Sweetgum is a hardy shade tree that pests rarely bother, and it tolerates wet soil better than many of its neighbors.1Woodlawn Conservancy. LIQUIDAMBAR STYRACIFLUA ‘ROTUNDILOBA’ – SWEETGUM, AMERICAN ‘ROTUNDILOBA’ The problem homeowners see most isn’t an insect or a germ at all. It’s yellow leaves tied to the soil the tree grows in.2Woodlawn Conservancy. LIQUIDAMBAR STYRACIFLUA ‘ROTUNDILOBA’ – SWEETGUM, AMERICAN ‘ROTUNDILOBA’ Many of the other troubles that show up on sweetgum, from scorched edges to oozing bark, take hold mainly when the tree is already under stress.
Yellow Leaves From Alkaline Soil
Sweetgum is one of several trees, along with pin oak and red and silver maple, where yellowing leaves are common.3Journal of Arboriculture. Trunk Injection of Iron for the Treatment of Chlorosis of Shade Trees The leaves are making less chlorophyll, the green pigment trees need to turn sunlight into food.4Journal of Arboriculture. Trunk Injection of Iron for the Treatment of Chlorosis of Shade Trees5Utah State University Libraries. Iron Chlorosis of Trees and Shrubs The tree usually lacks iron or manganese, two nutrients it needs to make chlorophyll.6Journal of Arboriculture. Trunk Injection of Iron for the Treatment of Chlorosis of Shade Trees7Utah State University Libraries. Iron Chlorosis of Trees and Shrubs The soil often contains enough iron, though. High soil pH, meaning alkaline soil, locks it away from the roots.8Journal of Arboriculture. Trunk Injection of Iron for the Treatment of Chlorosis of Shade Trees9Utah State University Libraries. Iron Chlorosis of Trees and Shrubs
Affected leaves turn pale green to yellow while the veins often stay greener, which gives the leaf a netted look. It tends to show on newer leaves and across much of the canopy, not on a single branch. You’ll see it often near driveways, foundations and sidewalks, where concrete and fill raise how alkaline the soil is. When the shortage is severe, leaves can also come in smaller and stunted.
Mild yellowing mostly affects looks.10Utah State University Libraries. Iron Chlorosis of Trees and Shrubs Over time, though, a shortage of iron or manganese can lead to scorched leaves, branch dieback and even death of the tree.11Utah State University Libraries. Iron Chlorosis of Trees and Shrubs Yellowing that worsens each year deserves action rather than waiting, and the best time to act is when it first appears in summer, because a tree that is already scorched or thinning is harder to turn around.
A soil test from your local extension office should come before any treatment. The same yellow leaves can come from overwatering, compacted or waterlogged soil, or root damage, so guessing at a fix can waste a season. The test reports pH, which tells you whether alkalinity is a plausible culprit, and it shows what the soil needs before you buy anything.
If alkalinity is the cause, sulfur or acidifying fertilizers can lower the pH, but slowly, over seasons rather than weeks. Iron or manganese products applied to the soil, or injected into the trunk by an arborist, give faster green-up. Mulching and keeping lime away from the tree help stop the soil from getting more alkaline. Spraying fungicide or insecticide won’t fix a nutrient problem.
Scorched Leaf Edges and Bacterial Leaf Scorch
Drought, flooding, wind, road salt, air pollution and nutrient extremes can all brown leaf edges.12APSnet Features. Bacterial Leaf Scorch of Shade Trees This kind of scorch is fairly even around the edges, hits new and old leaves, and covers wide parts of the canopy. It often shows up soon after a known stress such as a dry spell or a salted winter road.13APSnet Features. Bacterial Leaf Scorch of Shade Trees
Bacterial leaf scorch is a disease caused by the bacterium Xylella fastidiosa, which lives in a tree’s water-carrying tissue.14University of Kentucky College of Agriculture, Food and Environment. Bacterial Leaf Scorch of Shade Trees It is spread by sap-sucking insects such as leafhoppers, treehoppers and spittlebugs that feed on that tissue.15University of Kentucky College of Agriculture, Food and Environment. Bacterial Leaf Scorch of Shade Trees The strains found in sweetgum seem to be specialized to it, and strains that cause disease in grapes, oleander and almond did not infect sweetgum.16PubMed. Leaf Scorch of Purple-Leafed Plum and Sweetgum Dieback: Two New Diseases in Southern California Caused by Xylella fastidiosa Strains with Different Host Ranges Symptoms can take many months to appear after infection.17PubMed. Leaf Scorch of Purple-Leafed Plum and Sweetgum Dieback: Two New Diseases in Southern California Caused by Xylella fastidiosa Strains with Different Host Ranges
On sweetgum, the bacterial scorch shows a brown edge with a reddish-brown band on the inner side of the dead tissue.18University of Kentucky College of Agriculture, Food and Environment. Bacterial Leaf Scorch of Shade Trees The scorch is often irregular, with a yellow or red band between green and brown tissue.19APSnet Features. Bacterial Leaf Scorch of Shade Trees It often starts on one or a few branches and spreads to other parts of the tree over time.20APSnet Features. Bacterial Leaf Scorch of Shade Trees
To tell the two apart, watch whether the same branches scorch again, earlier, next summer; that pattern points toward infection, though only a lab test confirms it. One summer’s scorch proves little. A single season after a hot, dry spell is most often just stress, and a stressed tree that gets water and a milder season often looks normal the next year.
