Because honeybees are attracted in large numbers during flowering season, that may create a concern for folks who are allergic to bee stings. To complicate the matter a bit, these trees have lots of pollen but because of their size and structure they are imperfectly pollinated by the bees and other pollinating insects. Consequently a good deal of the pollen becomes airborne. This pollen can be allergenic to folks vulnerable to such a problem. Usually the problem exists under and around the tree and does not affect folks living down the street.
Surface Roots Appear Above Soil Level
Linden Trees are often found growing roots above the surface of the soil. That is usually because they are growing in compacted soils. For solutions see the file Dealing With Surface Tree Roots
Leaves Curled, Distorted
Aphids - Linden aphids are yellow and black with translucent wings. They are the size of a pinhead. They cluster on tree leaves and stems, especially tender new growth, and suck plant juices. Their feeding retards or distorts tree development. They exude a sticky substance that may attract ants. Leaves may turn yellow or brown, wilt under bright sunlight, or sometimes curl and pucker.
Trees Defoliated, Brown Egg Masses On Trunk
Gypsy Moth -Gypsy moth caterpillars grow from about 1/16 inch long at hatching to about 2-1/2 inches long by the time they become pupae. Mature larvae are covered with black hairs and have 5 pairs of blue spots, 6 pairs of red spots along the back, and voracious appetites. In July, they encase themselves in brown shells the trunks of trees to pupate. Gypsy moth larvae are often confused with the eastern tent caterpillar and fall webworm, both of which make silken tents in trees. Gypsy moths do not make tents. Seek out the distinctive sawdust-colored egg-masses on trunks, branches, under your roof eaves, and other protected spots. The eggs look like little gold pearls. Uncontrolled, gypsy moth caterpillars can defoliate a tree completely.
Leaves, Shoots Damaged, Sawdust Visible means Borers
Borers - Adult linden borers are yellowish brown or olive colored beetles. About 3/4 inch long, they have three dark spots on each wing cover. They emerge late in summer and feed on leaves and tender shoots before laying eggs in the bark. Linden borer larvae are slender, white, worms about 1 inch long. After they hatch, they tunnel into the wood, pushing sawdust out of the entrance hole as they progress. They make cavities in trunks and branches causing them to break off. These tunnels give disease and decay bacteria access to the tree. Other borers that attack lindens are the flat-headed apple tree borer and the brown wood borer. About the only way to control borers once they have begun to burrow is to dig them out of their tunnels with a flexible wire or stuff their tunnels with a nicotine paste.
Holes In Leaves
Japanese Beetles - Adult Japanese beetles are ½-inch long, with shiny metallic green and copper-brown wing covers. Their larvae (grubs) are grayish-white, with dark brown heads. These ¾-inch plump worms lie in the soil in a distinctive arc-shaped resting posture. They emerge early in July as beetles and proceed to feed on plant and tree foliage, often skeletonizing leaves.
Leaves Mined or Blotched
Basswood Leaf Miner - Both basswood leaf miner beetles and their larvae feed on leaf undersides. The small, reddish-yellow adult beetles eat out leaf tissues from between the veins. The larvae raise large blister-like mines. Linden foliage turns brown, withers and falls off.
Leaf Edges Brown, Then Whole Leaf
Anthracnose - This is the most destructive of several leaf diseases that occasionally attack trees. A fungus causes it. Leaf edges begin to turn brown and eventually the entire leaf browns and drops off. Ends of shoots look as if they were frost bitten. Serious attacks may defoliate entire trees. Prune away heavily infected branches. Make every effort to maintain plant vigor by attentive feeding and watering.
Reddish-Brown Spots on Bark
Canker - Several fungi cause pinhead sized reddish-brown spots on the bark of linden branches and twigs. These break through the bark surface, providing access for other diseases and pests to invade the tree. Prune out all cankered branches and twigs and collect any that have fallen to the ground. Destroy them.
White Coating on Leaves
Powdery Mildew - Lindens are quite susceptible to powdery mildew. A fungus that develops primarily on the tops of linden leaves causes it. These whitish blotches form well into the growing season. While this fungus makes trees look unattractive, it is not truly harmful.
Circular Brown Spots on Leaves
Leaf Blight. - This fungus causes round, brown spots with dark edges to form on linden leaves. They are often so numerous that they cause the entire leaf to turn brown and fall off. Young trees tend to be more vulnerable to this disease than older, established ones. Be sure to gather and destroy the infected leaves that fall on the ground.
Brown Spots Along Veins
Leaf Blotch - This fungus usually attacks only European type lindens. It causes narrow pale brown spots to develop along the leaf veins, especially near the tip. Eventually an obvious narrow, black stripe appears, dividing the healthy from diseased leaf tissue. In severe attacks a tree may become defoliated. Be sure to gather and destroy the infected leaves that fall on the ground.