Common Issues with Conifer Trees in Montana - MSU Extension
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Common Issues
C
onifers are a staple tree in many landscapes,
but they can be affected by diseases and
arthropod-related issues, resulting in
with Conifer Trees needle discoloration, loss, and dieback of
branches. Additionally, most conifer issues are not due to
an insect or disease. Instead, many symptoms result from
in Montana growing conditions or weather. In other cases, growth is
normal but may look different than expected.
Bruce Watt, University of Maine, Bugwood.org
SPRING ABIOTIC DISORDERS OF CONIFERS
Winter Injury
This injury happens when there is minimal snow
cover and low humidity over the winter, causing conifers
to dry out. Symptoms include red, yellow or brown needle
discoloration appearing in the spring, especially on needle
tips. Damage is most obvious on south and southwest sides
of the tree. Water thoroughly during dry periods during the
growing season and into the fall to avoid this issue.
MSUEXTENSION.ORG / SUMMER 2021 / 29
Cytospora Canker
White Pine Weevil
Stigmina needle cast
30 / LIVES & LANDSCAPES / SUMMER 2021
Ips Bark Beetles
Rhizosphaera needle cast
Seasonal needle drop
Spruce Spider Mite
(top row, left to right) Eva Grimme; S. Katovich, Bugwood.org; Ward Strong, BC Ministry of Forests, Bugwood.org; (center row, left to right) Laurie Kerzicnik; USDA Forest Service - North Central Research Station, Bugwood.org
(bottom row, left to right) Joseph OBrien, USDA Forest Service, Bugwood.org; Eva Grimme
Seasonal Needle Drop Recommendations: Prune out and de- needle drop can occur. Damage is usually
Did you know that conifers naturally stroy affected branches. Support tree vigor concentrated on the older, inside needles in
shed some of their needles every year? In by providing adequate water and nutrients. the lower portions of the tree.
the fall you might notice interior needles Fungicides are not recommended. Recommendations: Reduce environmen-
turning yellow, and these usually turn brown tal stress to the tree and provide adequate
and fall off in the winter. A few trees might Pine Diseases (primarily Austrian, water. Several oils and miticides are available
have interior brown needles that hang on ponderosa, mugo) for spider mite control.
until spring. Dothistroma needle blight: Tan or
brown needle tips (often with a distinct Ips Bark Beetles (and close relatives)
Normal Plant Growth interface between dead and live tissue) that (pine and spruce):
Sometimes the way trees normally start as dark-green (water-soaked), tan or Ips beetles cause fading of needles and
grow can look surprising to a homeowner. reddish-brown spots, eventually forming eventual dieback on branches or tops of trees
For example, if a conifer has more pollen a band (possibly with small resin drops) (can also be confused with abiotic-related is-
cones than usual it might cause a second around needles; dark fruiting bodies emerge sues). Trees that are newly transplanted, have
look. Another example is certain trees with from needles. root injuries, or are stressed are more sus-
a characteristic like shredding bark. Recommendations: Remove fallen ceptible to Ips beetle attacks. Woodpeckers
needles. In spring, consider applying a might be seen feeding on the immature
COMMON DISEASES OF CONIFERS protectant fungicide once when new needles beetles underneath the bark.
Spruce Diseases are half their mature length and once when Recommendations: Terminal flagging
Needle Cast Diseases: Brown, bronze, fully grown. or dieback in the upper canopy requires a
or dark purple discoloration and gradual loss sample taken from this area of the tree to
of innermost needles. Symptoms often start COMMON ARTHROPOD ISSUES ON rule out bark beetle-related causes. It is hard
on lower branches. Youngest needles usually CONIFERS (if not impossible) to kill the beetles and
stay green. White Pine Weevil (spruce): correct damage once they are present in the
• Rhizosphaera needle cast: Small, The top of the tree (terminal) will wilt tree. Preventive contact insecticides can be
black, spherical fruiting bodies emerge and eventually die. Side branches will start sprayed on the trunk of trees that are not
from stomata. to grow upward to replace the dead leader. infested. Slash from infested trees should
• Stigmina needle cast: Small, black, Recommendations: The infested terminal be piled and burned prior to adult beetle
fuzzy-looking fruiting bodies emerge can be clipped, and a new leader can be emergence in May.
from stomata. trained (before July). Contact insecticides
• Sudden needle drop: Small, spherical, can be sprayed at the terminal of the tree or Eva Grimme is an Associate Extension
fruiting bodies form only on branches a systemic insecticide can be applied as a soil Specialist & Plant Disease Diagnostician.
or needle pegs. drench in the spring. Laurie Kerzicnik is an Associate Extension
Specialist and Insect Diagnostician. Noelle
Recommendations: Remove and destroy Western Spruce Budworm (Douglas-fir, Orloff is an Associate Extension Specialist
affected branches and fallen needles. Provide fir, spruce, and larch): and Plant Identification Diagnostician.
supplemental water during dry periods. Several areas of the tree will be defoliat-
Avoid spraying the needles with water ed. Needles will be deformed with chewing
during sprinkler irrigation. In severe cases, damage, insect excrement, and webbing.
consider applying a protectant fungicide in Recommendations: Beneficial predators
spring, once when new needles are half their help to control populations. Several contact
mature length and once when fully grown. insecticides are available for caterpillar control.
Treatments for two consecutive years are
recommended. Spruce Spider Mite (spruce, fir, pine,
Cytospora Canker: Canker develop juniper, arborvitae, Douglas-fir, and
on branches and/or trunks of stressed trees yew):
and may girdle limbs from within. Bluish or Needles will have a greyish hue with
whitish resin might be visible on the branches. flecking spots. Stunting and premature
MSUEXTENSION.ORG / SUMMER 2021 / 31
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