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Q&A: HOLES IN MAPLE LEAVES; PRUNING ICE-DAMAGED OAKS
Question: I planted a sugar maple tree three years ago that now has a 3-4 inch trunk diameter. Each summer, this tree looks like it leafed out in a hailstorm. I've searched for insects but never see any. How can I protect this tree from being attacked this spring?
Answer: It's possible that insects are causing holes in the leaves of your maple tree, but I suspect the problem is bacterial or fungal in origin. Many times a hole in a leaf starts as an infection that kills some leaf tissue and then that portion of the leaf dries up and disappears.
One disease that has really been tough on maples, as well as oak and maples in recent years, is anthracnose. This fungus strikes early in the growing season and causes localized leaf spots. Severe cases cause total leaf drop - this happened a couple of years ago on ash trees.
Bacterial leaf spots are irregular to angular in shape while fungal leaf spots are roughly circular. Reproductive structures called fruiting bodies may appear in the center of the fungal leaf spots while the margins of bacterial spots may ooze small droplets of bacteria. Yellowing of the foliage may occur with both types of spots.
It is possible to apply chemicals to trees to prevent infection by anthracnose and other fungal diseases. Chemicals used include Benomyl, Bordeaux, Mancozeb and Thiophanate. My sources at the University of Minnesota tell me that spraying is generally not practical, since it needs to be done very early and repeatedly, and requires spraying the whole tree. Also, most of the damage is cosmetic so treatment is necessary to save the tree.
One other problem of maple leaves that many people complain about is leaf gall. These are small bumps on leaves that are unsightly but don't threaten the health of the tree. Galls are caused by small mites and treatment is not recommended.
Question: The ice storm in January caused a lot of limb and branch damage to my oaks. Is it safe to prune these branches now?
Answer: It's a timely question, because oak trees - particularly red oaks - are susceptible to oak wilt, a fungal disease spread by picnic beetles that deposit spores of the fungus in fresh wounds of oaks. Oak wilt can kill a red oak in a couple of weeks, whereas white oaks (including bur oaks) usually die over a two or three year period.
Because picnic beetles are most active from May 15 to June 15, University of Minnesota horticulturists generally recommend that no pruning be done to oaks between early April and the end of July.
Once it gets established, oak wilt can really devastate a stand of oaks because it spreads readily underground through root grafts - it jumps from one tree to another, in other words, wherever the roots of two oaks touch. Curtailing the underground spread of oak wilt to nearby oaks is nearly impossible and very expensive since it requires hiring a tree service equipped with a 5-foot vibrating plow to dig a barrier around the infected tree. Treating infected oaks with chemicals has not produced consistent results and is probably not worth the time and expense.
Here's the bottom line: If the ice storm damaged your oaks and you want to trim the affected limbs, do your pruning before the end of March or not until the middle of summer.
If the downed branches and limbs peeled off a section of bark up in the tree and you can reach it with a saw, cut the branch back to the point just behind where the bark is peeled. If this type of cut leaves an unsightly stub of limb, consider cutting the limb off next to the trunk, but don't cut too close to the trunk. Make your cut outside of the swelled area where the limb attaches to the trunk - usually about 1-2 inches out from the trunk.
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PUTTING DOWN ROOTS:
A Delightful Blend of
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