White Pine Blister Rust Forest Health Protection USDA Forest Service

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White Pine Blister Rust Forest Health Protection USDA Forest Service 2013 Forest Health Protection and State Forestry Organizations Management Guide for John Schwandt and Holly Kearns White Pine Blister Rust Forest Health Protection USDA Forest Service Cronartium ribicola Fisch. This fungus disease was Conifer hosts: accidentally introduced from needled pines Topics All native five- Europe in 1910. Since then, it has devastated western white pine and Introduction 1 Alternate hosts: whitebark pine forests in the Life History 2 Ribes spp. (currants and northern and central Rocky gooseberries) are the main Mountains. Recognition 3 alternate hosts. Management 4 Resistance 4 Introduction Cultural practices 4 Management of western white pine This fungus has two host types that Pruning 5 has been confounded by the are both required to complete its life Exising 7 introduction of white pine blister cycle. One host is a five-needled pine Thinning 7 rust, caused by the fungus Cronartium and the other is a shrub or Ribes management 8 ribicola Fisch. This disease was herbaceous host, referred to as the introduced into western North alternative host. Prioritizing stands 9 America from Europe in 1910 on Monitoring 9 On pines, the fungus causes branch infected eastern white pine seedlings flagging and stem cankers that Leave tree selection 10 grown in France and planted near eventually cause top kill or death. All Other Reading 10 Vancouver, BC. Western white pine sizes of trees are attacked and small proved to be highly susceptible to Field data sheet 12 seedlings can be killed rapidly. blister rust with mortality rates of 90 Generally, the larger the tree is at the percent or more in what were once time it becomes infected, the longer vigorous, well-stocked stands. The Key Points it survives after infection. On the disease is now distributed throughout The cause of this alternate hosts, damage is usually the range of the pine hosts in the confined to small leaf spots but disease is an northern and central Rocky invasive species. minor defoliation ay occur if severely Mountain region. infected. Forests have been dramatically altered by this WHITE PINE BLISTER RUST MANAGEMENT SUMMARY disease. Four major goals for integrated management of western white pines: Pruning can save stands. 1. Breed for resistance. Use breeding programs that will incorporate desirable silvical characteristics as well as rust resistance while Monitor to schedule minimizing selection pressure on the rust. treatment and assess resistance. 2. Prune and thin. Prune and thin to remove and minimize infections. Hazard rate sites to 3. Hazard rate sites. Rate sites for potential blister rust damage. select the best 4. Maintain genetic diversity. Maintain genetic diversity by management. encouraging white pine leave trees. Page 2 White Pine Blister Rust Life History White pine blister The white pine blister rust fungus is nearby. In late summer the fungus rust requires two host types to an obligate parasite which means it produces teliospores on small hair- complete its life can only survive on living host like projections on the underside of cycle. tissue. It has a complex life cycle leaves of the alternate hosts. These that includes five spore stages on soon produce very fragile spores Conifer hosts— two different hosts. Cankers on (basidiospores) which usually travel All native five-needled white pine produce characteristic very short distances to infect pines including western white pine (Figure 1), yellow-orange blister-like aecia that current- and one year-old needles of limber pine, whitebark erupt through the bark in spring. pine, sugar pine, and bristlecone pine. Figure 5. Telia on underside of ribes leaf in the fall. [Photo by J. Schwandt] Figure 3. Aecia on a whitebark pine branch. [Photo by J. Schwandt] white pines. During spring, the fungus kills leaf Aeciospores from these blisters can tissue resulting in small leaf spots, travel long distances to infect leaves then grows into adjacent twigs and of the alternate hosts. Figure 1. Rust stem canker. branches. The fungus grows along During summer, pycniospores are branches about 2-4 inches per year Alternate hosts— produced near canker margins in toward the main stem, killing tissue Mostly Ribes spp.(currants watery droplets which insects carry as it advances. Cankers within six and gooseberries). from canker to canker resulting in Research has recently fertilization of the rust fungus. shown some species of Pedicularis (lousewort) and Castilleja (Indian paint brush) can also be infected, but their role has yet to be determined. Figure 6. New canker (orange discoloration) in a twig. [Photo by J. Schwandt] Figure 4. Pycniospores exuding from an inches of the bole may continue to infected pine twig. [Photo by J. Schwandt] grow several years, even in branches that have no live foliage remaining. Cankers on branches and young The fungus builds up on the stems generally produce aecia 3-5 alternate hosts through the summer years after needle infection, but by producing spores (urediospores) Figure 