Pine Diseases: How Do Austrian Infections Affect White Pines?

Austrian pines are susceptible to several diseases, including Diplodia (Sphaeropsis) tip blight, pine wilt nematode, and Zimmerman pine moth. These diseases can cause the needles to turn brown and fall off, and in severe cases, lead to tree death. While rare, these diseases can sometimes affect native white pines. Pine wilt, for example, is caused by the pinewood nematode, a microscopic worm that clogs the water-conducting vessels of a tree, resulting in needle browning. Diplodia tip blight, caused by the Sphaeropsis sapinea fungus, also causes needle browning and tree disfigurement. Therefore, it is important to be vigilant about the health of Austrian pines and take preventive measures to avoid the spread of these diseases to white pines.

Diplodia (Sphaeropsis) Tip Blight

The Diplodia fungus affects the current year's shoots and sometimes branches, disfiguring or even killing them. The needles at the tips of branches are killed, with symptoms often starting on the lower half of the tree and progressing upwards. When the new needles (candles) are expanding, they become stunted, turn yellow, and then tan or brown. Resin droplets from cankers are often seen on the dead shoots, and during summer and fall, black fungal fruiting bodies will appear at the base of the needle under the fascicle (sheath). As lateral shoots are killed, whole branches may die back to the trunk, and the tree becomes disfigured. This disease can also cause perennial cankers that result in branch death.

The Diplodia fungus overwinters as fruiting bodies in infected shoots, bark, and seed cones. In wet weather, tiny spores erupt from them and infect the new needles (candles) as they expand in the spring. After the needles have fully expanded, the shoot can no longer be infected by the fungus. The spores are spread by wind and rain, infecting susceptible plant parts by penetrating wounds or stomata (breathing pores). Once the fungus has penetrated the plant, it spreads rapidly through the needles, then to the stem and nearby needles, which begin to die several weeks after infection.

To prevent infection, it is important to maintain tree health, as the disease is more severe in trees under stress. Proper watering, mulching, and avoiding pruning during late spring to early summer when trees are most susceptible can help. Infected cones and dead or dying branches should be removed and destroyed during dry weather, and pruning tools should be disinfected between cuts. Additionally, fungicides are available for treatment, with the first application recommended at budbreak.

Pine Wilt

Symptoms of pine wilt include the browning of needles, which can be limited to specific branches or occur over the entire tree. The disease spreads rapidly, and tree death can occur within three months. In most cases, trees that develop pine wilt are more than 10 years old. The disease is most common in Scotch and Austrian pines, which are highly susceptible. However, it can also affect other pine species such as Jack and mugo pines. Native pines, including white pines, are seldom affected but may be impacted if they are already suffering from other pest or disease problems or environmental stress.

There is currently no cure for pine wilt. Control measures include removing infected trees, trimming infected branches, and maintaining good cultural practices such as watering and mulching to prevent stress. In some cases, preventative injections of insecticides can be made by a tree care specialist to kill beetles and prevent infection. However, once a tree is infected, pesticides are no longer effective. Diseased trees should be destroyed by burning, chipping, or burying, and the stump should be removed or ground down to prevent the spread of the disease.

Dothistroma Needle Blight

The disease is spread by fungal spores, which are produced in the tiny, black reproductive structures of the fungus (called pycnidia). These structures erupt from the surface of infected needles. Spores are produced throughout the growing season, and infection by spores can occur at any time, but particularly during periods of cool, wet weather. Symptoms appear from five weeks to six months after infection.

To save a tree with Dothistroma Needle Blight, copper-containing fungicides can help prevent new infections, but will not cure diseased needles. Typically, a single fungicide application in early June is sufficient to protect new foliage. However, a second application three to four weeks later will provide more complete control. Several years of treatments may be needed to completely rid a tree of all infected needles.

To avoid Dothistroma Needle Blight in the future, it is recommended to avoid planting Austrian pines as they are extremely susceptible to the disease. If you already have Austrian pines, providing good air circulation, maintaining good cultural practices, not pruning after wet conditions, and applying fungicides may help control the disease.

Lophodermium Needlecast

Young trees with dense canopies are especially susceptible to infection and injury, as humidity and free moisture are more abundant. To manage Lophodermium needlecast, apply a preventative fungicide in late summer through fall. Reapply if wet weather persists.

Annosus Root Rot

Trees infected with annosus root rot begin to show symptoms 1-3 years following inoculation. Crowns will thin, turn light green to yellow, and have shortened needles that may be tufted at the branch ends. The fungus can rot the roots so badly that some trees may fall over on their own or during moderate to heavy winds. Wind-thrown trees in a pine plantation may indicate root rot. The roots of these trees can be examined for resin soaking (an early infection symptom) or for white stringy decay (an advanced infection symptom). Occasionally, the fungus will develop fruiting bodies called conks at the base of living and dead trees or stumps. These conks are hard to see because they are formed below the litter layer and are most prevalent during cool, wet winter months.

The fungus spreads most when stumps are freshly cut. Wind or splashing rain can carry the fungus from infected stumps to healthy trees with cut surfaces. After landing, the spores penetrate the wood to establish an infection. Infections can remain latent for decades before resuming growth in the pine tree. Stumps and trees with annosus root rot can also infect healthy trees through their roots.

There is a solution to prevent annosus root rot from spreading to healthy pines. Common borax powder applied to the surfaces of freshly cut stumps will help. Harvesting pines during the dry summer and fall months lowers the possibility of spread.

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