Box elder is a tough, fast-growing native maple. That same fast growth comes with a short life and soft wood, and the soft wood is behind the problems that actually threaten the tree or your property.1USDA Forest Service. Fire Effects Information System: Acer negundo2UF/IFAS Extension. Common Box Elder Tree Problems and How to Handle Them Most of what alarms owners, from swarming bugs to blistered or stripped leaves, looks worse than it is, while the quieter structural issues deserve more attention. Whether your tree is male or female also shapes which problems you see, especially with insects.
Which Box Elder Problems Are Serious and Which Are Cosmetic
The easiest way to sort problems is by what they damage. Box elder wood is weak and prone to decay, and trunks or limbs can snap in storms.3University of Minnesota Extension. Common Box Elder Tree Problems and How to Handle Them So anything that affects the wood or bark, like cracked limbs or sunken dead patches, is worth acting on. Leaf and insect problems mostly leave the tree healthy, since established trees regrow lost leaves.4Utah State University Extension. Boxelder Leafroller Boxelder bugs cause at most minor deformed seeds and leaves, or some yellowing on the tree.5National Pesticide Information Center. Common Box Elder Tree Problems and How to Handle Them
A quick walk around the tree tells you most of what you need. Look up for hanging, cracked or split limbs, especially after storms. Check the trunk and the bases of branches for soft spots, cavities or fungus, and note any sunken or discolored bark around old pruning cuts. Leaf spots, bumps and bugs can go on the lower-priority list. A full canopy of green leaves doesn’t prove the wood is sound, because decay often works inside the trunk or limb.
Call a certified arborist when a limb over a house, driveway or play area shows cracks, or when the main trunk has a large decay cavity. Work that needs ladders or sits near power lines is also arborist territory. An arborist can judge whether removal is safer than pruning.
Weak Wood and Storm Breakage
Box elder grows fast, and its wood breaks easily in windstorms or under ice and snow.6Missouri Department of Conservation. Box Elder Decay sets in readily and weakens limbs further over time.7University of Minnesota Extension. Common Box Elder Tree Problems and How to Handle Them
Several signs mark a limb as more likely to fail. Cracks or splits where a limb joins the trunk are a warning, because that joint carries the limb’s weight. Dead branches, hollow spots, and mushrooms or shelf-like growths on the wood suggest decay has already softened it. A branch much longer or heavier than its neighbors, or one leaning out over the house, puts extra load on its attachment.
Pruning correctly lowers the risk. Cut just beyond the branch collar, the slightly swollen ring where a branch meets the trunk, rather than flush with the trunk.8SFGate. How to Prune a Box Elder Tree Make an undercut first so the falling branch doesn’t tear bark down the trunk.9SFGate. How to Prune a Box Elder Tree Remove long branches in several sections rather than one heavy cut.10SFGate. How to Prune a Box Elder Tree Smaller, clean cuts heal better and give decay and fungus fewer entry points.
Late winter, while the tree is dormant, is a good time because the structure is easy to see. Remove weak, narrow-angled or crossing branches early. Small yearly cuts beat large occasional ones, and big or high work belongs with a professional.
After a storm breaks a limb, stay clear of anything hanging and of any lines it touches. Once it’s safe, cut torn stubs cleanly back to the branch collar. Don’t paint the wound; the tree walls it off on its own. Then scan the rest of the canopy for cracks the storm opened.
Boxelder Bugs on the Tree and in Your Home
Box elders are either male or female, and only the female tree makes seeds.11Virginia Cooperative Extension. Boxelder Bug The bugs mainly feed on seed-bearing trees, sucking sap from leaves, tender twigs and developing seeds.12Extension. Boxelder Bug They are drawn to male trees early in the season when those carry pollen, then to female trees as seeds mature.13PubMed. Phenology of semiochemical-mediated host foraging by the western boxelder bug, Boisea rubrolineata, an aposematic seed predator14National Pesticide Information Center. Common Box Elder Tree Problems and How to Handle Them
The trouble starts when cold arrives. Adults spend winter in leaf litter and sheltered spots, including buildings.15Annals of the Entomological Society of America. Survivorship Advantage of Conspecific Necrophagy in Overwintering Boxelder Bugs (Heteroptera: Rhopalidae) Outdoors they rest until warm days, but indoors they stay active until they dry out and die.16Annals of the Entomological Society of America. Survivorship Advantage of Conspecific Necrophagy in Overwintering Boxelder Bugs (Heteroptera: Rhopalidae) Bugs wandering around inside in winter aren’t breeding there and will die off on their own. They don’t bite people or damage the structure.
On sunny fall days, adults cluster on south- and west-facing walls, soaking up warmth before looking for shelter. Those walls are the first places to inspect for cracks.
The lasting fix is sealing. Work in late summer or early fall, before the bugs start looking for winter shelter. Caulk gaps around window and door frames and where pipes or wires enter the wall. Check that door sweeps are intact and that window and vent screens have no tears.
For bugs already inside, vacuum them up rather than crushing them, which can stain fabrics, and empty the bag outdoors. Indoor insecticide sprays add little since the bugs die anyway. Notice where they appear, because that points to gaps to seal.
Spraying the tree rarely stops the house problem, since the bugs travel. Removing one tree may not help either if neighbors’ trees remain.
