Managing Incurable Leaf Scorch

By Scott Aker
Special to The Washington Post
Thursday, November 6, 2008

Q I have a wild beech tree I dug from my property about four years ago and have been growing as a bonsai. Every spring, the leaves emerge beautifully, but about six weeks later some of them get irregular brown spots. I feed the tree with a diluted fertilizer every two weeks during the growing season. It is kept outside. I try not to over-water it but make sure the soil and roots stay damp.

Are the brown spots due to watering and nutrition, or is it a disease?

A Your beech may have bacterial leaf scorch. The symptoms are usually confined to or more pronounced on a given branch, and the brown spots appear at the margins of the leaf. Bacterial leaf scorch is caused by a bacterium species that is transmitted by insects from tree to tree. The bacteria proliferate in the water-conducting portion of the wood, reducing the efficiency of water transport to the leaves. Scorch symptoms may not appear until stress is encountered. Stress is much more likely to be a factor for a bonsai than a tree growing in the forest, even if you are paying careful attention to watering.

Placing the tree where it gets afternoon shade may help to alleviate the symptoms, but it won't change the fact that the bacteria reside in the tree. Symptoms will appear again. This leaf scorch cannot be cured. Some tree services may recommend injection of the antibiotic streptomycin, which may temporarily alleviate the symptoms. It is not a cure.

On the brighter side, trees may live for 10 or 20 years with bacterial leaf scorch, and, in good growing conditions, you may see very few symptoms.

I have some daffodils that need to be dug, separated and replanted. Is it too late?

The flowering of daffodil clumps will diminish if the bulbs are in an area that has become shaded or if they are congested after many years in one location. Digging up bulbs is best done when the foliage fades in June so that you can locate them accurately. If you know their position, you can still lift them now. Use a garden fork, which is less likely to slice the bulbs than a shovel as you get underneath them. You will see that the bulbs have already initiated root growth, so you should replant them immediately to prevent them from drying out.

If you have newly purchased daffodil bulbs, the sooner you plant them, the longer they will have to grow roots and become established. If you can't find the time, however, they may be planted as late as November or early December, on a gamble that winter weather will be mild enough to support the root growth they need to make before spring arrives.

Scott Aker is a horticulturist at the U.S. National Arboretum.

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