Conifer Diseases

5. Eastern and Western Gall Rusts Michael E. Ostry and Jennifer Juzwik

Revised from chapter by Glenn W. Peterson, William Merrill, and Darroll D. Skilling, 1989.

Hosts wind breakage of weakened stems at galls. the vicinity, however, suggests that the Reduced wood quality is associated with affected pine seedlings may be infected Eastern gall rust (or pine-oak gall main stem galls on older trees. Once out­- by the eastern (pine-oak) rust fungus. rust), caused by one of several formae planted, infected seedlings and young trees Conversely, the absence of oak hosts, speciales of the fungus Cronartium serve as foci for new infections, especially or the absence of infected leaves on quercuum, affects jack, Scots, shortleaf, seedlings infected with P. harknessii, Virginia, and other hard pines. Alternate because the fungus can spread directly hosts needed to complete its life cycle from pine to pine. Infection of oak seedling include a number of red oak species (sec­ leaves and older trees by C. quercuum tion Lobatae) and bur oak. The disease results in small necrotic or chlorotic areas, may be misidentified as fusiform rust that but harm to the tree is minimal. Infected is common on southern pines. In contrast, oak, in and around nurseries, serve as foci western gall rust (or pine-pine gall rust), for new infections of susceptible pine. caused by the fungus Peridermium hark­ nessii (syn. Endocronartium harknessii), Diagnosis is an autoecious fungus and needs no alternate host. Western gall rust affects Look for swellings or globose to many native hard pines of Canada and irregularly shaped galls on the stem the United States, including ponderosa, (figs. 5.1 and 5.2). Galls are rarely lodgepole, jack, Monterey, Jeffrey, Coulter, evident until the summer after the year knobcone, bishop, and gray pines. Non­ of infection. Galls formed by either native hosts that are naturally infected western or eastern gall rust fungi are by the pathogen include Scots, Aleppo, similar in size and shape and the species mugo, and Canary Island pines. cannot be distinguished based on gall shape. The presence of the characteristic Distribution brown, hair-like spore-bearing structures Figure 5.2—Aeciospores of Cronartium quercuum (telial stage of fungus) on oak leaves in on gall. Photo by Michael E. Ostry, USDA Forest Service. Eastern gall rust occurs east of the Great Plains from Canada to the Gulf of Mexico where the oak alternate hosts are present. Western gall rust is generally found throughout the pine forests of Western Canada and the United States. In the Eastern United States, it is found as far south as Virginia.

Damage Seedlings affected by eastern or western gall rust in a nursery usually do not die in the nursery. Losses in the nursery are incurred, however, when diseased seedlings are culled before shipping. Seedling death often occurs after outplanting or in older trees from Figure 5.1—Gall caused by Cronartium quercuum on pine seedling. Photo from USDA Forest Service Archive.

Forest Nursery Pests 39 Conifer Diseases

5. Eastern and Western Gall Rusts

nearby oaks suggests that observed galls Biology Chemical are caused by the western (pine-pine) rust fungus. The presence of numerous Aeciospores of C. quercuum form on Routine fungicide sprays with select­ globose to elongate galls on established galls of saplings and trees. These spores ed chemicals are effective in preventing pine stems and branches in the vicinity of are wind-disseminated to oak leaves less infection by gall rust fungi. Fungicide use the pine fields or nursery are indicative than 3 weeks old, where they infect and by nurseries varies by geographic region, of the presence of gall rust fungi. These produce repeating spores (urediniospores) however. In the Southeastern United galls are particularly conspicuous in the and teliospores. Basidiospores produced by States, fungicide sprays for fusiform rust spring when they are covered by bright the teliospores are then wind-disseminated will be effective against eastern gall rust orange masses of powdery spores called to pine in late summer-early fall where as well. aeciospores (fig. 5.3). Aeciospores of they infect needles. The fungus grows these rust fungi rarely develop on galls within needles and into the stem where Selected References found on nursery seedlings. Although galls form about 1 year after infection. Timing of the different types of spore Anderson, G.W.; French, D.W. 1965. Dif­ the aeciospores of the two fungi are ferentiation of Cronartium quercuum and production differs by region. P. harknessii morphologically identical, they can be Cronartium coleosporiodes on the basis of distinguished in the laboratory based on form orange spores on galls that morpho­ aeciospore germ tubes. Phytopathology. 55: characteristics of the germ tube length on logically resemble aeciospores but 171–173. culture plates; extended in pine-oak rust function like teliospores. On the galls, P. harknessii forms orange spores that Burnes, T.A.; Blanchette, R.A.; Stewart, and limited in pine-pine gall rust. W.K.; Mohn, C.A. 1989. Screening jack morphologically resemble aeciospores pine seedlings for resistance to Cronartium but function like teliospores. Following quercuum f. sp. banksianae and Endocronar­ dispersal, these spores germinate and tium harknessii. Canadian Journal of Forest infect needles on current year pine shoots Research. 19: 1642–1644. early in the growing season. Cummins, G.B.; Hiratsuka, Y. 2003. Illustrated genera of rust fungi, 3rd ed. St. Paul, MN: Control American Phytopathological Society Press. 225 p.

Prevention Peterson, G.W.; Merrill, W.; Skilling, D.D. 1989. Eastern and western gall rust. In: If practical, remove both oak and Cordell, C.E.; Anderson, R.L.; Hoffard, W.H.; infected pines within and around nursery Landis, T.D.; Smith, Jr., R.S.; Toko, H.V., fields. Pines resistant to both gall rusts tech. coords. Forest nursery pests. Agriculture exist and additional resistant selections Handbook 680. Washington, DC: USDA may be available in the future. Jack pine Forest Service: 36–37. seedlings from various sources have been Sinclair, W.A.; Lyon, H.H. 2005. Diseases of found to be resistant to both gall rusts, but trees and shrubs, 2nd ed. Ithaca, NY: Cornell the resistance to both is not correlated. University Press. 660 p. Thus, separate screenings are required for White, E.E.; Allen, E.A.; Ying, C.C.; Foord, the diseases on this host for areas where B.M. 2000. Seedling inoculation distinguishes both occur. Figure 5.3—Aeciospores of Cronartium quercuum lodgepole pine families most and least suscep­ being dispersed from galls. Photo by Michael E. Ostry, tible to gall rust. Canadian Journal of Forest USDA Forest Service. Cultural Research. 30: 841–843.

Culling seedlings with galls, either within beds or after lifting, minimizes shipping of gall rust infected stock.

40 Forest Nursery Pests