Struggling Tri-Colour Beech Tree

(Question)

About 3 years ago we planted a tri-colour beech tree in the corner of our back yard. The tree was planted in the fall, and it looked like it had weathered a tough summer sitting in a garden center. It is about 12 feet tall, but very spindly. The corner it is in is full sun until late may when our Oak trees come into full leaf, and then the tree is in mostly shade. The soil is somewhat sandy, but we water regularly.

This spring the Beech tree suffered from several bug infestations. It was covered in a white powder which then evolved into moving fluffy white bugs. Lime green flying bugs were all over the tree, and there were webs on most branches (like spider webs). I sprayed the tree with insecticidal soap two weeks in a row, and hosed the tree down several time. Now most of the leaves are brown and have curled up. There is still some white powder on the leaves. Many of the tree buds didn’t even open this spring. I have put fertilizer stakes around the drip line of the tree.

Nothing I seem to do is helping. My beautiful tree is sick and I really want to save it. I am not sure if I should move it to a sunnier location, but i worry that a move will kill it entirely. Any thoughts on how I can get my tree back to health?
Thank you for your help.

(Answer)

Tri color beech, Fagus sylvatica ‘Roseo-Marginata’ is a striking tree that one doesn’t soon forget. It is often used as a specimen tree due to its variegated leaves that may come in many shades of green, pink, and white. If this show wasn’t enough they also put on a brilliant show of copper coloured leaves in the fall.

This tree should be planted in part shade in well-drained, moist, slightly acidic soil. The tree may be planted in full sun, however the foliage will sometimes burn in the hot afternoon sun.

From your description it sounds as if your tree suffered from an attack of Wooly Beech Aphids. These aphids are pale yellow, sap-feeding insects, which are covered by fluffy white fibers, forming dense colonies on young shoots and the underside of leaves where they tend to congregate. Often large numbers of the molting or cast “skins” will be attached to leaf hairs, which gives the leaf a whitish appearance.

Winged aphids, which have a bluish-white appearance when in flight, fly from infested plants in midsummer in search of other beech trees.

The foliage becomes sticky with the honeydew that is excreted by the aphids and this can lead to sooty moulds. In the case of a heavy infestation the foliage at the shoot tips becomes distorted and the leaves may dry up.

Natural enemies such as lacewings, and parasitic wasps may help to control aphids, but may not appear in sufficient numbers until aphids are abundant. You were correct in spraying your tree with insecticidal soap, however repeated treatments of both the upper and lower surface of the leaf are necessary in order to control your infestation. You may wish to contact a certified arborist to apply the soap.

Beech trees are also susceptible to powdery mildew. As the name implies, powdery mildew looks like white or gray blotches on the leaves and stems of the plant or tree. There are actually several types of powdery mildew fungi, but they all look basically the same. You may not notice a problem until the top surfaces of the leaves turn powdery, but powdery mildew can also affect the lower leaf surface.

The weather has been ideal for this fungus, with hot, humid days and cool nights. Although powdery mildew is unattractive, it is rarely fatal. However it does stress the plant and severe or repetitive infections will weaken the plant, thus opening the plant up for infestations by other insects such as aphids. If enough of the leaf surface becomes covered with powdery mildew, photosynthesis is impaired and infected leaves often fall prematurely

There are some fungicides approved for use in Ontario; see your local garden centre for specific products. However, they must be applied at the very first sign of the disease and it sounds like your tree has been infected for quite a while.

To prevent this disease in the future, make sure that your tree is planted in sun, and not crowded, with plenty of air circulation around it. The fungus overwinters in plant debris, not the soil, so a very thorough fall clean up will be important.

Transplanting the tree away from under the shade of the oak tree is a good place to start. Make sure you pick an overcast, cool day for this task and water the tree well over a two-week period. You may wish to consult a certified arborist before you tackle this project as the weather is becoming increasingly too warm for this task. To find a certified professional arborist in your area to help you visit the Ontario branch of the International Society of Arboriculture.

Good Luck