the tips of lower limbs. It may spread inward. The needles have discolored bands and die during the winter. The tree sheds them the following spring and summer.

Lastly, one of the more common causes, and one the Master Gardeners are often called about, is “normal needle drop.” Pines shed needles in the fall similarly to deciduous trees shedding their leaves. This involves the older needles, the ones closer to the trees trunk.

For the problems with pines other than pine wilt disease, there is treatment. Contact the Master Gardeners office for recommendations for control of the fungal and insect issues.

Garden tips

Begin preparing your outdoor plants for a move indoors. Move houseplants indoors when the outside and indoor temperatures are about the same. For plants in full sun, move to shade. Begin with light and then heavier shade over a week’s time to prepare the plant for the low light indoors. If you move the plant from full sun to a low light indoor situation, the plant may experience “shock,” lose leaves and perform poorly inside.

Inspect plants for insects and disease and treat accordingly. In many cases, a few insects can be controlled by hosing down the plant and removing them by hand. Another option is to use an insecticidal soap spray. This is effective and safe for you and your plant.

Also consider drenching the pot with 2-3 pot volumes of water to help remove insects and residual fertilizer salts.