The disease is hard to catch early because symptoms can lag infection by many months, so the tree may have been infected long before you noticed anything. The bacterium blocks the tubes that carry water, so leaves dry out at the edges even when the soil is moist. That’s why watering alone does not clear the scorch. It typically appears in mid to late summer, and the brown leaves stay on the branch rather than dropping quickly.
If you suspect it, only a lab test can confirm it. Collect leaves showing symptoms from several places on the tree, taking those from the border between green and brown tissue. Call your county extension office first to ask how they want samples packaged and where to send them, since labs differ. Deliver the sample soon after picking it, kept cool and not sealed wet in plastic. A negative result from a sample taken at the wrong time or place doesn’t always rule out infection, so a repeat test may be worth it if the pattern continues.
There is no cure. Care aims to slow decline and keep the tree safe: water in dry spells and remove dead branches to extend the tree’s useful life. If decline becomes severe, plan to replace it with a different species.
Leaf Spots
Many spots on sweetgum leaves come from conditions like weather or injury rather than germs.21Pacific Northwest Pest Management Handbooks. Sweet Gum (Liquidambar spp.)-Leaf Spots Others involve various fungi and bacteria, including Cercospora, Septoria, Alternaria and a red leaf spot fungus.22Pacific Northwest Pest Management Handbooks. Sweet Gum (Liquidambar spp.)-Leaf Spots
Spots tend to increase after wet, humid springs, when leaves stay damp. Fungal spots often have defined borders and may show tiny dark dots. They are scattered across the leaf rather than following the edge, unlike scorch. They usually start small and may grow or merge as the season goes on, while a nutrient problem changes color more broadly. Spots from hail, chemical splash or wind injury often appear all at once and don’t keep spreading to new leaves afterward. Check leaves from different parts of the tree, since spots concentrated on shaded inner or lower leaves suggest a moisture-related cause.
Leaf spots on established shade trees mostly affect appearance and rarely kill the tree. Cleanup and good airflow usually matter more than spraying. Rake and dispose of fallen leaves to reduce fungus surviving over winter, water the soil rather than the foliage, and thin dense growth so leaves dry faster. Fungicides are rarely worth it on large trees, and they must go on before symptoms appear.
A tree that is otherwise growing well, with normal new shoots and a full canopy, can usually tolerate spotted leaves with no treatment. Late-season spotting matters even less, because the leaves are about to drop and have already done most of their food-making. Worry more if the spots come with early leaf drop several years in a row, which can wear down a tree’s reserves.
Cankers, Bleeding Bark and Dieback
Sweetgum can develop a bleeding condition in which a heavy, motor-oil-like fluid oozes from bark that doesn’t look wounded.23Arboriculture & Urban Forestry (AUF). A Summary of North American Hardwood Tree Diseases with Bleeding Canker Symptoms The inner bark turns dark reddish brown, and white crystal pockets sometimes form in the dead bark.24Arboriculture & Urban Forestry (AUF). A Summary of North American Hardwood Tree Diseases with Bleeding Canker Symptoms The tree’s upper branches often decline afterward.25Arboriculture & Urban Forestry (AUF). A Summary of North American Hardwood Tree Diseases with Bleeding Canker Symptoms A fungus called Botryosphaeria, which causes cankers (dead patches of bark), was found growing on such bark.26Arboriculture & Urban Forestry (AUF). A Summary of North American Hardwood Tree Diseases with Bleeding Canker Symptoms
Some fungi in the Botryosphaeria family can kill sweetgum shoots and cause dieback on young trees.27Tree Planters’ Notes. Fertilization and Irrigation Effect on Botryosphaeriaceae Canker Development in Intensively Managed Sweetgum (Liquidambar styraciflua) On young transplanted trees, though, the fungus did little harm and looks like a weak pathogen.28USDA Forest Service. Effects of Botryosphaeria Inoculation and Stress During Lifting and Outplanting on Initial Growth of Outplanted Sweetgum Seedlings Cankers showed up mainly on trees already stressed, for example by rough transplanting.29USDA Forest Service. Effects of Botryosphaeria Inoculation and Stress During Lifting and Outplanting on Initial Growth of Outplanted Sweetgum Seedlings These fungi may also speed the natural shedding of lower branches.30Tree Planters’ Notes. Fertilization and Irrigation Effect on Botryosphaeriaceae Canker Development in Intensively Managed Sweetgum (Liquidambar styraciflua) Canker fungi often live in the bark without causing harm and take advantage when the tree’s defenses are low, so fixing the stress, such as watering during drought, matters more than treating the fungus. In yard trees, the usual stresses are drought and heat (especially in the first years after planting), mower and string trimmer wounds at the base, soil compaction or construction near the roots, and planting too deep or in a cramped strip.
