Glenn W. Peterson1 and C. S. Hidges, Jr.2
|1Plant Pathologist, U.S. Department of
Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment
Station, Lincoln, Nebr.
2 Plant Pathologist, U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station, Institute of Pacific Islands Forestry, Honolulu, Hawaii.
|Phomopsis blight has been a serious problem for more than 75 years in nurseries producing juniper seedlings and grafts. Phomopsis juniperovora Hahn, the fungus causing this disease, is widespread in the United States (fig. 1).||
Figure 1. States in which Phomopsis juniperovora is present.
Losses have been most severe in seedling and transplant beds of eastern redcedar and Rocky Mountain juniper. (See cover photo.) Other junipers are susceptible, as are some species in the genera Chamaecyparis, Cupressus, and Thuja. Arizona cypress seedlings have been seriously damaged in some Southern States.
Phomopsis juniperovora initially infects foliage, then spreads to and sometimes kills stem tissues. Newly developing needles are especially susceptible while they are still in the yellowish-green stage; after needles become a normal deep green, they are no longer susceptible. Small yellow spots appear on young needles of eastern redcedar and Rocky Mountain juniper within 3 to 5 days after infection.
Figure 2.Top of seedling killed after spread of the fungus from branch to stem.
|The fungus ramifies within infected needles and rapidly invades and girdles young stems. When a side shoot is infected, the fungus progresses to the main stem, which it may girdle if the stem is less than I centimeter (0.39 in) in diameter. The portion of the seedling above the girdled area then dies (fig. 2). At first, infected tissues turn light green; but they rapidly change to the characteristic red-brown color of dead shoots, which finally turn ashen gray. Lesions on larger stems frequently develop into cankers, but the stems are not girdled. The fungus does not spread far below cankers. Survival of even lightly blighted nursery stock in outplanting sites is very poor because new shoots continue to be infected by spores produced on old, infected tissues.|
|When junipers in landscape plantings become infected, they may become unsightly because of numerous dead branch tips (fig. 3). Older trees are seldom killed because only small-diameter stems are girdled. For this reason, Phomopsis blight does not cause significant damage in natural stands of junipers.|
|Total loss of first-year seedlings is common in epidemic years if control
measures are not used. Losses are particularly high in areas w ere water tends
to stand and in new seedlings adjacent to beds of infected stock. Some of the
worst epidemics occur late in the growing season, when there is a late flush o
growth on juniper seedlings.
Damage from drought may be confused with Phomopsis blight. In both cases, tips of branches may be killed. However, the demarcation between green and dead tissues is sharp in Phomopsis-blighted seedlings and gradual in seedlings affected by drought. Damage from the lesser cornstalk borer can be distinguished from Phomopsis blight by the straw color of the dead tops and by the feeding wounds on the lower stem and taproot present in the former. Needle blight of junipers and other species in the Cupressaceae caused by Cercospora sequoiae Ell. & Ev. var. Juniperi Ell. & Ev. can be easily distinguished from Phomopsis blight. Cercospora infection starts on the oldest needles of lower branches and spreads upward and outward, while Phomopsis infection starts at or near the tips of the shoots.
Recently, Kabatina juniperi Schneider & v. Arx has become a problem in juniper outplantings and in production of grafted junipers. The fungus causes symptoms similar to those caused by Phomopsis. The tips of branches are killed for a short distance and the dark fruiting bodies (acervuli) develop on ashengray tissues, as is the case with Phomopsis. A specialist can recognize differences in spore size and fruiting bodies between this fungus and Phomopsis. The time of symptom development is also helpful in distinguishing between these two blights. Kabatina blight symptoms develop only when new growth begins in the spring, while Phomopsis blight symptoms develop anytime during the growing season.
Spores produced in fruiting bodies (pycnidia) formed on leaves and stems of seedlings infected the previous year are the most important source of inoculum early in the growing season. Pycnidia with viable spores may develop within 3 to 4 weeks after seedlings become infected, but usually are not well developed until infected tissues have dried considerably.
