Symptom Identification and Control Methods of Red Pine Bark Rot

Red pine bark rot, also known as weeping branch disease, soft branch disease, dead branch disease, and shoot blight, is a type of branch and trunk canker disease that mainly affects pine species.

Symptoms: The disease affects the bark of branches and trunks of young red pine trees, and in severe cases can also occur at the base of the trunk, causing cankers. Pine needles above the infected area turn yellow-green to gray-green, and gradually turn brown to reddish-brown. The affected branches and trunks shrink and wrinkle due to water loss, and the needle drop scars appear slightly swollen. When the base of a lateral branch is infected, the lateral branch droops downward. When the base of a twig is infected, it shows symptoms of dead branch disease. When the main trunk is infected, the diseased area exudes resin, cankers form with a rotten bark appearance, the diseased bark gradually shrinks and sinks, and resin flow intensifies. Starting in April, cracks form in the cortex of the diseased area, from which yellow-brown disc-shaped structures emerge; these are the ascocarps of the pathogen. The ascocarps number 1 to several in clusters, gradually develop and enlarge, darken in color, and expand into disc shapes clustered together when exposed to rain. After drying, they shrink and turn black, with edges curling toward the center from two sides or three directions.

Pathogen: The pathogen is Cenangium ferruginosum Fr. ex Fr., belonging to the Ascomycota, Discomycetes, Helotiales fungi.

Disease pattern: The disease affects branches and trunks of young trees over 4 years old. The pathogen overwinters as mycelium in the diseased bark of infected plants. In the following spring, pine needle blight symptoms appear, and from March to mid-April, ascocarps emerge from the bark. The ascocarps mature from late May to late June and release spores. Ascospores can be released continuously for about 3 months. The spores spread by wind and rain, germinate under wet conditions, and invade the bark through wounds, with symptoms appearing after overwintering. The pathogen often lives on the lower lateral branches of trees, actively decomposing dead bark on dead branches and promoting natural pruning, which is why it is also called the pruning fungus. When pine trees are weakened by drought, waterlogging, frost, insects, overcrowded planting, or poor soil, it can infect the weakened bark of branches and trunks, causing bark rot symptoms. In addition, when young trees are weakened by damage from aphids and scale insects or snow pressure, the disease spreads rapidly, causing huge losses.

Control: (1) Match tree species to suitable sites, carry out timely tending, prune reasonably, and remove dead standing trees and diseased trees. (2) Control pests such as aphids and pine bast scales. (3) Spray trunks with 1:1:100 Bordeaux mixture or 2 degrees Baume lime sulfur mixture, or apply pine tar or 0.2% mercuric chloride diesel oil solution to branches and trunks for treatment.