Green Mountain is a tough, slow-growing evergreen, but it shows stress plainly in its leaves. A change in color or shape is usually the first clue to what’s wrong. The same browning can mean a harmless winter tint or a disease that kills the plant, so figuring out the cause comes before any spray or pruning. Most lasting fixes come down to where and how the shrub is grown, not to chemicals.
Bronze or Orange Leaves in Winter
Many boxwoods turn bronze, orange or yellowish in winter as a normal response to cold and sun exposure, and how much they change depends on the variety.1Arboriculture & Urban Forestry. Evaluation of Winter Color Change in 40 Boxwood Cultivars and the Effects of Shade and Fertilization Plants in full winter sun usually tint more than shaded ones. Extra fertilizer does not prevent or reverse the color change.2Arboriculture & Urban Forestry. Evaluation of Winter Color Change in 40 Boxwood Cultivars and the Effects of Shade and Fertilization
Seasonal bronzing is even across the sunny face of the shrub, and the leaves stay firm. In spring, new growth comes in green. Patchy browning, dead stems or dropped leaves point to the problems in later sections. If you’re unsure whether a branch is alive, scratch the bark of a stem: green tissue underneath means it is.
Water deeply in fall before the ground freezes so the leaves go into winter hydrated. A burlap screen on the sunny or windy side cuts down winter sun and wind exposure.
Yellow to orange leaf tips and edges can also signal a nutrient deficiency.3Cornell Cooperative Extension. Photographic Guide of Boxwood Pests & Diseases on Long Island If the color stays into summer or the new growth is pale, test the soil before you fertilize.4Cornell Cooperative Extension. Photographic Guide of Boxwood Pests & Diseases on Long Island Keep soil pH from dropping below 5.5 to avoid nutrition problems; boxwood is often said to prefer about 6.0 to 7.2.5Cornell Cooperative Extension. Photographic Guide of Boxwood Pests & Diseases on Long Island
Wilting and Fading From Root Rot
The first sign of root rot is often a loss of shine across the whole shrub.6Cornell Cooperative Extension. Photographic Guide of Boxwood Pests & Diseases on Long Island Then the leaves wilt and turn light green, then tan, straw-colored or purplish brown, then dry out and drop.7Cornell Cooperative Extension. Photographic Guide of Boxwood Pests & Diseases on Long Island8LSU AgCenter. Boxwood Crown and Root Rot Infected roots are soft and brown, and their outer layer slides off when handled, leaving thin “rattail” roots.9Cornell Cooperative Extension. Photographic Guide of Boxwood Pests & Diseases on Long Island10LSU AgCenter. Boxwood Crown and Root Rot Damaged roots can no longer take up water or nutrients.11LSU AgCenter. Boxwood Crown and Root Rot The cause is a water mold, and it will kill infected boxwood.12Cornell Cooperative Extension. Photographic Guide of Boxwood Pests & Diseases on Long Island
You can check the roots yourself. Dig gently at the edge of the root ball and pull out a few fine roots. Healthy ones are firm and pale, while rotted ones are brown and mushy. Look at the base of the trunk for loose bark or a sunken area at the soil line, and notice whether the hole fills with water or the soil smells sour.
Water molds thrive in wet soil, and poor drainage and compaction make roots vulnerable.13Cornell Cooperative Extension. Photographic Guide of Boxwood Pests & Diseases on Long Island14LSU AgCenter. Boxwood Crown and Root Rot All varieties are less likely to be infected in well-drained soil.15Cornell Cooperative Extension. Photographic Guide of Boxwood Pests & Diseases on Long Island Avoid heavy soil, deep planting and overwatering, and use raised beds or containers if drainage is poor.16Cornell Cooperative Extension. Photographic Guide of Boxwood Pests & Diseases on Long Island If you amend heavy soil with compost, do it across the whole area the roots will reach, not just the planting hole.17University of Maryland Extension. Common Green Mountain Boxwood Problems and How to Fix Them
Once rot is confirmed, a badly affected shrub rarely recovers, so remove it with its roots. Don’t replant boxwood in the same wet spot until drainage is fixed. Nursery fungicides are mainly used to protect healthy plants, not to cure dying ones. A lightly affected shrub may hang on if you cut back watering and improve drainage.
Blistered Leaves From Boxwood Leafminer
Leafminer eggs hatch in early summer, and the larvae then live and feed inside the leaf for 9 to 10 months.18NewGen® Boxwood. Boxwood Leafminer That’s why the blisters are most obvious from winter to early spring, as pimple-like bumps.19NewGen® Boxwood. Boxwood Leafminer A single leaf can hold 10 or more larvae.20NewGen® Boxwood. Boxwood Leafminer In late April the larvae turn into pupae, and the small adult flies emerge and start a new cycle.21NewGen® Boxwood. Boxwood Leafminer
To confirm leafminer, hold a leaf to the light or peel it open and look for orange larvae inside. In May, small orange flies swarming around the shrub are the adults. Heavily mined leaves yellow and drop, which thins the shrub over time.
