Diseases Of Linden Trees – How To Recognize A Sick Linden Tree
By: Teo Spengler
American linden trees (Tilia americana) are loved by homeowners for their lovely shape, deep foliage, and beautiful fragrance. A deciduous tree, it thrives in U.S. Department of Agriculture plant hardiness zones 3 through 8. Unfortunately, this attractive tree is susceptible to multiple diseases. Some of the linden tree diseases can impact a tree’s appearance or vigor. For a rundown of the diseases of linden trees and other linden tree problems, read on.
Leaf Spot Linden Tree Problems
Leaf spots are common diseases of linden trees. You can recognize these linden tree diseases by circular or splotchy spots on the leaves. They grow larger and merge over time. These leaves fall prematurely.
Leaf spot diseases of linden trees can be caused by many different fungi. These include an anthracnose fungus and the leaf spot fungus Cercospora microsera. Sick linden trees weaken because photosynthesis is interrupted. In order to deal with leaf spot, prune out infected twigs when the trees are dormant. Also, rake up fallen leaves and destroy them.
Verticillium Wilt on Lindens
If you have a sick linden tree, your tree might have verticillium wilt, which is one of the most common linden tree diseases. This is also a fungal disease that starts in the soil. It enters the tree through root wounds.
The fungus enters the tree’s xylem, infects the branches, and spreads to the leaves. The symptoms of a sick linden tree with this disease include leaves dropping prematurely. Unfortunately, treatment of this disease is nearly impossible.
Canker Linden Tree Problems
If you see sunken areas of dead tissue on your linden tree trunk or branches, it may have another of the most common linden tree problems – canker. The dead spots are usually caused by fungi. If your sick linden tree has cankers, prune off the affected branches as soon as you notice the damage. Prune well below the bottom of each canker into healthy tissue.
If cankers appear on a tree’s trunk, it is not possible to eliminate the canker. Give the tree top care in order to prolong its life.
Other Diseases of Linden Trees
Powdery mildew is another common issue with lindens, and easily recognizable by the white powdery substance that covers leaves and even shoots. New growth can be distorted. The best thing to do is to plant the tree where it gets lots of sunlight and the air can circulate. Don’t give the tree a lot of nitrogen either.
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Our 100+ year old english linden tree has about 10% of the branches dying. In our 20 years living here we have never seen this many branches die. It has been lopsided the last two years with good leaf growth on half the tree and stunted leaf growth on the other. The dead branches are equally dispersed throughout the tree. Could it be diseased or dying?
It sounds like either a borer problem or the tree roots on the barren side may be girdled. Either way, the best course of action is to call a certified arborist to diagnose it.
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Diagnose the Disease
Diagnose fungal canker diseases by inspecting your linden tree’s trunk and branches for growing callus tissues on the bark in a bulls-eye shape that appear during the spring and summer. Some fungal canker diseases grow quickly, rendering the tree unable to form the callus tissues, causing “diffuse cankers” that create shallow, discolored depressions in the bark.
Identify powdery mildew by looking for a powdery white or grayish coating on the linden tree’s leaves, usually appearing in late summer or early autumn during periods of high humidity. Powdery mildew is a fungal disease that begins as round white spots on the leaves, growing to cover the entire leaf surface.
Spot sooty mold by looking for a charcoal-black fungal growth coating the leaf surfaces, fruits, twigs and branches of your linden tree. Sooty mold is a fungal disease that occurs from wind-blown spores sticking to the leaves by adhering to honeydew, a sticky liquid secreted by insects like aphids, scales, whiteflies and mealybugs.
Diagnose wood rot, the most common of which in linden trees is oyster mushroom (Pleurotus ostreatus), by looking for white, flaky rot and clusters of shelflike mushrooms that are 2 to 8 inches wide. The mushrooms are smooth on the upper surfaces, with gills on the undersides and stalks. The disease causes the heartwood and sapwood to decay.
- Diagnose fungal canker diseases by inspecting your linden tree’s trunk and branches for growing callus tissues on the bark in a bulls-eye shape that appear during the spring and summer.
- Diagnose wood rot, the most common of which in linden trees is oyster mushroom (Pleurotus ostreatus), by looking for white, flaky rot and clusters of shelflike mushrooms that are 2 to 8 inches wide.
Infestations of defoliating insect pests is common on the linden tree. The spring cankerworm (Paleacrita vernata), forest tent caterpillar (Malacosoma disstria), linden looper (Erannis tiliaria), basswood leaf miner (Baliosus nervosus), white-marked tussock moth (Orgyia leucostigma), fall cankerworm (Alsophila pometaria), and the gypsy moth (Lymantria dispar) all cause foliage damage to the tree, but are not a serious threat. Scale infestations can also occur on the tree's stems, which can cause the foliage to wilt.
The most serious insect pest of the tree is the linden borer (Saperda vestita). The insect bores long tunnels into the base of the tree. A heavy infestation can seriously weaken a young, old or sickly tree. The tree may die if the insects are allowed to flourish.
- The deciduous American linden (Tilia Americana), a popular ornamental shade tree, grows to a height of 60 to 100 feet.
- The tree often suffers insect infestations, but they pose no real danger to a healthy specimen.
The Linden tree comes in several varieties. Those most commonly seen in North America are:-
- Little- Leaf Linden (Tilia cordata). The Little- Leaf Linden is a medium-large tree with a symmetrical canopy with attractive ornamental leaves. Easy- to- care for and with some of the lowest maintenance requirements of all the varieties, the Little- Leaf Linden requires little to no pruning to maintain its handsome form. In summer, expect to see scores of bees enjoying the nectar of its heavy clusters of fragrant yellow flowers. In autumn, the flowers are replaced by attractive clusters of nutlets.
- American Linden (T. americana). With its wide canopy and large stature, the American Linden (sometimes referred to as basswood, white basswood, beetree linden or bee-tree) is most typically seen in large public areas than in private spaces. Its leaves tend to be coarser than those of the Little Leaf Linden, but it makes up for this with its plethora of beautifully perfumed flowers, the nectar from which makes for a truly delectable honey. Unfortunately, the American Linden is one of the most pest-ridden of all the varieties. Unless care is taken, the tree can often be completely defoliated by leaf-munching insects by the end of summer (although take heart- the leaves will return the following spring). Those trees that survive the summer pests will reward their careful owners with a canopy of beautiful, golden yellow leaves come autumn.
- European linden (T. europaea). The European Linden is a striking, medium- large tree with a loose, pyramid shaped canopy. The average tree will top out at around 70 feet. While easy to maintain, the variety can occasionally grow extra trunks that require early pruning.