Reports on Plant Diseases
RPD No. 622 - Phomopsis Twig Blight of Juniper
[ Symptoms ] [ Disease Cycle
] [ Cultural Control ] [ Chemical
Phomopsis twig blight of juniper, also known as nursery blight, cedar,
juniper, or needle blight, is caused by the fungus Phomopsis juniperovora.
Economic damage to landscape plantings and nursery stock is largely restricted
to species and cultivars of juniper (Juniperus). Other evergreens
that are attacked include arborvitae (Thuja), species of true cedar
(Cupressus), and false cedar (Chamaecyparis), European larch
(Larix decidua), jack pine (Pinus banksiana),
English yew (Taxus baccata), Japanese plum yew (Cephalotaxus
drupacea), Douglas fir (Pseudotsuga taxifolia), species
of fir (Abies), and Cryptomeria japonica. The disease is
mainly a leaf and shoot infection found in young plants and on the new
growth of older plants.
Click on image
for larger version
Phomopsis twig blight
on juniper shoot. Note
pycnidia of Phomopsis
fungus on stem.
Juniper seedlings and transplants in nurseries are highly susceptible and are
commonly killed by the blight. Overhead irrigation in a nursery is conducive
to infection, and a large number of seedlings, transplants, or grafts can be
blighted and killed in a very short time. The value of older nursery stock diminishes
markedly from infection and the survival of this stock is poor after planting.
The disease be-comes progressively less serious as trees and shrubs grow older,
even though the new growth of older plants is very susceptible, death or severe
damage to a plant over five years old is much less likely.
During prolonged wet, warm periods in spring and summer (April through early
June) and again in late August and September, the fungus becomes particularly
infectious. Phomopsis twig blight to juniper is found in most of the United
States–from the Pacific Northwest, throughout the Great Plains from South Dakota
to Texas, and eastward through the entire Midwest to the East Coast–as well
as in Canada, however, it is not common on plants growing in the wild.
on image for larger version
Figure 2. Phomopsis
the cause of Phomopsis blight
of junipers - seen under microscope.
(drawing L. Gray).
Yellow spots at the shoot tips of young needles are the first symptoms
to appear, although older needles may also show the spotting. As the infection
progresses from the needles into the stems, a gradual dieback of the new
shoot growth occurs changing from light yellow to red brown to ash gray,
eventually killing the entire branch.
Lesions occur on the stems and frequently develop into cankers at the
junction of healthy and diseased tissues. Small stems (less than 1/3 inch
in diameter) are usually girdled by these cankers, causing the stem tissue
beyond the cankers to die. Older branches (more than 1/3 inch in diameter)
are more resistant to infection, and cankers that form on them usually
heal. In advanced stages of infection, small black spots (the fungus fruiting
bodies or pycnidia) can be seen with the unaided eye or with a magnifying
glass on the dried, ash gray parts of stems and needles (Figure 1). The
central part of a plant is often more affected than its outer portion,
with the new growth showing almost continuous infection. Under certain
conditions favorable for fungal development, the entire shrub or tree
(especially a young plant) may be affected, and all its needles and stems
will die and turn brown.
Phomopsis twig blight is easily confused with four other problems of junipers:
Under drought conditions, the -tips of branches may be killed, but the
line of demar-cation between green and dead tissues is gradual, while in
Phomopsis blight, this line is sharp;
Damage from the lesser cornstalk borer (Elasmopalpus lignosellus)
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;
Another fungus, Cercospora sequoiae, causes a blight in junipers
and related species, but in this disease only the needles, not the stems
(as in Phomopsis blight), are infected. Also, infection by Cercospora
starts on the oldest needles of the lower branches, spreading upward and
outward, whereas infection by Phomopsis starts in newly developed
needles and progresses inward; and,
- A third fungus, Sclerophoma pythiophila, perfect state Sydowia
polyspora, causes a tip dieback with symptoms very similar to those of
Phomopsis. Sclerophoma attacks weakened or damaged juniper tips
in Illinois and Wisconsin, especially front-injured tips. The only way to
distinguish Phomopsis from Sclerophoma is through microscopic
examination of the pycnidia. The main difference between the two fungi is
in the spores that are produced within the pycnidia. Phomopsis produces
two distinct types of conidia, alpha and beta (Figure 2), while Sclerophoma
produces only alpha-type spores that do not have the two oil globules of Phomopsis.