A blister is a hollowed-out patch of leaf, and it stays after the larva inside has died or left, so old blisters don’t prove the pest is still active. Cutting open a few blistered leaves in late winter or spring shows whether live larvae remain or only empty chambers. Because the damage lasts, judge a treatment by whether new growth stays clean the next year, not by whether old leaves look better.
Contact sprays work against the adult flies when they emerge, around mid-May to early June; confirm the pest is present before spraying.22Center for Agriculture, Food, and the Environment at UMass Amherst. Boxwood Leafminer: Landscape: Center for Agriculture, Food, and the Environment (CAFE) at UMass Amherst Sprays applied when the adults first appear can cut leafminer numbers by more than 85%.23Arboriculture & Urban Forestry (AUF). Application of Systemic Insecticides in Relation to Boxwood Leafminer’s Life History Systemic insecticides, products the plant absorbs, can be applied as a soil drench.24Center for Agriculture, Food, and the Environment at UMass Amherst. Boxwood Leafminer: Landscape: Center for Agriculture, Food, and the Environment (CAFE) at UMass Amherst Later in summer, as the leaves toughen, some products stop working; one product (imidacloprid) still cut larvae by about 80%.25Arboriculture & Urban Forestry (AUF). Application of Systemic Insecticides in Relation to Boxwood Leafminer’s Life History A different product, chlorantraniliprole, applied as a soil drench did not control leafminers.26Arboriculture & Urban Forestry. Chlorantraniliprole: Reduced-risk Insecticide for Controlling Insect Pests of Woody Ornamentals with Low Hazard to Bees Whatever you use, follow the label for timing and for bee safety.
Spraying isn’t the only option. Shearing just before the adults emerge removes many infested leaves. Light infestations are mostly cosmetic and can simply be watched.
Cupped Tips and Chewed Leaves From Psyllids and Box Tree Moth
The psyllid is a small sap-feeding insect that makes new leaves at the branch tips curl and cup together, starting in early summer.27University of Kentucky College of Agriculture. Identifying Boxwood Psyllid28WascoNursery.com. Boxwood Psyllid: Identify, Treat & Prevent Leaf Cupping The damage is rarely harmful and is mostly cosmetic.29Kentucky Pest News. Cupped Boxwood Leaves from Boxwood Psyllid A chlorantraniliprole soil drench did not control psyllids, and sprays of that product don’t work on sucking insects.30Arboriculture & Urban Forestry. Chlorantraniliprole: Reduced-risk Insecticide for Controlling Insect Pests of Woody Ornamentals with Low Hazard to Bees Shearing off the cupped tips is often enough. They are this season’s new growth, so cutting them removes the insects’ feeding spot along with the damage. Shear after the new growth has hardened, which keeps the shrub’s tidy shape.
Box tree moth is far more serious. It is an invasive insect from Asia, first confirmed in Ontario in 2018 and now spreading.31University of Guelph. Biology and behaviour of the box tree moth (Cydalima perspectalis) (Walker, 1859), an invasive nursery and landscape pest in southern Ontario Its caterpillars grow to about 1.5 inches long, with shiny black heads and green bodies marked with white-ringed black dots and dark stripes.32Journal of Integrated Pest Management. Identification and Management of Cydalima perspectalis (Lepidoptera: Crambidae) in North America They leave skeletonized leaves, webbing and green-black droppings, and heavy feeding can kill the plant.33Digital Scholarship @ Tennessee State University. Box Tree Moth (Cydalima perspectalis) There can be two generations between May and September.34University of Guelph. Biology and behaviour of the box tree moth (Cydalima perspectalis) (Walker, 1859), an invasive nursery and landscape pest in southern Ontario
The two are easy to tell apart. Psyllid leaves are whole but curled, often with a white waxy material inside the cups, while moth leaves are eaten or reduced to a thin skin. Webbing and droppings point to the moth.
If you find box tree moth, hand-pick the caterpillars and cocoons tucked into the leaves and drop them in soapy water. Check the inside of the shrub, where caterpillars hide in webbing. Bag infested clippings rather than composting them. Report the find to your local extension office or agriculture agency, since many areas track it. Sprays of chlorantraniliprole work as well as standard products against leaf-chewing caterpillars, with low hazard to bees.35Arboriculture & Urban Forestry. Chlorantraniliprole: Reduced-risk Insecticide for Controlling Insect Pests of Woody Ornamentals with Low Hazard to Bees
Yellow Branches From Volutella and Other Fungi
Volutella blight causes cankers, dead areas on stems, that make the leaves on those stems turn yellow to yellowish-brown.36BYGL. Be Alert to Boxwood Blight The dead leaves stay attached for a long time.37BYGL. Be Alert to Boxwood Blight Symptoms often appear in early spring and are commonly mistaken for winter injury.38BYGL. Be Alert to Boxwood Blight The fungus enters mainly through wounds, while unwounded tissue stays healthy.39European Journal of Plant Pathology. Pseudonectria buxi causing leaf and stem blight on Buxus in Canada Shearing cuts, winter breakage and other damage open the door to it.
