Conifer Diseases
9. Passalora Blight
Charles S. Hodges and Michelle M. Cram
Hosts Diagnosis 50 to 115 microns in diameter for P. se
quoiae and 60 to 200 microns in diameter
Passalora blight (Cercospora blight), Seedling foliage with Passalora blight for P. juniperi. Yellow-brown to brown
caused by Passalora sequoiae (syn. becomes brown along the stem and on the conidiophores protrude from the stromata,
Cercospora sequoiae), is associated with lower branches. The disease continues to forming a compact layer over the surface.
several members of the cypress family develop upward and outward until only The conidiophores are geniculate (bent
(Juniperus, Cupressus, Chamaecyparis, the upper branch tips remain green on abruptly; knee shape) and are 50 to 125
Thuja, Cryptomeria) and the bald cypress severely infected seedlings (fig. 9.1). by 4 to 6 microns for P. sequoiae and 20
family (Taxodium, Sequoia, Sequoiaden This damage pattern differentiates to 45 by 3 to 5 microns for P. juniperi
dron). Nursery seedling infection by Passalora blight from the more common (fig. 9. 2). The two fungi can be distin
P. sequoiae has been reported on eastern Phomopsis blight on juniper (see chapter guished by their conidial characteristics.
redcedar, giant sequoia, cypress, and bald 12) where the disease develops from the P. sequoiae spores are yellow-brown,
cypress. A similar disease on cypress and tips of the branches inward. cylindrical, slightly tapering, mostly 5 to
junipers, also commonly known as Pas 6 septate, echinulate (prickles) and aver
The fruiting structures of both fungi
salora blight, is caused by Pseudocerco age 40.5 by 5.4 microns (fig. 9.3). P. ju
are very similar. Dark brown pustule-like
spora juniperi (syn. Cercospora sequoiae niperi spores are olive-brown, cylindrical,
structures, or stromata, develop on needles
var. juniperi). mostly 5 to 6 septate, slightly echinulate,
shortly after they turn brown, and are easily
visible with a hand lens. The stromata are and average 40.8 by 3.1 microns.
Distribution
Both fungi that produce Passa
lora blight have wide distribution in the
Southern and Midwestern United States.
P. sequoiae also has been reported from
the West Coast and Hawaii.
Damage
Damage to seedlings in the nursery
by both fungi varies from very light to
almost complete defoliation. In southern
forest nurseries, P. sequoiae has caused
serious damage to eastern redcedar; while
in the North Central States, P. juniperi
has been a more significant problem on
Rocky Mountain juniper in windbreaks
and other plantings. No information is
available on infected seedling survival
and growth rates after outplanting; how-
ever, Passalora blight is likely to continue to
develop in the field on seedlings infected
in the nursery. The danger of introduc
ing the fungus into new areas exists if
infected seedlings are outplanted.
Figure 9.1—Passalora blight symptoms on eastern redcedar. Photo courtesy of the University of Wisconsin.
50 Forest Nursery Pests
Conifer Diseases
9. Passalora Blight
P. juniperi than Rocky Mountain juniper.
If available, use seed sources resistant to
Passalora blight.
Cultural
Use irrigation early in the morning
to promote rapid drying of foliage. After
a disease outbreak or lifting, incorporate
residual seedlings and debris into the soil
to reduce spring inoculum.
Chemical
Fungicides labeled for use in forest
nurseries against leaf or needle diseases
on conifers can be used to reduce infec
tion and spread of Passalora blight. A
standard spray schedule may be necessary
Figure 9.2—Conidiophores of Passalora sequoiae. Photo by Charles S. Hodges. throughout the growing season to control
this disease in some areas.
Biology structures that overwintered on needles
Initial infection of first-year nursery
of infected trees or seedlings. Disease Selected References
symptoms develop within 2 to 3 weeks,
seedlings usually comes from older and fruiting bodies form after the foliage
Crous, P.W.; Braun, U. 2003. Mycosphaerella
infected plants in the nursery or from and its anamorphs: names published in Cerco-
turns brown. The resulting conidia are spora and Passalora. Utrecht, The Netherlands:
infected nearby windbreaks or landscape spread primarily by wind. Production Centraalbureau voor Schimmelcultures. 571 p.
plantings of susceptible hosts. Spring of conidia and new infections can occur
inoculum is produced from fungal throughout the spring and summer. Wet Hodges, C.S. 1962. Comparison of four simi
lar fungi from Juniperus and related conifers.
weather and moderate temperatures favor
Mycologia. 54: 62–69.
disease development.
Hodges, Jr., C.S.; Peterson, G.W. 1989.
Cercospora blight of Juniper. In: Cordell, C.E.;
Control Anderson, R.A.; Hoffard, W.H.; Landis, T.D.;
Smith, Jr., R.S.; Toko, H.V., tech. coords.
Prevention Forest nursery pests. Agriculture Handbook
680. Washington, DC: USDA Forest Service:
Do not use known hosts of the two 29–30.
fungi as windbreak or landscape plants in
Peterson, G.W. 1977. Epidemiology and
or near the nursery. If known-host plants
control of a blight of Juniperus virginiana
are present, remove any that are infected.
caused by Cercospora sequoiae var. juniperi.
Variation in resistance to P. juniperi Phytopathology. 67: 234–238.
among genotypes of eastern redcedar
and Rocky Mountain juniper has been Zhang, J.W.; Klopfenstein, N.B.; Peterson, G.W.
1997. Genetic variation in disease resistance of
reported. In general, eastern redcedar has
Figure 9.3—Conidia of Passalora sequoiae. Photo by Juniperus virginiana and J. scopulorum grown
Charles S. Hodges. been found to be more resistant to in eastern Nebraska. Silvae Genetica. 46: l–16.
Forest Nursery Pests 51
