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WHITE PINE BLISTER RUST Cronartium Ribicola J. C. Fisch

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WHITE PINE BLISTER RUST Cronartium Ribicola J. C. Fisch Hosts Causes of Similar Symptoms WHITE PINE • Eastern white pine (Pinus strobus) • Fungal root rots • Other fi ve-needled pines • Pales weevil BLISTER RUST • Pine root collar weevil Cronartium ribicola Alternate Hosts J. C. Fisch • Currants Identifi cation • Gooseberry White pine blister rust is the only stem rust • Other Ribes species of fi ve-needled pines. It requires an alter- nate host (Ribes species) for new infections Damage Potential to occur on pine. • Moderate–high Early detection can be diffi cult due to very subtle symptoms during the fi rst year of Symptoms and Signs infection. First, a small, yellow or red spot On Pine appears on the needle at the site of infection Year-round: and eventually the needle may die as the • Chlorotic needles, stunted growth fungus grows into the bark tissue. The newly infected bark tissue will become brown with • Chlorotic, dead, or dying tree tops or a yellow border surrounding a section of dead Elliptical cankers covered branches with yellow blisters that needles. The stem may be slightly swollen. release infectious spores to • Yellow-bordered cankers on trunk or During the second year of infection 3- to 4-year-old branches; oozing resin or be carried away by the wind. and beyond, long, elliptical-shaped cankers Courtesy of Tracey Olson, rodent feeding may be apparent develop on branches and the main trunk as PDA • Resin fl ow on main trunk that hardens to the fungus advances. Cankers can eventu- white, orange, or brown ally girdle the branch, which results in Early spring: “fl agging” (Fig. 1), or they can girdle the • Orange-yellow blisters breaking through trunk, killing all growth above the canker. cankered bark to release spores Yellowish-green bark tissue may be visible Late spring to early summer: around the canker. Blisters (0.25 inch, • Sticky, yellow fl uid produced from 3 mm across), spores, and resin fl ow all arise yellow-brown blister on canker; fl uid from the canker area. Rodent feeding may will blacken after a short time be evident around this area as well. Fall: Biology and Life Cycle • Patches of yellow or brown bark on young growth; area may be swollen but The life cycle of white pine blister rust may progresses to spindle-shaped canker by take 3–6 years to complete. It begins in late second year of infection summer or early autumn when basidiospores from the alternate host (Ribes species) On Ribes Species are wind and rain dispersed, entering the Summer: pine needle through the stomata (Fig. 2). • Orange spores on underside of leaf; upper Basidiospores may be carried in wind surface may have yellow, diffused spots currents for up to a mile. Late summer to early fall: • Brown, hairlike projections on underside of leaf Figure 1. Flagging as a result of cankers girdling Figure 2. Yellow/red infection site on a needle. a branch. Courtesy of John W. Schwandt, USDA Courtesy of USDA Forest Service Ogden Forest Service, Bugwood.org (#1241718) Archive, Bugwood.org (#1467424) WHITE PINE BLISTER RUST ...................................................................................................................................................................................................................................... ................................................................................................... 71 99 The fungus grows into the bark tissue • Consider removing alternate host at a rate of 5–6 inches (12.5–15.0 cm) per material from within 1,000 feet of year and begins to form cankers after the white pine plantings. fi rst year of infection (Fig. 3). In spring, 3–4 years after the initial infection, pale yellow Preseason or cream-colored blisters (aecia) rupture • Tag trees suspected to have white pine through the bark of active cankers (Fig. blister rust to check for blisters in 4). They release powdery, yellow spores mid-April. Figure 3. Elliptical cankers (aeciospores) that are carried in the wind formed after the fi rst year of over long distances to the alternate host Growing Season infection. Courtesy of Joseph and cause infection. The aeciospores can • Scout trees for blisters in mid-April. O’Brien, USDA Forest Service, Bugwood.org (#5061066) only infect Ribes species. After the spores — Randomly select at least 50 trees that are released, the cankered area on the pine are 5–10 years of age. remains swollen and roughened. In summer, — Look for yellow or orange blisters on the sticky, yellow fl uid that exudes from the branches and trunks. site hardens and leaves small, brown-rust- — Also scout tagged trees. colored scars (Fig. 5). • If 10 percent or more of sampled trees are On the alternate host, the aeciospores infected: enter the stomata of the leaf during wet weather. Diffused, yellow spots become — Prune/remove cankers from trees before infection reaches trunk. visible on the upper leaf surface soon after — Figure 4. Mass of powdery, infection occurs. Within a few weeks, pus- Control alternate host before August. yellow spores covering the tules form on the leaf underside and release • Remove and destroy trees with trunk surface of the canker (spring). spores that repeatedly infect the same plant infections. Courtesy of Tracey Olson, PDA or other Ribes in the vicinity (Fig. 6). This • Inspect trees throughout the year for repeating stage serves to increase the levels cankers. of inoculum. In late summer, small, brown, • At the end of the season, evaluate results hairlike structures appear on the under- and update records. side of the leaf. Eventually, basidiospores are produced and wind dispersed back to Control Options susceptible pines in the vicinity. Biological • No recommendations are available at this time. Mechanical • 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. Figure 5. Sticky, yellow liquid Figure 6. Underside of Ribes leaf with exuded by a canker just before fruiting bodies. Courtesy of Robert L. Biorational hardening off. Courtesy of Anderson, USDA Forest Service, • No recommendations are available Joseph O’Brien, USDA Bugwood.org (#0355052) Forest Service, Bugwood.org at this time. (#5042098) Monitoring and Management Chemical Strategies • Apply an appropriate fungicide in late summer to protect pines from infection Plantation Establishment from basidiospores released by an alternate • Northeastern Pennsylvania is especially host. prone to white pine blister rust. • Apply an appropriate herbicide to control • Do not plant white pine in low-lying areas the alternate host. where cool, moist air is likely to settle. • Do not plant white pine species if there Next Crop/Prevention is an abundance of alternate hosts • Inspect plants/nursery stock; buy from a (Ribes spp.) in the surrounding area. reputable company. SHOOT AND BRANCH INJURY ............................................................................................................................................................................................................................................................ 100.
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