ISBN 0-662-20242-2 Cat. No. Fo 29-6/37-1992E 37 FOREST Stem rusts of pine Pest R.S. Hunt LEAFLET Pacific Forestry Centre

Introduction Hosts luteus), yellow-rattle (Rhinanthus crista-galli). Stem rusts cause more damage to Native (primary) tree hosts for these pine throughout the world than any four rusts in western Canada are jack other rust diseases of trees. They are pine (Pinus banksiana) and lodgepole Distribution caused by a well delimited group of pine (P. contorta). Western gall rust, Basically, each of these four hard-pine rust fungi which cause similar and comandra blister rust and sweet-fern stem rusts extend across North conspicuous symptoms. Damage by blister rust also occur on ponderosa America where the primary and stem rusts may cause significant pine (P. ponderosa). Other pines, alternate hosts both occur. economic impacts in commercial including several exotic species, may Interestingly, their occurrence is forests by killing trees, causing stem be infected. limited to North America; thus, distortions, or by reducing growth. In - Western gall rust may infect accidental introductions of these rusts locations where infection levels can be mugo pine (P. mugo), bishop pine (P. to other continents could seriously high, susceptible species are avoided muricata), Corsican pine (P. nigra), threaten survival and quality of pine by reforestation specialists, arborists cluster pine (P. pinaster), Monterey forests there. and horticulturists. pine (P. radiata), and Scots pine (P. Similarly, in British Columbia, In British Columbia and at other sylvestris). stem rusts occur throughout the - Comandra blister rust may infect locations in western Canada, stem contiguous ranges of their primary and Scots pine and mugo pine. rusts are represented by five species secondary host plants, although - Sweet-fern blister rust may of the fungal family Melampsoraceae: stalactiform rust is not found along the infect Bishop pine, Monterey pine, and - White pine blister rust - coast. Several areas of the province perhaps other exotic pines. Cronartium ribicola have experienced severe infection Pathologists consider all pines as and damage levels. In some - Western gall rust - primary hosts. The essential Endocronartium harknessii situations, infection levels of pine secondary hosts for these rusts are: hosts are extreme, and in such cases - Comandra blister rust - - Western gall rust - none. decisions concerning reforestation Cronartium comandrae - Comandra blister rust - and stand tending may be very difficult - Sweet-fern blister rust - Comandra (Comandra umbellata var. indeed. Cronartium comptoniae pallida and Geocaulon lividum). - Stalactiform blister rust - - Sweet fern blister rust - Sweet Cronartium coleosporoides gale (Myrica gale). Life cycles As the notorious white pine blister - Stalactiform blister rust - Indian A life cycle is the sequence of events rust is dealt with separately in this paintbrush (Castilleja species), cow in the life of an organism. Rust fungi, series of Forest Pest Leaflets (No. wheat (Melampyrum lineare), including the notorious wheat rusts 26), the remaining four are the subject lousewort (Pedicularis bracteosa), and nearly all conifer rusts, have of this leaflet. yellow owl's clover (Orthocarpus relatively complicated life cycles.

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2 Knowledge of the life history and complete host range of a tree rust is most essential, especially for development of practical silvicultural or biological control methods. Rusts are parasites typically requiring two botanically unrelated host plants in their life cycles. There are many types of life cycles in the tree rusts, but they may all be considered as variations of one basic cycle from which the others have evolved. Briefly, this basic cycle includes: the development of pycnial and aecial states on primary hosts, and the development of uredinial, telial and basidial states on secondary hosts; host-alternation from primary to secondary hosts by infection with aeciospores, and back from secondary to primary hosts by infection with basidiospores; and spread and intensification of the rust on secondary hosts by urediniospores. Following are descriptions and diagrams of the two types of the life Fig. 3. Hundreds of rust galls caused by western gall rust have girdled and killed most cycles occurring in Canadian stem branches of a mature lodgepole pine. rusts of pine: one of western gall rust (Endocronartium) which requires no secondary hosts, and the other of the blister rusts (Cronartium spp.) which require secondary hosts. The diagrams (Figs. 1 and 2) show the kind of host infected (primary or secondary host), type of spores causing the infection (aeciospores, urediniospores, or basidiospores), and time of initiation and duration of parasitism. Perennial parasitism is shown by an open spiral to indicate the indefinite duration of the disease in pine.