Cutting off affected limbs well below the damaged bark may help stop spread.31Natural Content, LLC. 7 Common Sweetgum Tree Problems: Signs of Potential Danger Cut in dry weather, into healthy wood, and clean your tools between cuts.
Call an arborist if the oozing is on the main trunk, not just a branch, or if dieback covers a large share of the crown. Cracks or dead bark over large areas can mean weakened, unsafe limbs.
Insects That Feed on Sweetgum
Large green luna moth caterpillars feed on sweetgum but are not pests and don’t cause significant damage.32Texas A&M Forest Service. Luna Moth Forest tent caterpillar outbreaks can strip leaves, mainly hurting looks.33Home & Garden Information Center. Forest Tent Caterpillar Repeated leaf loss over several years, however, can stress a tree, make drought worse, and occasionally kill it.34Home & Garden Information Center. Forest Tent Caterpillar
Chewed edges, ragged holes or leaves eaten down to the veins point to caterpillars or other chewing insects. Dark pellets of droppings on the ground, driveway or patio beneath the tree suggest that feeding is happening overhead, and the caterpillars themselves are often visible on leaves or branches by day. A healthy tree regrows leaves the same season after defoliation, so a single year of loss rarely calls for action. The concern grows when it happens year after year or combines with drought, since the tree keeps spending stored energy to regrow. Then watering during dry spells helps more than anything else, and a certified arborist can advise on targeted treatment.
Wood borers are a different matter. In China, a newly found beetle called the sweetgum inscriber is killing planted American sweetgums.35Oxford Academic (Journal of Economic Entomology). Expected Timber-Based Economic Impacts of a Wood-Boring Beetle (Acanthotomicus Sp.) That Kills American Sweetgum In South Africa, the polyphagous shot hole borer, a tiny beetle that grows a damaging fungus inside the wood, attacks sweetgum.36Journal of Plant Pathology. Chemical control of the polyphagous shot hole borer beetle (PSHB, Euwallacea fornicatus) and Fusarium euwallaceae in American sweetgum (Liquidambar styraciflua) This borer has also become established in parts of California. Insecticide and fungicide treatments only partly protected sweetgums from it.37Journal of Plant Pathology. Chemical control of the polyphagous shot hole borer beetle (PSHB, Euwallacea fornicatus) and Fusarium euwallaceae in American sweetgum (Liquidambar styraciflua)
Borers leave pinholes, fine sawdust or sugary staining on the bark. Report suspected new borers to your state extension or agriculture department.
Keeping a Sweetgum Healthy
Sweetgum is resistant to Armillaria root rot, a common fungus that kills many trees.38Missouri Department of Conservation. Armillaria Root Rot Where that fungus is present, good care and resistant trees are the best defense.39Missouri Department of Conservation. Armillaria Root Rot And since the common yellowing usually comes from alkaline soil, planting new sweetgums in neutral to acidic soil helps prevent the most common problem.40Woodlawn Conservancy. LIQUIDAMBAR STYRACIFLUA ‘ROTUNDILOBA’ – SWEETGUM, AMERICAN ‘ROTUNDILOBA’41Journal of Arboriculture. Trunk Injection of Iron for the Treatment of Chlorosis of Shade Trees Test the planting site’s soil before buying the tree, so you can choose another species if the soil is strongly alkaline. Pick a site with room for the tree’s mature size, and avoid tight strips between pavement and curbs.
If you want to avoid the spiky fruit, the cultivar ‘Rotundiloba’ is mostly fruitless with good fall color, but it lacks the star-shaped leaf.42Woodlawn Conservancy. LIQUIDAMBAR STYRACIFLUA ‘ROTUNDILOBA’ – SWEETGUM, AMERICAN ‘ROTUNDILOBA’
Young trees need the most care. A new tree has lost much of its root system in transplanting and can’t reach as much water as an established one. Water deeply during dry spells, especially in the first three years; slow watering encourages roots to grow downward and outward rather than staying near the surface. Plant at the correct depth, with the root flare visible at the soil line, which prevents a common problem that leaves trees stressed for years. Spread mulch 2 to 4 inches deep in a wide ring, kept off the trunk, and avoid piling soil or mulch against the bark.
Keep mowers and trimmers away from the trunk, and avoid trenching or paving within the root zone. Prune dead limbs in dry weather, and check the tree each summer for spreading scorch or oozing.
Replacement makes more sense than treatment in a few cases: confirmed bacterial scorch in advanced decline, large dead sections over a house or walkway, or repeated severe yellowing where the soil can’t be changed.