8 Signs a Tree Is Dying Slowly, and What Is Behind It

What usually kills trees in Montana?

Stress, more than pests. MSU Extension puts physiological stress, meaning drought, winter injury, poor planting and root damage, ahead of disease and insects as the biggest threat to ornamental trees in Montana. Insects and diseases tend to finish off trees that stress has already weakened. So most of the signs below are symptoms, and the useful question for each is what stressed the tree in the first place.

1. Dieback from the top and the outside in

Bare twigs at the top of the crown and the ends of branches, spreading inward year by year, is the classic pattern of a tree that cannot supply its whole canopy. On spruce, MSU notes drought injury usually progresses from the top down and the outside in, and can keep developing for several years after the dry spell ends. On pines and spruce, sudden top dieback with boring dust at the base can also mean Ips engraver beetles.

2. A thinner canopy, smaller leaves and short new growth

Compare this year's canopy with photos from a few years ago. Fewer and smaller leaves, and shorter growth between buds, are among the drought-stress symptoms MSU lists, and they often show a year or two before any branch actually dies.

3. Scorched leaf edges, early fall color or early drop

Leaves browning from the tip and margins inward, changing color in August, or dropping early all point to water stress. MSU names aspen, maple, ash, oak, linden and birch as the most susceptible to leaf scorch, and notes that low soil moisture over winter and spring contributes, not just summer heat.

4. Browning needles on evergreens

Three causes look similar. Winter desiccation shows up in spring as brown needle tips, worst on the south and southwest side, because winter sun and wind dried the needles while the roots sat in frozen soil. Rhizosphaera needle cast browns the older inner needles of spruce while the tips stay green. Dothistroma needle blight bands ponderosa and Austrian pine needles with reddish-brown spots in late summer and fall. One is a watering problem and two are diseases, so it is worth getting the cause right.

5. Cankers, oozing and dead patches of bark

Sunken, discolored areas of bark, sometimes with black pimple-like spots or orange threads in wet weather, are often Cytospora canker, which MSU says mainly attacks stressed trees. On spruce it shows as whitish-blue resin on the bark and branches dying in a spiral from the bottom up. On aspen and cottonwood the bark may ooze. Pruning out cankered branches helps; fixing the stress helps more.

6. Pitch tubes, boring dust or small exit holes

On pines, pink popcorn-like blobs of resin on the trunk and sawdust at the base mean mountain pine beetle, and needles on an infested tree turn reddish-brown. MSU is blunt that once beetles are in, the tree is unlikely to survive; protection is preventive only. On birch, D-shaped exit holes and raised bark ridges mean bronze birch borer, which also targets stressed trees. See our mountain pine beetle guide.

7. No root flare, girdling roots or a burst of suckers

A trunk that goes straight into the ground like a pole, with no flare, usually means the tree was planted too deep or had soil piled over its roots. MSU links deep planting to weak growth, early leaf drop, scorch and girdling roots, and calls improper planting a major reason trees die early. A sudden burst of suckers from the base can be a sign of winter root damage. Root problems also follow construction: Colorado State notes that trenching, compaction and grade changes can cause decline that appears gradually over several years.

8. Wilting and yellowing high in an elm in summer

On American and European elms, leaves in the upper canopy that curl, wilt and turn yellow or gray-green in summer, a pattern called flagging, with brown streaks in the wood under the bark, are the signature of Dutch elm disease. It has been documented in urban areas across Montana. Infected elms should be assessed quickly, because the disease spreads through bark beetles and root grafts to neighboring elms.

How can you tell if a branch is still alive?

Use a scratch test. With a fingernail or pocketknife, scrape a small patch of bark on a twig: green, moist tissue underneath is alive, and dry, brown tissue is not. Start near the base of the branch and work outward to find where live wood ends. Live twigs also bend, while dead ones snap. Do this in late spring, after leaf-out, so you are not confusing dormancy with death.

Can a declining tree be saved?

Often, if the cause is found early and it is one you can change. Deep watering through dry spells and before the ground freezes, mulch over the root zone, correcting a buried root flare, and pruning out dead and cankered wood all help a stressed tree recover. Bark beetles in a pine and Dutch elm disease in an elm are the main exceptions, where removal is usually the answer. An arborist's tree health and risk assessment will tell you which you are dealing with.

If you would like a second set of eyes on a tree, contact us, or compare local arborists in our lists of the best tree services in Missoula and the Bitterroot Valley.

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