Winter injury tends to brown whole sections evenly after a hard cold or dry spell. Volutella kills individual stems, so the dead patches are scattered among healthy ones. Peeling back the bark on an affected stem may show discolored tissue, whereas a stem with only winter-burned leaves often stays green underneath. Look for a dead stem with leaves still clinging to it, and ask whether the shrub had a wound there from shearing, breakage or heavy snow.
To clean out an infected shrub, cut the stems back to healthy wood in dry weather. Shake and rake out dead leaves trapped inside, and thin the interior so air and light reach the center. Bag the debris instead of leaving it under the plant. Pruning in dry weather lets wounds dry and close quickly, and thinning cuts let in more air than a tight shear.
Many tiny black dots on the leaves point to a different, non-threatening fungus that mainly attacks shrubs already weakened by poor conditions.40New York Botanical Garden. Research Guides: Boxwood: Boxwood Disease It spreads from the inside of the shrub outward in cool, wet weather, carried by water.41New York Botanical Garden. Research Guides: Boxwood: Boxwood Disease Improving care matters more than treating this fungus directly.
Boxwood Blight and How Green Mountain Holds Up
Boxwood blight is an extremely destructive disease, widespread in North America and Europe.42Plant Health Progress. Boxwood Blight Disease: A Diagnostic Guide Catching it early is the most effective way to stop its spread.43Plant Health Progress. Boxwood Blight Disease: A Diagnostic Guide Unlike Volutella, it does not cause cankers that hold dead leaves on the stems.44BYGL. Be Alert to Boxwood Blight
Look for dark leaf spots followed by fast, heavy leaf drop. Dark streaks on green stems are a key sign. A shrub can go bare within weeks, especially in warm, humid weather. Root rot fades the whole shrub from the roots and leaves soft, rotted roots, while blight starts with spots on the leaves and streaks on the stems. Because the symptoms overlap, don’t diagnose from looks alone. Confirm it through a plant diagnostic lab at your local extension office before acting.
Green Mountain is a hybrid of English boxwood and a Korean boxwood.45Missouri Botanical Garden. Buxus ‘Green Mountain’ One study found it among the least susceptible of the varieties tested.46University of Guelph. Biology and management of box blight caused by Cylindrocladium buxicola A broader ranking places it among the more susceptible varieties.47Journal of Environmental Horticulture. Ranking Resistance of Buxus Cultivars to Boxwood Blight — an Integrated Analysis Don’t count on it to resist blight on its own.
Fungicides can give 95% to nearly 100% control, and combining a systemic product with a protective one works better than a systemic alone.48PubMed. Management of Calonectria pseudonaviculata in Boxwood with Fungicides and Less Susceptible Host Species and Varieties Mulch can block blight spores in the soil from splashing up onto the leaves.49PubMed. Preventing Soil Inoculum of Calonectria pseudonaviculata from Splashing onto Healthy Boxwood Foliage by Mulching In one study, blight spread only between plants whose foliage touched, and frequent watering made it worse.50PhytoFrontiersâ„¢. Increasing Container Spacing and Decreasing Irrigation Frequency Reduces the Spread of Boxwood Blight Among Container Boxwood Plants
If blight is confirmed, remove and bag infected plants rather than composting them, and don’t move clippings or tools to other shrubs. Fungicides protect plants but don’t cure them, so leave them to a licensed professional or follow the label closely. Inspect new boxwoods before planting them near existing ones.
Growing Conditions That Prevent Most Problems
Boxwood won’t tolerate constantly wet sites.51University of Maryland Extension. Common Green Mountain Boxwood Problems and How to Fix Them Water deeply at the base of the plant and avoid overhead sprinklers.52PLANT Design Group. Boxwood Pests and Diseases: What Homeowners Need to Know Keep mulch away from the stems.53PLANT Design Group. Boxwood Pests and Diseases: What Homeowners Need to Know Green Mountain grows about 2 to 3 feet in 10 years and can eventually reach 5 to 7 feet.54Missouri Botanical Garden. Buxus ‘Green Mountain’ Plant it far enough from neighbors and walls that the foliage won’t touch as it grows.
Planting well helps. Dig a hole wider than the root ball but no deeper, so the shrub sits on firm soil and doesn’t settle into a low, wet spot. Set the root ball at or slightly above grade, and loosen any circling roots so they spread outward. Water deeply after planting and keep the soil moist but not soggy through the first season.
Pruning tools can carry boxwood blight from one plant to the next.55University of Illinois Extension. Keeping It Clean Clean tools between plants, and between cuts on a diseased plant.56University of Illinois Extension. Keeping It Clean Some household disinfectants containing quaternary ammonium compounds, labeled “quaternary ammonium,” reduced the spread of both blight and Volutella by tools.57PubMed. Comparative Performance of Sanitizers in Managing Plant-to-Plant Transfer and Postharvest Infection of Calonectria pseudonaviculata and Pseudonectria foliicola on Boxwood