Plant Disease & Problem Library

Evergreen Needles Browning or Dropping

This is our most common call, and the most misdiagnosed. Six different problems turn a spruce or arborvitae brown, and they look nearly identical from your driveway — but two of them are treatable, two will grow out on their own, and two mean no amount of spraying will help. Finding out which one you have is the entire ballgame.

Needle Cast (Rhizosphaera)

Classic on Colorado blue spruce: browning and purpling starts on inner, lower branches and works outward and upward over years. Infected needles drop, leaving bare interior branches. Fungal, and treatable — but timing matters, and recovery takes multiple seasons because spruce won't regrow needles on bare wood.

Spruce Spider Mites

Needles look dull, stippled, or bronzed rather than cleanly brown, often with fine webbing at the base. Worst in hot, dry stretches. Hold white paper under a branch and tap — moving specks confirm it. Frequently misdiagnosed as disease and sprayed with fungicide, which does nothing.

Bagworms

Those "pine cones" hanging off your arborvitae or spruce are caterpillar cases, and each one holds hundreds of eggs. They can strip and kill an arborvitae in a season or two. Timing is everything — treatment works on young larvae in early summer and is nearly useless once the bags seal in late summer.

Root & Planting Problems

Planted too deep, girdling roots, wire baskets left on, soil piled against the trunk, compaction, or drought stress. The tree browns from general decline rather than in a disease pattern. No spray fixes this — and this is why we diagnose before we quote.

Winter Burn & Desiccation

Browning on the windward or sun-exposed side, appearing in late winter or early spring on arborvitae, boxwood, holly, and rhododendron. The plant lost moisture it couldn't replace from frozen ground. Cosmetic damage that often grows out — worth waiting before anyone treats anything.

Deer Browse

Not a disease at all: clean-stripped lower branches with a distinct browse line, worst on arborvitae and yews in winter. Ragged torn ends rather than clean cuts, since deer have no upper front teeth. See deer damage repair & prevention.

Leaves Chewed, Skeletonized, or Stripped

Watching something eat a plant you paid for is maddening, but hold on before you spray. A healthy tree shrugs off losing a share of its leaves in one season — that's normal, and the birds are usually handling it. The ones worth acting on are the pests that come back with reinforcements or kill outright, like bagworms on an arborvitae hedge.

Sawflies

Caterpillar-lookalikes feeding shoulder-to-shoulder in groups, stripping pine, spruce, and roses fast. They're not caterpillars (they're wasp relatives), which matters: Bt — the go-to organic caterpillar product — does nothing to them.

Japanese Beetles

Leaves reduced to lace with the veins left behind, on roses, lindens, cherries, and birch every July. The adults you're swatting are the second act — the first was grubs in your lawn. See our Japanese beetle guide.

Bagworms

Listed under evergreens above because that's where they do the most damage in Central PA, but they'll also work deciduous trees. Look for the hanging cases before you look for the caterpillar.

Caterpillars & Leaf Rollers

Chewed margins, rolled or tied leaves, webbing at branch tips. Most are cosmetic on a healthy tree and genuinely don't need treatment — we'll tell you when that's the case rather than sell you a spray.

Deer & Rabbits

Whole shoots gone rather than leaf damage. Rabbits cut cleanly at a 45-degree angle low to the ground; deer tear raggedly and reach higher. See deer damage.

Branch Dieback, Trunk Damage & Whole-Plant Decline

This is the serious category. When whole limbs die back or a tree declines year over year, the clock is real and some of these have no cure. It's also where you most want an honest opinion before spending money — we would rather tell you a tree is finished than sell you three years of treatments on it.

Borers

Small round or D-shaped exit holes, sawdust-like frass, sap bleeding, and branches dying from the top down. Emerald ash borer has effectively ended untreated ash in our area. Borers usually target already-stressed trees — which means the borer is often the symptom, not the disease.

Canker Diseases

Sunken, discolored, sometimes oozing areas on branches or trunk, with everything beyond the canker dying. Cytospora canker on spruce is extremely common in Central PA landscapes. No spray cures canker — management is pruning, and correcting the stress that let it in.

Verticillium Wilt

One side or one limb wilts and browns while the rest looks fine; cut wood shows dark streaking. Soil-borne, and it hits maple, redbud, catalpa, and smoke bush. There's no cure — knowing that saves you from paying for treatments that can't work, and changes what you replant.

Rootstock Suckers

Vigorous shoots from below the graft on flowering cherries, crabapples, and roses — different leaves, different growth rate, and they'll take over the tree if left. Not a disease; a pruning issue with a deadline. See the full explanation.

Girdling Roots & Planting Depth

A trunk that enters the soil like a telephone pole with no visible root flare is strangling itself. Causes slow, unexplained decline over years and gets misdiagnosed as everything else. Correctable when caught early enough.

Storm & Mechanical Damage

Torn limbs, split crotches, string-trimmer wounds at the base, and lightning strikes — all entry points for canker and borers. See our guide to storm-damaged trees and shrubs.

Diagnosis FAQ