Western gall rust (Figs. 1, 3 and 4) Western gall rust is the most common, most conspicuous and most destructive stem rust of hard pines in western Canada. Its life cycle is also the simplest known in western Canadian tree rusts: it is completed on pine alone, without any secondary hosts. In spring and early summer, an orange powder consisting of millions of spores is released from galls of the diseased pines. These spore masses, Fig. 4. Multiple infection of lodgepole pine by western gall rust; note the oblong or pear- shaped form of the galls.

3 attacked and killed by secondary insects and fungi. At that time the fungus dies and spore production ceases.

Comandra, sweet-fern and stalactiform blister rusts (Figs. 2 and 5-10) These stem rusts differ distinctly from each other in their requirements for specific secondary hosts, but only slightly in microscopic characteristics and symptoms. Their life cycles are essentially alike and will therefore be outlined together. In spring and early summer, white blisters break through the bark of stem cankers or swollen branches of pine and release orange aeciospores. Often, wind disperses them, frequently over large areas. The aeciospores cannot infect other primary hosts (pines), but only secondary hosts. Specifically, aeciospores of comandra blister rust can infect only comandra, Fig. 5. Stem of six-year-old Monterey pine almost girdled by sweet-fern blister rust. aeciospores of sweet-fern blister rust The spore blisters have ruptured and most only sweet gale, and aeciospores of of the aeciospores are shed. stalactiform blister rust only Indian paintbrush and a few other herbs of the figwort family (see “Hosts”). On Fig. 6. Typical elongate canker of the leaves of its secondary hosts, stalactiform blister rust with white spore resembling little clouds of dust, are blisters containing the orange spore dispersed by wind currents. After each rust causes irregular orange to masses. landing on other susceptible (hard) brownish yellow spots. The pines, especially after periods of rain, urediniospores, teliospores, and some of the spores will germinate and basidiospores develop on the temperature. Unless they land on cause new infections. Depending underside of the leaves within these susceptible pine shortly after they are partly on wind velocity and direction spots. The urediniospores are disseminated and climatic conditions during spore dissemination, the formed during the summer are suitable, they perish. disease may spread over long approximately 2 weeks after Only basidiospores can initiate distances, sometimes hundreds of infection. They serve to intensify the the disease in pine. The point of initial kilometres. The succulent elongating rust on its secondary hosts; they infection on pines may vary with the branch or cone tissue is the entry cannot infect primary hosts (pines). rust species. The first disease point for the fungus. Approximately 2 “Telial horns” (Fig. 10), consisting of symptoms (discoloration of the foliage years after infection, the first columns of teliospores, develop on followed by progressive swelling of the symptoms begin to appear: irregularly the leaves during mid-summer and bark) appear approximately 3 years round to pear-shaped galls. On these fall. The teliospores germinate and after infection. The pycnial stage galls white blisters break through the produce basidiospores which may probably forms during this time. It is a bark each spring, releasing their infect pines after being disseminated. spermatial stage responsible for orange spores after they burst. The The basidiospores cannot infect other fertilization of cankers via insects, in life cycle of western gall rust is thus secondary hosts, but only primary order that aecial spores can be completed. hosts (pines). produced. It is rarely seen. In spring The galls of western gall rust are Basidiospores represent the of the following year, white blisters woody and perennial, growing larger weakest link in the life cycle. They are appear and aeciospores are again each year and producing new crops of small, delicate, and unable to survive liberated, marking the beginning of a spore blisters until they have been even a few hours of drought or high new life cycle.

4 Fig. 7. Ellipsoid or egg-shaped aeciospores (right) and fusiform Fig. 8. Pear-shaped aeciospores of Cronartium comandrae. The filament cells (left) of Cronartium coleosporioides (x 520). aeciospores of other pine stem rusts (Fig. 7) are ellipsoid or egg- shaped (x 520).

