Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001690
11/12/99
Twig Blight of Juniper
Twig blight of juniper is caused by Phomopsis juniperovora
Hahn, Cercospora sequoiae var. juniperi and Kabatina
juniperi Schn. & v. Arx. Twig blight of horizontal
varieties of juniper, particularly "blue rug" types, is a
common problem in Michigan. Phomopsis twig blight also
may cause a more rare dieback of branches of eastern red
cedar, arborvitae, taxus, fir, Douglas fir, larch,
cypress, jack pine, hemlock, true cedar and false cedar.
Symptoms include the dieback of the tips (Vis. 1) of
branches that are equal to or smaller in diameter than a
pencil. Infected foliage becomes pale, then reddish brown,
then turns brown or ash-gray after death. To confirm your
diagnosis of Phomopsis as the cause of twig blight, scrape
away the thin bark until you reach living wood. There
should be a sharp line between discolored dead wood and
healthy wood. Also, look at the base of the ash-gray
scale needles for small, black fruiting bodies. The
fruiting bodies form the spores that cause new infections.
In wet weather, spores ooze from the fruiting bodies and
splash onto new foliage. The spores are produced year
round and infect yellowish-green juvenile foliage. The
darker green mature foliage is resistant to infection.
Junipers generally have two flushes of growth under natural
conditions, one in spring and another in summer. When new
growth coincides with wet, warm weather or frequent overhead
sprinkler irrigation, disease can become severe. Pruning,
which stimulates the formation of new growth, can increase
the severity of the disease by providing flushes of juvenile
foliage susceptible to infection. Most severely diseased
plantings are the result of excessive wetness, usually from
being planted in poorly drained, shaded and over-watered
areas. Under continuously wet conditions, an entire plant
may die.
Two other fungi can cause twig blight in juniper:
Cercospora sequoiae var. juniperi and Kabatina juniperi
Schn. & v. Arx. The distribution and severity of the two
diseases is not yet known. The symptoms are identical
for the Phomopsis and Kabatina twig blights, but the
Cercospora twig blight is different.
The Cercospora infections start on the oldest foliage on
lower branches and the blight spreads upward. The branch
tips usually remain healthy and green. Early symptoms
occur on the leaves of the spur branches. The leaves brown
at the tip, then become entirely brown and die. This
foliage usually dies in late summer and the affected spur
branchlets fall off in the fall, leaving a plant with an
inner crown devoid of foliage. On the infected brown
leaves, small, dark fruiting bodies form and produce the
spores that cause new infections of the previous years'
spur leaves. Wet weather is needed for spores to infect
foliage, and the longer foliage remains wet, the more
disease develops. The spores are produced from spring
through fall, but most infection occurs in summer in some
years and in late summer other years.
Cercospora twig blight is most destructive on Juniperus
scopulorum and J. monosperma and seldom causes problems in
J. virginiana in the landscape. On nursery seedlings,
the disease is usually seen only on the grafted
selections.
Control: Avoid over-watering and planting in poorly
drained or shaded locations. Plant resistant varieties
and cultivars. Resistance to twig blight is influenced by
the provenance. Thus, cultivars listed as resistant in
other states may be susceptible in Michigan. Fungicides
may be needed. To control Phomopsis twig blight, spray a
fungicide at 10 to 14-day intervals when new flushes of
growth occur until new growth has matured to a dark green
color. To control Cercospora twig blight, apply a very
persistent fungicide about late June or early July.
This information is for educational purposes only. References
to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU
Extension. Reprinting cannot be used to endorse or advertise
a commercial product or company.
This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
For more information about this data base or its contents please contact
heatley@msue.msu.edu . Please read our
disclaimer for important
information about using our site.