Pathological
Disorders –
Shoot Blights
Shoot blights on junipers (red cedar) and blight on
arborvitae may affect new needles, twigs or smaller
branches. Affected plant parts
(82KB color jpg) turn light brown
to reddish brown and later may turn ashen gray. Blight
symptoms can be confused with damage from drought, the
lesser cornstalk borer or rodent damage.
Thuja blight on arborvitae (Thuja sp.), caused
by the fungus Pestalotia, is seldom serious except
where arbovitae is grown under crowded or dark conditions
such as under dense shade of other trees or crowded among
other conifers. Lower branches damaged by snow, ice or
animal urine seem to be favorable for infection.
Juniper blight can be caused by one of three fungi: Phomopsis,
Cercospora or Kabatina. A laboratory diagnosis
is needed to confirm which blight pathogen is present.
Cercospora blight affects only the needles of eastern
red cedar and Rocky Mountain juniper. Infection starts on
the oldest needles on lower branches and spreads upward
and outward. Infection occurs in early summer. Needles
die by late summer and drop by mid-fall. Severely
affected trees have tufts of foliage only on branch tips.
Trees may be killed. Control is possible with two
properly timed applications of fungicide.
Blight caused by Phomopsis
(68KB color jpg) or Kabatina (51KB color jpg) may involve shoots and
branches as well as foliage, so entire branch tips often
die. Foliage on affected shoots often turns
reddish-brown. Tiny black fruiting bodies form on killed
shoots. Microscopic examination of the spores from these
bodies is necessary for proper identification. Control of
Juniper and Thuja blights:
The following hardy juniper cultivars have been
reported resistant to Phomopsis blight: Juniperus
chinensis `Iowa', `Pfitzerana Aurea'; J. communis
cvs., `Repanda', var. depressa; and `Depressa Aurea', J.
procumbens; J. sabina, all cultivars; and J.
scopulorum `Silver King'. Other cultivars and species
also show resistance but may not be reliably hardy in
North Dakota. Varieties resistant to Phomopsis blight may
not be resistant to Cercospora or Kabatina.
Keep the trees growing steadily. Prune and dispose of
all blighted parts when the plants are dry. Avoid
wounding when transplanting or cultivating. Space the
plants for good air circulation and avoid overhead
sprinkling. Under nursery
conditions (82KB color jpg),
destroy infected plants and apply fungicide at one week
intervals during periods of active growth in late spring
and late summer and fall according to label directions.
DIPLODIA TIP BLIGHT of two and three needle
pines, caused by the fungus Sphaeropsis sapinea,
has greatly increased in many parts of the United States
in recent years to become one of the most serious and
devastating diseases of planted pines In other states,
Austrian pine and Japanese black pine are the most
seriously damaged. In the Great Plains, Diplodia (67KB
color jpg) can be severe on Scots and ponderosa
pines as well.
Symptoms
Before symptoms appear, Diplodia has usually reached high
levels in the tree. This fungus infects the cones where
it develops minute black pyonidia which appear as raised
pimples on the cone scales (63KB color jpg). Spores are produced in
these which spread the infection. Once many cones on the
tree are infected, massive spore release can cause severe
infection of needles and shoots. It is this `tip blight' (48KB
color jpg) which causes the real damage and which
is so conspicuous. While spores are released from
pycnidia all through the season, most of the infection
occurs during expansion of the new shoots following bud
break. The fungus invades and kills growing shoots which
then turn brown (50KB
color jpg). Usually the older needles on the
branch remain alive. Shoots are often killed just as buds
expand so that the needles are only partly extended. The
brown, partly-extended needles remain attached to the
shoot tip. Shoots killed by Diplodia become resin soaked;
this is one distinguishing symptom of this disease. Often
the fungus fruits on the partly-expanded needles on
killed shoot tips. If such needles are pulled from the
sheath, the minute black pycnidia of Diplodia may be seen
on the needle bases.
The blight begins with a few shoots on lower branches
and moves throughout the tree. EventualIy many of the new
shoots may be killed. Diplodia blighted trees are so
disfigured as to lose much of their landscape or
ornamental value. Loss of most of the lower branches also
reduces the value of pines as wind breaks. In North
Dakota, where pines are already under severe climatic
stress, the loss of a significant proportion of new
shoots may result in death of the trees. Because the
fungus builds up on cones first, tip blight on windbreak
and landscape trees usually does not appear until the
trees reach reproductive age, usually 20 to 30 years.
Severe damage can develop in nurseries and on young trees
when infected older trees are nearby.
Symptoms can be confused with frost damage or tip moth
damage.
Control:
Stressed trees are more susceptible to tip blight;
maintain good fertility and water trees during droughts.
Avoid overcrowding in new plantings; give trees room to
develop. Do not plant young trees near old trees.
Pruning of blight-killed shoots will improve the
tree's appearance but will not stop the spread because
the spores for new infections are coming from the cones.
Picking off all mature cones is a tedious but effective
measure that will reduce the disease.
Because the period of peak susceptibility and
infection is short, it is possible to protect new growth
with fungicide sprays. Spray two or three times at weekly
intervals beginning as buds begin to swell (late April to
mid May).
Two other important shoot blights of pines are found
in adjacent states. Both are most serious on young
plantings.
Red Pine Shoot blight is caused by
the fungus Sirococcus strobilinus. The disease
causes death of new shoots soon after expansion. Young
infected shoots may bend over as they die forming
characteristic `shepherd's crooks'. Dead needles on older
shoots droop downward from the shoot. Older parts of
branches are seldom killed.
Scleroderris canker is wide-spread in
the north central states but has not been reported from
North Dakota. The needles on affected branch tips first
turn orange-brown at the base while the tips remain
green. Later all the needles turn brown. Current year's
needles are affected first; often older season's needles
remain unaffected until the canker girdles the stem.
Needles on infected shoots tend to fold back along the
stem. The wood under the bark shows a distinct greenish
coloration. A laboratory diagnosis is needed to
positively identify either of these shoot blights.
B A C K | N E X T | C
O N T E N T S
Environmental
Injury
Pathological Disorders - Foliage
Diseases
Pathological Disorders - Branch and
Stem Diseases
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