Tree doctor Howard Burnett.

Dear Tree Doctor: This spring I planted a seedling from the Wye Oak (Maryland's former national champion white oak). The tree is now about 15-18 inches tall and very hearty. The main "trunk" sprouted well with our wet spring and early summer then, after a quiet spell, one of the branches grew rapidly, almost doubling the size of the tree. This vigorous offshoot branch, which is obviously not the main trunk, has caused the tree to have two competing headers, the most dominant being the late-developing branch, which projects out from the main trunk for 3/4 of an inch or so before going straight up. Should I prune the offshoot branch or let it take over? I don't want the tree to have a crook in the trunk.

Douglas Creswell, Mount Airy, MD

The most vigorous branch will take over the leadership position, and one leader is all that any tree needs or it will be forked and thus weaker. I would lop off the weaker shoot and not worry about any stem crook at that point. The tree's healing process will produce callous tissue to finally cover the wound, and succeeding year's annual rings will hide the irregularity in only a few years. As long as your tree is growing vigorously and is adequately cared for, you will probably not be able to detect the crook in three or four years or so.

Be sure to do the pruning so the wound drains rainwater, trimming enough bark at the bottom of the cut so that no water will be trapped. And do not treat the wound with any kind of sealant, regardless of what stores offer. The best recent research finds trees heal themselves perfectly well, and any sealant only encourages insects and diseases by trapping moisture.

Dear Tree Doctor: What causes black spots to grow on (Norway) maple leaves? How can I fix this?

Scott Costello, East Providence Conservation Commission, MA Maples, and some other species, are subject to a number of leaf diseases. A common one is "tar spot" fungal disease, which usually occurs in mid- to late summer. Since the leaves have done the vast majority of furnishing nourishment to the tree by the time mid-summer rolls around, it's a problem in aesthetics only.

To minimize re-infection rate in the future, rake and dispose of all fallen leaves in autumn, and keep the tree healthy by following standard nursery practices for water, fertilizer, and mulch. If the spots are really objectionable, spraying with Bordeaux mixture will control them, but this should not be necessary.

Dear Tree Doctor: My 10 acres in northern Illinois is part of 200 acres with home sites of 10 or 12 acres. It is connected to a corridor of timber via a small river valley. Three years ago the mature red oaks, well away from any building sites, began to die rapidly. One group, a cluster of five, turned milky green, then brown, then dropped their leaves in a two-week period. I suspect they were root grafted. Since then we are losing two or three a year and occasionally a white oak. Is there any practical solution to stop the spread? Will this year's drought help or hurt the situation?

Ken Burtch, via e-mail

Although research scientists are working on this problem, I am not aware of any way to cure or stop the spread of oak wilt, which is spread by root grafts and insects. Root graft barriers might be possible for some specimen lawn trees, but stopping the insects would still be a problem, especially in a forest setting. Again, for specimen trees, pruning only in the dormant season is recommended so as not to spread the fungus by carrying spores on the pruning tools, but this, too, is not for forest settings.

Drought may slow things down but won't stop the spread or effectiveness of the fungus. It would please me to say, "Now for the good news," but I can't. The good news we all want to hear about oak wilt is still ahead of us.

Dear Tree Doctor: While visiting a state park in northern Michigan, I saw a flyer about insects attacking beech trees in the area. Are they similiar to the emerald ash borer or is this something else and is it expected to spread throughout the Midwest?

Betsy Elsaesser, Chicago IL

The leaflet probably refers to beech scale. There are some borers, like the birch borer, and some leaf-eating caterpillars that attack beech trees, but they are seldom serious threats and are best controlled by keeping the trees healthy in the first place.

Beech scale insects are another matter. They are less than a millimeter in size and look like a white powder on the bark of the beech tree. These tiny fellows are suckers and weaken the trees to a point where normally ineffective diseases or insects can cause the tree to die. Beech scale is a major threat to beech across the northeastern United States and Canada, affecting both forest and yard trees.

Ornamentals can be sprayed, but forest tree spraying is out of the question. The only tool forest managers have is to minimize infestations by salvage cuttings to reduce the possibility of spreading. And, of course, cutting of any kind raises objections of one kind or another, and may or may not be possible. As to the expected spread, unfortunately, at this time there is no reason to think beech scale will not spread to wherever there are beech trees.

Dear Tree Doctor: I have three pecan trees; two did not have pecans on them at all this year and last year they were almost all bad. The other one has pecans, but they are all bad. What can I do?

Ferrill Willman, via e-mail

Soil problems are often a problem for pecans. Contact your area Cooperative Extension agent for local recommendations for pecan culture. The agent would also know of any diseases or other problems common in your area.