As in western gall rust, the cankers with copious resin flow summer, surveys of pine for the disease is perennial in pine. Annually, reaching lengths of 6 metres or more, presence of stem rust should be aeciospores are produced on pine or woody branch galls (Figs. 3 and 4) carried out in late spring and early until the affected stems or branches or gall-like excrescences (hip cankers) summer. are dead from attack by secondary on stems. Rodents, attracted by the Rusted secondary hosts also are organisms. At that stage the fungus sugars in the thickened succulent bark indicative of the presence of pine stem dies out, too, and no further crops of of infected areas, feed on the rust in an area. For instance, if Indian paintbrush (Castilleja spp.) were found aeciospores are produced. Unlike diseased bark at the margins of rust rusted with Cronartium, one would western gall rust, the three blister cankers, generally causing severe expect at least some of the pines in rusts are entirely dependent on their resin flow. Frequently, such damage the vicinity to be diseased with secondary hosts for survival: pine to pine has been ascribed to rodents stalactiform blister rust. Pine stem infection can result only from alone, and rust has not been rust (Cronartium spp.) on secondary basidiospores produced on nearby recognized as the primary cause. secondary hosts. hosts can be easily identified in the Except for western gall rust, late summer or fall by the crowded symptoms alone are insufficient for Recognition groups of minute, yellow-brown hairs identification of pine stem rusts. (telial horns) on the underside of Flagging - the reddening of all needles The only reliable characteristic for diseased foliage (Fig. 10). Secondary of recently killed branches - is the identification of stem rust is spore hosts can thus be very useful for most conspicuous indication of stem blisters on the diseased stems and detection and identification of stem rust in a pine stand. But flagging may branches (Figs. 4, 5 and 6). These rusts in the field. also be caused by other branch blisters contain the aeciospores, A key for preliminary identification diseases. Other symptoms indicating intergrown with threads (filaments) of western Canadian stem rusts of stem rust are cankers (Figs. 5, 6 and projecting from the inner walls of the pine is shown on the following page. 9) or roughened bark at the swollen blisters (Fig. 7). Since the blisters Stalactiform and sweet-fern rusts base of dead or dying branches, trunk disintegrate and disappear by late are very much alike, but they can be

5 Features for identification of stem rusts of pine in western Canada.

Spore blisters on stems or branches of soft (five-needle) pines; Spore blisters on stems or branches of hard (two- particularly found in vicinity of currants and gooseberries and three-needle) pines

White-pine blister rust (see Forest Pest Leaflet No. 26) Spore blisters on slight to Spore blisters on woody distinct spindle-shaped globose or pear-shaped galls of swellings of branches or stem branches or stems

(Figs. 3 and 4) Western gall rust Spores pear-shaped, often Spores oblong or ellipsoid (as seen pointed on one or both ends (as under a microscope, Fig. 7) seen under a microscope, Fig. 8); canker length to width ratio less than 10:1

spore warts of equal length; found in vicinity spore warts tallest opposite of Indian paintbrush and other susceptible smooth spots; found in vicinity (Figs. 8-10) plants of the figwort family; canker length to of sweet gale Commandra blister rust width ratio, greater than 10:1

(Fig. 5) Sweet-fern blister rust (Figs. 6 and 7) Stalactiform blister rust

identified reliably by determining their quickly (Figs. 5, 6 and 9), but in larger (Figs. 3 and 4). The rust also affects secondary hosts with inoculation trees progress of the disease and the growth rates of pines, as well as experiments, or by careful observation subsequent death of the tree is lumber quality and quantity. of the warts on the aeciospores. slower. Branch infections near the Pines are valuable timber trees stem must grow into the stem before in British Columbia. For instance, DAMAGE girdling the tree and therefore lodgepole pine, occurring from sea Mortality and growth losses are the damage is slower than direct stem level to subalpine elevations and principal forms of damage resulting infections. Damage by sweet-fern likely to be found on almost any from pine stem rust infections, blister rust is more or less restricted forest site in western Canada, is used although none of the native blister to young trees; it is seldom serious in for railroad ties, mine timbers, poles, rusts will completely prevent natural stands but has been very posts, fuel wood, rough construction, development of a merchantable damaging to Monterey (Fig. 5) and and planing-mill products such as stand. Intensity of damage in pine bishop pine plantations in British siding, finish and flooring. It is also a stands varies greatly, depending on Columbia. With the other stem rusts, valuable species in the manufacture susceptibility of the pine species and trees of all sizes and ages are of pulp. even of individual trees within a attacked but seedlings and saplings species, climate and (except in are especially susceptible. Trees that CONTROL western gall rust) the proximity and survive western gall rust in the abundance of secondary hosts. In seedling stage may continue to Treatment of infected pines with seedlings and saplings, stem develop branch galls until a large systemic fungicides has been infections will girdle the tree relatively proportion of the branches are killed attempted, but without success.

6 Fig. 9. Typical spindle-shaped comandra rust canker on the main stem Fig. 10. Comandra shoot covered with abundant telial horns of of a ponderosa pine seedling. The crackling and pitting of the bark on Cronartium comandrae. (U.S. Forest Service photo.) swollen areas is caused by aecia rupturing the bark. Seedlings with infections on main stems survive only a few years. (U.S. Forest Service photo by R.G. Krebill.)

