Q: My liquidambar trees drip a sticky "sap" that is as hard as a rock when it dries. It is death to car paint. It's only happened two years out of the 25 since the trees were planted.

For the last five years, I have had the trees sprayed so they don't produce (seed) balls. Is there anything that can be done about this sticky situation? It's right over the driveway.

– Betty Miller, Sacramento

A: The problem likely isn't sap; it's aphids, says UC Master Gardener Bill Pierce. Because you are dealing with large trees, there are several approaches for eliminating honeydew produced by aphids in your trees.

Ants go up the tree to harvest the sweet sap that aphids suck out of the leaves. To stop the ants, put a 6-inch band of duct tape around the trunk of each tree about 6 inches above the soil level. Coat this band with Tanglefoot, available at nurseries and home improvement stores. The ants can't cross this sticky substance. You will have to redo this process when the product is no longer sticky due to dust, water, etc.

In conjunction with the Tanglefoot barrier, a forceful spray of water or water-soap solution, even on large street trees, when applied with appropriate equipment (such as a power nozzle) will provide sufficient control of aphids.

If all else fails, you can treat the tree with a systemic insecticide such as Bayer's Tree and Shrub Insect Control. This product, more expensive than the other suggestions, is poured at the base of the tree, where it is absorbed by the roots and is then effective for one year.

Because it takes a substantial time for the product to get from the soil to the growing points of trees, application must be made up to two months before problems are expected. Read and follow directions on the bottle carefully for the quantity to use and optimal application time. Always water the tree deeply before applying such products.

Q: I have two trees in my backyard that sucker vigorously, a pomegranate and a Japanese crabapple. In a new garden plan, there are to be low (12-inch) stone walls about three-quarters of the way around each tree with ferns and other shade plants between the tree trunks and the walls.

Is there anything I can do to prevent suckering without killing the trees or should I abandon my garden plan? I clip back continuously, but the sprouts still come.

– Deborah Weber, Sacramento

A: According to UC Master Gardener Bill Pierce, a product on the market called Sucker Stopper will solve your problem. It comes in a ready-to-use container and kills suckers but does not harm the parent tree. Ask for it at nurseries.

GARDEN QUESTIONS?

Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.

Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h&g@sacbee.com. Please put "Garden Detective" in the subject field and include your postal address. To contact your UC Extension directly, call:

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