2. Spots on a Ribes leaf. sporulation can be very sporadic. which reinfect alternate hosts White Pine Blister Rust Page 3 Recognizing rust infections New infections fungus only has minimal effects on Figure 9. the rust, but may help to identify Wetting makes cankers Although the fungus causes small easier to see. needle spots the spring after rust cankers. infection, the earliest obvious Rodent chewing on western white symptom is usually discoloration, pine (figure 9) has almost always swelling, or pitch flow on an been an indicator of rust infection infected twig or branch. As the since rodents are attracted to high fungus girdles the branch, the sugar concentrations in cankers. needles beyond the canker die creating distinctive “flags” (figure 7). The bark at the canker center becomes sunken or cracked while the leading margin of a canker is A branch canker showing more distinct discoloration after wetting with water. Figure 8. Rodent chewing on white pine bark is almost always an indication of a blister rust canker. [Photo by J. Schwandt] Figure 10. Abnormal Figure 7. Branch flag caused by a canker Stem cankers girdling the branch. [Photo by J. Schwandt] stem cankers. Infected trees may appear vigorous yellow to brown. (The canker until shortly before death (> 90% margin can usually be made more girdle), although stem cankers visible by washing and lightly usually have abundant resin flow on scrubbing with water). the outer bark. Sporulation Abnormal cankers may also be Characteristic sporulating yellow found, especially on trees with blisters near the canker margins are some level of natural resistance. produced in the spring, but may These can appear as slow growing not occur until many years after cankers with swollen callus ridges infection, and may not occur every and sunken centers or year. During the summer, cankers misshapened areas at the base of may produce watery droplets of small trees that can easily be pycniospores that ooze out from mistaken for mechanical damage inside canker margins and leave or root disease infection (figure dark brown spots (pycnial scars) 10). Trees with basal cankers may which can aid in canker be bent by snow or chewed by identification. rodents which may make identification difficult. Trees with Other fungi and rodent chewing root disease usually have an During periods of high moisture irregular “canker” margin without cankers may be partially covered any yellow discoloration at the top with a pink-purple weakly parasitic and copious resin that increases fungus called Tuberculina. This below ground line. Page 4 White Pine Blister Rust Management Considerations There are four major goals for practices such as pruning and integrated management of western thinning to remove and minimize white pines: (1) use breeding infections (3) develop hazard rating programs that will incorporate systems that will help rate sites for desirable silvical characteristics as infection potential, and (4) maintain well as rust resistance while genetic diversity by encouraging minimizing selection pressure on leave trees. the rust, (2) use silvicultural Figure 11. White pine blister rust resistance offers the best long Breeding for resistance term solution for the restoration of white pines. [Photo by S. Hagle] A cooperative western white pine overcome host resistance. Strains tree improvement program to of C. ribicola that have overcome capture and concentrate naturally resistance in western white pine occurring resistance mechanisms have been discovered in Oregon was started in 1959. The early and California. These populations crosses proved resistance traits are being closely monitored and so could be successfully passed on far have not spread far from their White Pine Tree through breeding and nearly 15 origin. Because of the potential for Improvement years later seed was operationally the rust to change, there is an Program Goals available from this first generation ongoing program to select and test (F1) of selectively bred trees additional parent trees exhibiting (Sandpoint, Idaho seed orchard). resistance. The testing is Produce seedlings The best candidates from the first conducted at the Coeur d’Alene that have good breeding were crossed to create a nursery where seedlings from silvical second generation (F2) to further potentially resistant trees are characteristics improve resistance. F2 seed subjected to an intense spore load orchards were established at under favorable infection Resistance levels Moscow, Lone Mountain, and conditions. Trees are checked for that will provide Coeur d’Alene, Idaho. Most of the resistance and good growth good survival while white pine planted since the mid characteristics for 3 years and the minimizing 1980s have been F2 stock from best performers are being added to selection pressure these seed orchards (Moscow was a new seed orchard established in on the rust. phased out in the early 1990s). A 1986 at Grouse Creek, Idaho. The single green house test of this stock goal is to produce seedlings that reported that 66% of this stock have good silvical characteristics as would remain canker free.
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