Pine Needles Turning Brown in Montana: How to Tell Why

Which needles are browning, and when did it start?

Start with three observations before you look anything up. First, position on the branch: needles close to the trunk are the oldest, and needles at the branch tips are this year's growth. Second, position on the tree: one side only, the lower branches, the top, or the whole crown at once. Third, the calendar, because several of these problems have a season.

Take a few dated photos from the same spot, too. If what you mostly want to know is whether the tree is dying, our guide to the 8 signs a tree is dying covers the wider checklist. This one stays with needles.

Is it just normal fall needle drop?

Often, yes. MSU Extension describes seasonal needle drop as the gradual yellowing or browning and eventual loss of older interior needles, occurring in late summer to early fall. How many years of needles a pine holds depends on the species. In MSU's description, Austrian and Scotch pines typically lose only their fourth-year needles, while white pines can yellow and drop third-year and even second-year needles throughout the tree, which looks dramatic and is still normal.

The test is simple. If the brown is on the inside of the branch, the tips are green, and it is September or October, MSU's guidance is that no management is necessary. Its one piece of advice for that season is to irrigate evergreens thoroughly before the ground freezes. What to do with the needles once they are on the ground is a separate question, and we cover it in our pine needle cleanup guide.

Why did it turn brown on one side in spring?

That is the usual signature of winter burn, which MSU Extension also calls winter injury or evergreen desiccation. Through a western Montana winter the needles keep losing moisture to sun and dry wind while the roots sit in frozen soil and cannot replace it. MSU's Schutter Diagnostic Lab reports that these symptoms can appear without warning in spring: red, yellow or brown foliage, especially at the needle tips, sometimes on entire branches, and more pronounced on the south and southwest sides. MSU's tree problem MontGuide adds the windward side to the places to look.

Exposure makes it worse. MSU lists high wind, large swings between day and night temperatures, little snow cover, and young or newly transplanted trees without established roots. The encouraging part is the buds. In MSU's words, as long as the buds are soft and green there is still good growth and life in the tree, and the damage becomes less obvious once new growth pushes and dead needles drop. So check the buds before you cut anything.

What does drought stress look like on a pine?

Drought browning tends to follow the sun, not the calendar. MSU Extension notes that drought stress is most apparent in the parts of the crown that are in full sun, and that it brings reduced growth and early needle drop, so a dry year can make an ordinary fall shed look far heavier than usual. Trees in the ground three years or less are the most likely to be permanently injured.

Drought matters for a second reason. MSU states that drought-stressed trees have decreased resistance to pests, which is how a dry summer can turn into a beetle problem the following year. The practical response is water, applied slowly and deeply, and our guide to watering trees through a Montana drought sets out how.

How do you tell bark beetles from everything else?

Look at the trunk, not the needles. With mountain pine beetle, MSU Extension describes needles turning reddish-brown along with boring dust beside the tree and pink, popcorn-like resin spots on the trunk. With pine engraver beetles, the Forest Service guide used by Montana DNRC describes reddish-orange boring dust in bark crevices, at branch junctions and around the base, and crowns that go light green or yellow within months of attack and fade to red later that year or the following spring.

Position helps too. Pine engravers often kill just the top of a larger pine, so a red top above a green lower crown points that way. In both cases the whole affected section changes color together, new needles and old, which is the opposite of fall shed. Our guides to the mountain pine beetle and to pine engraver beetles and slash go into each insect.

Could it be a needle disease?

Two fungal diseases are worth knowing by pattern. Dothistroma needle blight, per MSU Extension, shows up in late summer to fall as reddish-brown spots that widen into bands around the needle. The tip of the needle beyond the band turns brown while the base stays green, and infection is more severe on the lower branches. The spores infect two- to three-year-old needles during cool, wet weather.

Diplodia tip blight works at the other end of the branch. MSU describes current-year branch tips turning brown and dying, new needles that stay stunted, heavy resin on infected branches and symptoms that are worse low in the tree. It lists two- and three-needle pines such as Austrian, Scots and mugo among the hosts. MSU names fungicide options and timing for both diseases, and notes that fungicide will not cure needles already infected. Label directions are the law for any product, and some products require a licensed applicator.

What about salt, scale insects and weed killers?

Location answers the salt question. University of Wisconsin Extension, in the absence of a Montana fact sheet on the subject, describes de-icing salt injury as more severe on the side of the plant facing the road, decreasing with distance, and worst where runoff from salt-laden snow collects. A pine browning on its driveway side in spring could be winter burn or salt, and the two can stack.

Turn a few needles over as well. Pine needle scale appears as white coverings on the needles, and MSU notes that heavy infestations can cause yellowing and are often a sign of an already stressed tree. Finally, MSU Extension states that conifers as well as broadleaf trees are susceptible to drift from lawn weed killers such as 2,4-D and dicamba. If browning followed a spray day, see our guide to herbicide damage on trees.

Can a root problem turn the whole tree brown?

Yes, and it is the cause people check last because it is out of sight. When a whole pine thins and fades evenly with no beetle signs and no side-to-side pattern, look down. MSU Extension lists the lack of a trunk flare at the soil line as the most obvious sign of a tree planted too deep or buried by a grade change, and notes that most tree roots grow in the top six inches of soil. The Forest Service guide warns that more than four inches of soil or mulch over the roots stresses pines, and advises against backfilling or paving over root areas.

Too much water does similar harm. MSU's MontGuide describes continuously wet soil from poor drainage or excess irrigation damaging roots and cutting the tree's ability to take up water.

When should an arborist look at it?

Call when the browning is at the tips or the top, when a whole section changed color at once, when you see boring dust or resin on the trunk, or when the pattern is spreading. Those are the cases where timing changes the outcome, either for that tree or for the pines next to it. MSU's Schutter Diagnostic Lab also diagnoses plant disease, insect and environmental problems, and accepts photos by email before asking for a physical sample.

A tree health assessment puts an ISA Certified Arborist at the tree to read the pattern, check the trunk and root flare, and tell you whether the answer is water, pruning or removal. It is one of our core tree services, and the rest of the Montana Tree Guide covers the individual species and pests in more depth.

Call HJ Property Care & Tree Service at (406) 215-7319 or request a tree assessment and an ISA Certified Arborist will look at the tree with you.

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