Elliptical cankers covered with yellow blisters that release infectious spores to be carried away by the wind. Courtesy of Tracey Olson, PDA
J. C. Fisch
- Eastern white pine (Pinus strobus)
- Other five-needled pines
- Other Ribes species
Symptoms and Signs
- Chlorotic needles, stunted growth
- Chlorotic, dead, or dying tree tops or branches
- Yellow-bordered cankers on trunk or 3- to 4-year-old branches; oozing resin or rodent feeding may be apparent
- Resin flow on main trunk that hardens to white, orange, or brown
- Orange-yellow blisters breaking through cankered bark to release spores
Late spring to early summer:
- Sticky, yellow fluid produced from yellow-brown blister on canker; fluid will blacken after a short time
- Patches of yellow or brown bark on young growth; area may be swollen but progresses to spindle-shaped canker by second year of infection
On Ribes Species
- Orange spores on underside of leaf; upper surface may have yellow, diffused spots
Late summer to early fall:
- Brown, hairlike projections on underside of leaf
Causes of Similar Symptoms
- Fungal root rots
- Pales weevil
- Pine root collar weevil
White pine blister rust is the only stem rust of five-needled pines. It requires an alternate host (Ribes species) for new infections to occur on pine.
Early detection can be difficult due to very subtle symptoms during the first year of infection. First, a small, yellow or red spot appears on the needle at the site of infection and eventually the needle may die as the fungus grows into the bark tissue. The newly infected bark tissue will become brown with a yellow border surrounding a section of dead needles. The stem may be slightly swollen.
During the second year of infection and beyond, long, elliptical-shaped cankers develop on branches and the main trunk as the fungus advances. Cankers can eventually girdle the branch, which results in “flagging” (Figure 1), or they can girdle the trunk, killing all growth above the canker. Yellowish-green bark tissue may be visible around the canker. Blisters (0.25 inch, 3 mm across), spores, and resin fl ow all arise from the canker area. Rodent feeding may be evident around this area as well.
Figure 1. Flagging as a result of cankers girdling a branch. Courtesy of John W. Schwandt, USDA Forest Service, Bugwood.org (#1241718)
Biology and Life Cycle
The life cycle of white pine blister rust may take 3–6 years to complete. It begins in late summer or early autumn when basidiospores from the alternate host (Ribes species) are wind and rain dispersed, entering the pine needle through the stomata (Figure 2). Basidiospores may be carried in wind currents for up to a mile.
Figure 2. Yellow/red infection site on a needle. Courtesy of USDA Forest Service Ogden Archive, Bugwood.org (#1467424)
The fungus grows into the bark tissue at a rate of 5–6 inches (12.5–15.0 cm) per year and begins to form cankers after the first year of infection (Figure 3). In spring, 3–4 years after the initial infection, pale yellow or cream-colored blisters (aecia) rupture through the bark of active cankers (Figure 4). They release powdery, yellow spores (aeciospores) that are carried in the wind over long distances to the alternate host and cause infection. The aeciospores can only infect Ribes species. After the spores are released, the cankered area on the pine remains swollen and roughened. In summer, the sticky, yellow fluid that exudes from the site hardens and leaves small, brown-rust-colored scars (Figure 5).
Figure 3. Elliptical cankers formed after the first year of infection. Courtesy of Joseph O’Brien, USDA Forest Service, Bugwood.org (#5061066
Figure 4. Mass of powdery, yellow spores covering the surface of the canker (spring). Courtesy of Tracey Olson, PDA
Figure 5. Sticky, yellow liquid exuded by a canker just before hardening off. Courtesy of Joseph O’Brien, USDA Forest Service, Bugwood.org (#5042098)
On the alternate host, the aeciospores enter the stomata of the leaf during wet weather. Diffused, yellow spots become visible on the upper leaf surface soon after infection occurs. Within a few weeks, pustules form on the leaf underside and release spores that repeatedly infect the same plant or other Ribes in the vicinity (Figure 6). This repeating stage serves to increase the levels of inoculum. In late summer, small, brown, hairlike structures appear on the under-side of the leaf. Eventually, basidiospores are produced and wind dispersed back to susceptible pines in the vicinity.
Figure 6. Underside of Ribes leaf with fruiting bodies. Courtesy of Robert L. Anderson, USDA Forest Service, Bugwood.org (#0355052)
Monitoring and Management Strategies
- Northeastern Pennsylvania is especially prone to white pine blister rust.
- Do not plant white pine in low-lying areas where cool, moist air is likely to settle.
- Do not plant white pine species if there is an abundance of alternate hosts (Ribes spp.) in the surrounding area.
- Consider removing alternate host material from within 1,000 feet of white pine plantings.
- Tag trees suspected to have white pine blister rust to check for blisters in mid-April.
- Scout trees for blisters in mid-April.
— Randomly select at least 50 trees that are 5–10 years of age.
— Look for yellow or orange blisters on branches and trunks.
— Also scout tagged trees.
- If 10 percent or more of sampled trees are infected:
— Prune/remove cankers from trees before infection reaches trunk.
— Control alternate host before August.
- Remove and destroy trees with trunk infections.
- Inspect trees throughout the year for cankers.
- At the end of the season, evaluate results and update records.
- No recommendations are available at this time.
- Prune and destroy all branches with cankers.
- Remove and destroy all alternate host plants in and around plantation within a minimum of 1,000 feet.
- No recommendations are available at this time.
- Apply an appropriate fungicide in late summer to protect pines from infection from basidiospores released by an alternate host.
- Apply an appropriate herbicide to control the alternate host.
- Inspect plants/nursery stock; buy from a reputable company.