Figure 4. Pycnidia on leaves and branches.
|These spores are most commonly found on tissues that have turned ashen gray. The pycnidia are at first embedded in needles and stems, but partially erupt through the epidermis (fig. 4). Two types of spores (alpha and beta) develop in the same or different pycnidia (fig. 5) and are extruded in whitish tendrils. The fungus can produce spores for as long as 2 years in dead parts of infected plants.|
|Spores are dispersed primarily by rain splash. Infection is caused by alpha-spores; the filamentous betaspores do not germinate. Only a short period of high humidity is needed for infection to occur; for example, seedlings exposed to 100 percent relative humidity (24º C) for only 7 hours can become infected. Spore germination, germ-tube development, and infection are optimum near 24º C; however, disease development is enhanced by higher temperatures (32º C).||
Figure 5. Alpha and beta (long) spores of Phomopsis juniperovora.
|Figure 6. Eastern redcedars resistant to Phomopsis juniperovora adjacent to a severely infected juniper.||Control
Because susceptible new foliage and viable fungus spores are present throughout the growing season in juniper seedling beds, protective fungicides need to be applied regularly during this season. The only chemical currently registered for control of Phomopsis blight is benomyl. This chemical applied at 7- t 10-day intervals, combined with a vigorous schedule of roguing infected seedlings over the same interval, will give excellent control of Phomopsis blight.
|Other actions can be taken to reduce losses. Sowing juniper seed adjacent
to beds containing juniper stock should be avoided if possible. Poorly drained
areas should be avoided because losses are often greater where water tends to
stand. If overhead sprinklers are used, seedlings should be irrigated so that
water on seedlings dries before nightfall. Because shading frames increase the
length of time that moisture remains on foliage, they should not be used unless
absolutely necessary. Junipers or other hosts of this fungus should not be used
in nursery windbreaks or in landscape plantings on nursery grounds because they
may be a source of inoculum (spores) for nursery stock. Such trees are more
likely to be extensively infected if pruning results in the development of
There is considerable variation in susceptibility to Phomopsis juniperovora among junipers (fig. 6). Research is seeking to determine if there is genetic resistance to Phomopsis juniperovora among and within progenies from select eastern redcedar trees.
Hahn, Glenn Gardner. Taxonomy, distribution, and pathology of Phomopsis occulta and P. juniperovora. Mycol. 35: 112-129; 1943.
Hodges, C. S.; Green, H. J. Survival in the plantation of eastern redcedar seedlings infected with Phomopsis blight in the nursery. Plant Dis. Rep. 45: 134-136; 1961.
Otta, J. D. Benomyl and thiophanate methyl control Phomopsis blight of eastern redcedar in a nursery. Plant Dis. Rep. 58: 476-477;1974.
Otta, J. D. Alpha and beta spore occurrence in Phomopsis juniperovora pycnidia on Juniperus virginiana and in culture. Can. J. Bot. 56: 727-728; 1978.
Otta, J. D.; Fiedler, D. J.; Lengkeek, V. H. Effect of benomyl on Phomopsis juniperovora infection of Juniperus virginiana. Phytopathol. 70: 46-50; 1980.
Peterson, Glenn W. Cedar blight. In: Internationally dangerous forest tree diseases. Misc. Pub. 939. Washington, DC: U.S. Department of Agriculture; 1963: 105-106.
Peterson, Glenn W. Field survival and growth of Phomopsis-blighted and nonblighted eastern redcedar planting stock. Plant Dis. Rep. 49: 121-123; 1965.
Peterson, Glenn W. Chemical control of Phomopsis blight of junipers: a search for new methods. Tree Plant. Notes. 23(3): 3-4; 1972.
Peterson, Glenn W. Infection of Juniperus virginiana and J. scopulorum by Phomopsis juniperovora. Phytopathol. 63: 246-251;1973.
Peterson, Glenn W.; Sumner, D. R.; Norman, C. Control of Phomopsis blight of eastern redcedar seedlings. Plant Dis. Rep. 49: 529-531; 1965.
Peterson, Glenn W. Phomopsis blight of junipers. In: Forest Nursery Diseases in the United States. Agric. Handb. 470. Washington, DC: U.S. Department of Agriculture; 1975: 76-79.
Peterson, Glenn W.; Otta, J. D. Controlling Phomopsis blight of junipers. Am. Nurseryman 149(5): 15, 75, 78, 80-82; 1979.
Schoeneweiss, Donald F. Susceptibility of evergreen hosts to the juniper blight fungus, Phomopsis juniperovora, under epidemic conditions. J. Am. Soc. Hortic. Sci. 94(6): 609-611; 1969.
Smyly, W. B.; Filer, T. H., Jr. Benomyl controis Phomopsis blight on Arizona cypress in a nursery. Plant Dis. Rep. 57: 59-61; 1973.
|Revised October 1982|
Formatted for the Internet October 27, 1999
U.S. GOVERNMENT PRINTING OFFICE: 1982 - 378-632