Leaf Bumps, Rolled Leaves and Leaf Loss
Blister-like bumps on the upper leaf surface, with fuzzy white hairs in a dimple underneath, are pouch galls from a tiny mite.17Penn State Extension. Leaf Galls on Maple The mite lives only on box elder and forms the pockets in spring.18MinnesotaSeasons.com. Boxelder pouchgall mite Infestations while leaves are still growing can leave them distorted.19Penn State Extension. Leaf Galls on Maple Galls need no treatment, and sprays after the bumps appear do nothing.
Leafroller caterpillars look far more alarming. Heavy infestations can strip the whole tree by early to midsummer.20Utah State University Extension. Boxelder Leafroller But box elders can grow a second set of leaves, so trees often look nearly normal by late summer.21Utah State University Extension. Boxelder Leafroller Established trees stripped three years in a row have kept living and growing normally.22Utah State University Extension. Boxelder Leafroller Young or stressed trees have fewer reserves to regrow leaves.
On a small tree you can pick off rolled leaves if you like, and raking up fallen infested leaves helps. Water during drought so the tree can regrow its leaves.
Watch whether the second set of leaves appears; a tree that doesn’t leaf out again needs a closer look. Repeated loss on a tree that also shows dieback or cracked bark is a sign to bring in an arborist.
Telling the problems apart is mostly a matter of shape. Galls are raised bumps, not flat spots. Leafroller damage shows rolled, webbed, chewed leaves. Twisted, cupped new growth without chewing suggests herbicide, covered next. Yellowing with red-and-black bugs on the tree points to boxelder bugs.
Twisted Leaves From Lawn Weed Killers
Box elder is among the plants most sensitive to growth-regulator herbicides, the broadleaf weed killers in many lawn products.23Purdue Extension. Diagnosing Herbicide Injury on Garden and Landscape Plants Even a tiny trace of 2,4-D has malformed very young box elder buds.24Forest Science. The Role of 2, 4-D in the Appearance of a Leaf Blight of Some Plains Tree Species Avoid spraying weed-and-feed products under or near the tree, especially on warm or windy days.
Weed-and-feed is spread over the lawn, but box elder roots reach well beyond the trunk and can take up the chemical from soil. Spray can drift on wind, and some formulations give off vapor on hot days. A tree can be affected even if nobody sprayed it directly.
The damage has a recognizable look. New leaves cup, curl, or turn strap-like and twisted. It often appears on the side facing sprayed areas, tends to show up within days or weeks of spraying, and no insects or bumps are present; together these are clues, not proof.
A single exposure usually leaves later leaves normal. Water and avoid further stress rather than fertilizing heavily. Spot-treat or hand-pull weeds near the tree, and ask lawn services to skip its root zone.
Cankers and Decay in Branches
A canker fungus can infect recently wounded or freshly pruned small branches.25University of Minnesota Extension. Eutypella canker A canker is a patch of dead bark that typically sinks slightly and may crack, with the edges often rolling up as the tree tries to wall it off. The fungus grows under the bark and expands outward up to 1 inch per year.26University of Minnesota Extension. Eutypella canker It kills the living layer beneath the bark that carries sugars and makes new wood, and it rots the sapwood.27University of Minnesota Extension. Eutypella canker An infected branch weakens and is more likely to break, adding to storm risk. Ordinary pruning wounds heal over from the edges, while a canker keeps enlarging year after year.
Look for sunken, cracked bark patches that widen slowly. Prune infected small branches well below the canker, in dry weather. A canker on the main trunk needs an arborist’s opinion. Avoid mower and string-trimmer wounds at the base, and remove dead branches that invite decay.
Sprouts, Seedlings and Spread
Cutting or girdling a box elder doesn’t stop it sending up new sprouts, even with added treatments.28Ecological Restoration. Killing it Softly: Girdling as an Efficient Eco-friendly Method to Locally Remove Invasive Acer negundo Expect to clip sprouts repeatedly after removing a tree or limb. Sprouts appear from the stump and from the roots, sometimes several feet from where the tree stood. The roots hold stored energy, and each clipping draws it down.
Seeds from a seed-bearing tree are winged keys that spin and can land well away from the parent. Seedlings sprout readily in lawns, flower beds, gutters and cracks in paving. Neighboring trees can be the source, so seedlings in your yard don’t always mean your own tree is female. Pull seedlings while small, roots included, and mow or clip stump sprouts each time they appear.
Outside North America, box elder has naturalized as a weed in Europe, South America, Australia and New Zealand.29Rivers of Carbon. Box elder guide: Managing Box elder around waterways Along some southern European rivers it is replacing native willow forests.30Biological Invasions. Light interception principally drives the understory response to boxelder invasion in riparian forests If you live where it isn’t native, check local rules.
Should You Keep or Replace Your Box Elder
Box elder gives fast shade on hard sites.31USDA Natural Resources Conservation Service. Boxelder Plant Guide32USDA Forest Service. Fire Effects Information System: Acer negundo It can be used temporarily until slower, longer-lived trees take over.33USDA Natural Resources Conservation Service. Boxelder Plant Guide Its wind-borne pollen can also trigger allergies in some people. An open spot far from the house, driveway and play areas is best, since a breakage matters less there.
Keep a healthy tree that stands away from structures for shade. Replace a decaying one overhanging the house, and plant a long-lived successor nearby before removal. If you’re choosing a tree to plant, a male one avoids seeds and draws fewer boxelder bugs late in the season.