Protective fungicides can work in especially important where infection Selected References nurseries, but these are unnecessary is caused by western gall rust, which Boyce, J.S. 1961. Forest pathology, if alternate hosts or nearby gall rust lacks a secondary host. Nurseries of 3rd ed., McGraw-Hill Book infected pines are removed. pine should not be established in Company, Inc., New York, Eradication of the secondary hosts is areas where stem rusts or their Toronto, London. usually only economically feasible for secondary hosts are abundant. Pine British Columbia Ministry of Forests. nursery situations. plantations which have failed due to 1988. Protection Manual. Vol. II. In young growth stands removal stem rust attack should be replanted Pest Management. Chap. 7, of infected trees and pruning of with tree species other than pine. Stem, Canker and Foliage branches during spacing are the only There is variation in susceptibility Diseases, 41 p. practical means of control at present. to stem rusts among provenances and Byer, J.W.; Cobb, F.W.; Parmeter, J.R. In mature forests damage can be within families; therefore, a resistance 1972. Occurrence and minimized by cutting in heavily rusted selection or breeding program for significance of fungi inhabitory galls stands first, thus preventing some of disease resistance is feasible. caused by Peridermium harknessii. the continuing spread and mortality Can. J. Bot. 50:1275-1282. from old cankers. Finck, K.E.; Humphrey, P.; Hawkins, In nurseries, it is important that G.V. 1989. Field guide to pests infected stock be destroyed and not of managed forests. For. shipped to prevent establishment of Can./B.C. Min. For. Joint Publ. new infection centers. This is No. 16, pp. 67-76.

7 Hiratsuka, Y. 1969. Endocronartium, Peterson, R.S.; Jewell, F.F. 1968. Additional Information a new genus for autoecious pine Status of American stem rusts of stem rusts. Can. J. Bot. pine. Ann. Rev. Phytopathol. Additional copies of this and other 47(9):1493-1495. 6:23-40. leaflets in this Forest Pest Leaflets Hunt, R.S. 1983. White pine blister Sinclair, W.A.; Lyon, H.H.; Johnson, series, as well as additional scientific rust in British Columbia. Can. For. W.T. 1987. Diseases of trees details and information about Serv. For. Pest Leafl. No. 26, 4 p. and shrubs. Cornell Univ. Press, identification services, are available Martinsson, O. 1980. Stem rusts in Ithaca, N.Y., pp. 270-283. by writing to: lodgepole pine provenance trials. van der Kamp, B.J.; Spence, M. Silvae Genetica 29:23-26. 1987. Stem diseases of lodgepole Natural Resources Canada Mielke, J.L. 1956. The rust fungus pine in the British Columbia Canadian Forest Service (Cronartium stalactiforme) in interior following juvenile spacing. Pacific Forestry Centre lodgepole pine. J. For. 54:518-521. For. Chron. 64:334-339. 506 West Burnside Road Mielke, J.L.; Krebill, R.G.; Powers, Wood, C. 1986. Distribution maps Victoria, B.C. V8Z 1M5 H.R., Jr. 1968. Comandra blister of common tree diseases in www.pfc.forestry.ca rust of hard pines. USDA For. British Columbia. Can. For. Serv., For. Pest Leafl. 62. Serv. Pac. For. Cent. Inf. Rep. Phone (250) 363-0600 Molnar, A.C. 1961. An outbreak of BC-X-281, 68 p. Cronartium comptoniae on Ziller, W.G. 1967. Sweetfern blister © Her Majesty the Queen in Right of Monterey and bishop pines on rust. Cronartium comptoniae Canada, Revised October 1992 Vancouver Island, British Arth. Pages 181-183 in Important Columbia. Plant Dis. Rep. forest insects and diseases of PDF Version January 2001 45:854-855. mutual concern to Canada, the Peterson, R.S. 1960. Western gall United States and Mexico. Can. rust on hard pines. USDA For. Dep. Forest. & Rural Serv. For. Pest Leafl. 50. Development, Pub. No. 1180. Peterson, R.S. 1967. The Ziller, W.G. 1974. The tree rusts of Peridermium species on pine western Canada. Env. Can., stems. Bull. Torrey Bot. Club Can. For. Serv. Publ. No. 1329, 94(6):511-542. 272 p.

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