Yard and Garden: Summer Trees

AMES, Iowa — Iowans are noticing changes in their trees this summer and asking Iowa State University Extension and Outreach horticulture specialists about symptoms that may indicate stress or decline in the health of their trees. The specialists answer several of those questions and are available to answer additional questions through the Iowa State Hortline at hortline@iastate.edu or 515-294-3108. Visit the Yard and Garden FAQs website at http://expert.hort.iastate.edu/ to find answers to tree and other yard and garden questions.

Why is my birch tree dropping leaves?

The loss of leaves is probably due to hot, dry weather or Japanese beetle feeding. 

The hot, dry weather in recent weeks has been stressful to trees. Some trees, like the river birch, cope with the hot, dry weather by shedding some of their leaves. Leaves in the interior of the river birch turn yellow and drop to the ground. Healthy, well-established trees should not be seriously damaged by the hot, dry weather of recent weeks. The hot, dry weather poses a more serious risk to trees in poor health and those planted in the last three to five years. Recently planted trees should be watered approximately every seven to 10 days during dry weather.

Japanese beetles feed on more than 300 different plants. Some of their favorites are linden, elm, birch, pussywillow, cherry and some crabapple varieties. Japanese beetles eat the leaf tissue between the veins, leaving lacy-looking or skeletonized leaves. The skeletonized leaves turn brown. Many of the damaged leaves drop to the ground. Defoliation of well established, healthy trees is usually not fatal. Defoliation is most harmful to recently planted trees (those planted in the last three to five years) and trees in poor health. A thorough watering every seven to 10 days during dry weather should help young trees cope with the loss of their foliage.

My sycamore is losing some of its bark.  Is there something wrong with the tree?

Shedding bark on some trees is a completely normal development. The bark of most young trees is smooth and thin. As the tree grows, the bark layer thickens with the outermost tissue eventually dying. Continued growth pushes the bark outward, sometimes causing the outer layers to crack. On some trees, the outer dead layers peel and drop off, revealing the inner layers of bark. Shedding or peeling bark is characteristic of trees such as sycamore, redbud, silver maple, paperbark maple, shagbark hickory, birch and lacebark pine. The grayish brown bark on a large sycamore tree, for example, flakes off in irregular blotches, revealing a cream or whitish gray inner bark. The loss of the outer layers of bark on sycamores is completely normal.

There is a pile of sawdust-like material at the base of a large tree. What could be the problem?

It’s likely the pile of sawdust-like material was produced by carpenter ants. Carpenter ants commonly nest inside older, hollow trees or in trees with dead limbs or branches. Carpenter ants do not eat wood. However, they excavate some of the soft, decaying wood inside the tree to form their nest cavity. The sawdust-like material is often deposited in a pile at the base of the tree. Carpenter ants do not seriously harm trees. However, extensive wood decay weakens a tree and makes it more susceptible to storm damage.