Atropellis Canker

About a year after infection, the fungus develops barely visible, round, black structures on the surface of the bark above the cankers. Damage includes shoot and branch injury.
Atropellis Canker - Articles

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Flagging and girdled branches symptomatic of Atropellis canker. Courtesy of Tracey Olson, PDA

Atropellis tingens Lohman and Cash (also A. apiculata Lohman, Cash, and R. W. Davidson, A. pinicola Zeller and Goodd, and A. piniphila [Weir] Lohman and Cash)

Hosts

  • Pines: Austrian, Scotch, eastern white, Jack, red, lodgepole, Ponderosa, Virginia, and others

Damage Potential

  • Moderate–severe

Symptoms and Signs

  • Small, elliptical cankers at bases of needles
  • Resin droplets at canker site
  • Clusters of small, black fruiting bodies on cankered tissue
  • Flagged (dead and brown) branches throughout tree
  • Sapwood beneath canker stained gray to black

Causes of Similar Symptoms

  • Frost damage
  • Pales weevil adult feeding
  • Diplodia (Sphaeropsis) tip blight
  • White pine blister rust

Identification

Four native North America species of Atropellis cause canker on pines. Atropellis piniphila and A. pinicola occur in the western and northwestern parts of the country, respectively. Atropellis apiculata is only found in Virginia and North Carolina. The species occurring in Pennsylvania is A. tingens. This article focuses on A. tingens.

This fungal disease of pines causes small, elliptical, blue-black cankers (or areas of dead tissue) about 0.79 inch (2 cm) long underneath the bark of twigs and branches, originating at needle bases. Small resin droplets form on the bark surface around the margins of cankers. Multiple cankers may join to girdle a twig or branch. Needles on these girdled twigs/branches begin to discolor and the twig/branch eventually dies.

These flagged branches are most noticeable in spring and early summer. In addition to patches of dead branches, this disease can also be recognized by the clusters of black, cup-shaped fruiting bodies that are 0.08–0.16 inch (2–4 mm) long and arise on the dead bark of 2- to 3-year-old cankers. Cutting into cankered areas reveals darkly stained sapwood. This distinguishes Atropellis canker from Diplodia, which discolors the wood reddish brown.

The death of branches due to A. tingens can disfigure Christmas trees, making them less economically desirable.

Biology and Life Cycle

Approximately one year after infection begins, the fungus develops barely visible, round, black structures (stromata) on the surface of the bark above the cankers. These structures produce noninfectious spores. Black, cup-shaped fruiting bodies (apothecia) form on the bark surface (Figure 1) approximately 2–3 years after infection. Apothecia are 0.08–0.16 inch (2–4 mm) in diameter and can be seen easily without magnification. Beginning in summer, these fruiting bodies swell in moist weather conditions and forcefully release infectious spores. Spore release continues through the early fall.

Figure 1. Fruiting structures of Atropellis canker on an infected Scotch pine branch. Courtesy of Tracey Olson, PDA

The fruiting bodies continue to sporulate annually, and will even do so for a short time on a standing dead or fallen tree if it remains wet. The spores are dispersed by wind and may be carried up to 328 feet (100 m) from the host plant. Spores that come in contact with healthy bark or needle scars germinate under moist conditions. The fungus enters the tree through the base of the needle. Infection occurs in living tissue and grows rapidly within the first year or two, staining the wood tissue blue black as it grows (Figure 2). Fungus growth slows after the first couple of years; after 10 years, it becomes inactive.

Figure 2. Distinctive blue-black stain is characteristic of Atropellis infection. Courtesy of Tracey Olson, PDA

Disease Cycle Calendar (Single Year’s Growth of Needles)

Monitoring and Management Strategies

Plantation Establishment

  • Plant trees with enough space between them to encourage airflow.
  • Remove and destroy any overgrown pines surrounding the proposed block to decrease chance of infection.

Preseason

  • Maintain plant vigor and health with proper fertilization.
  • Control weeds under and around trees throughout the year.
  • Scout trees for flagged branches and apothecia on the bark of infected branches.
  • Immediately prune and destroy any infected material found. Remove and destroy any tree with multiple cankers.

Growing Season

  • Continue to scout throughout the year and prune out and burn infected material.
  • At the end of the season, evaluate results and update records.

Control Options

Biological

  • No recommendations are available at this time.

Mechanical

  • Prune cankered branches 6–12 inches (15.2–30.5 cm) below the canker or where the branch attaches to the main stem. Remove and burn infected material. Disinfect shears with 70 percent alcohol or a bleach solution between cuts, as spores can be spread on tools.
  • Remove and burn trees with cankers on the main stem or trees with a heavy infection.

Biorational

  • No recommendations are available at this time.

Chemical

  • No recommendations are available at this time.

Next Crop/Prevention

  • Buy and plant disease-free stock only.