Other hosts besides junipers in North America that have been reported as being
infected by Sclerophoma include Norway (Picea abies) and Engelmann
spruces (P. Engelmannii), numerous pines (Pinus spp.), Douglas
fir (Pseudotsuga menziesii), tamarack (Larix laricina), and
white fir (Abies concolor). Sclerophoma is considered a weak
pathogen on evergreens and associated with tissues injured by insects or unsuitable
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The most common sources of infection each spring are spores (conidia) produced
in fungal fruiting bodies (pycnidia) that appear as black spots on the needles
and stems infected the previous year (Figure 2). New pycnidia formed in the
current growing season are also a source of infective spores. The microscopic
spread by the wind, insects, and during pruning and other handling operations.
Under moderate temperatures (60 ° to 82° F or 15 ° to 27 ° C)
and high humidity, the spores germinate within seven hours after coming in contact
with young needles, especially those still in the yellowish green stage. After
the needles mature (develop a normal, deep green color), they are not susceptible
Germinated spores of Phomopsis are not killed by drying, like many other
fungi, but begin growing again when moist conditions return. Within three to
five days after infection, the fungus permeates the young needles and quickly
invades young stem tissue. After colonizing a side shoot, the fungus mycelium
progresses into the main stem, growing rapidly along the inner bark, killing
the cambium and staining the wood a brownish color.
Within three to four weeks after infection, pycnidia develop on the needles
and stems that have died and turned ash gray. At first, the pycnidia are embedded
in the tissue, but later, after the infected tissue has dried considerably,
they partially erupt through the epidermis. During wet, warm weather, spores
ooze from the pycnidia and are easily and quickly dispersed. The fungus can
persist as mycelium in dead parts of infected plants for as long as two years.
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- Plant only resistant species, varieties, and cultivars of junipers.
- Where practical, prune out and burn all blighted parts as they appear.
Restrict pruning or shearing to periods of dry weather. Infection can be further
reduced by restricting pruning to periods when the resulting new growth, stimulated
by pruning, occurs in the drier part of the season, which is from late June
through early August.
- In nursery operations:
- Every seven to ten days, in dry weather, remove and burn all infected
seedlings or place them in sealed plastic bags and haul them to a sanitary
- If possible, avoid having juniper seedbeds adjacent to beds containing
older junipers or other susceptible stock.
- Avoid planting in poorly drained areas.
- If overhead sprinklers must be used, irrigate seedling beds early in
the day to allow for drying before nightfall.
- Avoid using shading frames because these increase the length of time
that moisture remains on the foliage.
- Do not use junipers or other hosts as windbreaks or as landscape plantings
in or around a nursery because they may become a source of spores for nursery
- Avoid wounding trees when cultivating and transplanting them.
- Do not use branches or needles of junipers or susceptible plants for
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- In nurseries, apply a suggested fungicide to seedlings throughout the growing
season, beginning at seedling emergence. Weekly elimination of all infected
seedlings, and spraying with a fungicide every 7 to 10 days have been shown
to be very effective. Fungicide recommendations are given in Illinois Urban
Pest Management Handbook which is revised annually.
- For landscape plantings, fungicides give effective control when applied
at the right time. Since only new growth is susceptible, spray at budbreak
and then repeat at 10- to 14-day intervals until the new growth has matured
(when needles have changed from light yellow green to dark green). Spray also
when new flushes of growth appear in the summer and early fall, or in response
to pruning or shearing. If extended periods of wet weather persist, spray
every 10 to 14 days as long as young, susceptible needles are present.
- Because the fungus can only invade and attack young, tender, unwounded needles
of healthy, vigorous plants, keeping new growth thoroughly protected by regular
spraying is very important.
Contact Nancy R. Pataky, Extension Specialist and Director of the Plant
Disease Clinic, Department of Crop Sciences, University of Illinois at Urbana,
for further information on diseases of ornamental plants.
University of Illinois Extension provides equal
opportunities in programs and employment.
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