Help! I have two beautiful crape myrtle trees planted between my two driveways. They offer great shade for our cars, but all summer long they drop a dewy mess all over the cars.

I have checked for pests but have found none. What might be the cause of this and is there a solution short of removing the trees?

– Jo Veater, Citrus Heights

According to UC master gardener Carol Rogala, it sounds like your trees have aphids. The problem you describe is very common on crape myrtles. Aphids are small, soft-bodied insects with long, slender mouth parts they use to pierce stems, leaves and other tender plant parts and suck out plant fluids.

The dewy mess you mention is excretion from the insects, which is often very sticky. Almost every plant has one or more aphid species that occasionally feeds on it. Many aphid species are difficult to distinguish; however, species identification is not necessary to control them in most situations.

Aphids have many generations in a year. Most aphids in California's mild climate reproduce asexually throughout most or all of the year with adult females giving birth to live offspring (often as many as 12 per day) without mating.

Although aphids seldom kill a mature plant, the damage and unsightly honeydew they generate sometimes warrant control. Many aphid species prefer the undersides of leaves, so turn leaves over to check.

Natural enemies can be very important in the control of aphids, especially in gardens not sprayed with broad-spectrum pesticides. The most well known are lady beetles (a.k.a. ladybugs), lacewings and syrphid flies.

High levels of nitrogen fertilizer favor aphid reproduction because fast new growth is especially attractive to aphids.

Another way to reduce aphid populations on sturdy plants is to knock them off with a strong spray of water. Also insecticidal soap, neem oil and narrow-range oil provide temporary control if applied to thoroughly cover infested foliage.

Many other insecticides are available to control aphids in the home garden and landscape. While these materials may kill higher numbers of aphids than soaps and oils, their use should be limited because they also kill the natural enemies that provide long-term control of aphids and other pests.

You can find additional information on the UC Statewide Integrated Pest Management Website online at www.ipm.ucdavis.edu.

A neighbor had two locust trees that had to be removed due to their very invasive root system that invaded my property and that of another neighbor.

The problem is that the roots continue to sprout in my yard. This has been going on for two years after the trees were cut down.

I use a Roundup type of product on the sprouts, but they continue to appear every week in another location and I don't like to use the herbicide to excess.

What can be done to stop this invasive root action?

I live in a shared-interest community and the home-owners associations says that this is a neighbor-to-neighbor problem.

– Eric Herman, Lincoln

The locust roots will continue to sprout as long as they retain stored energy, according to the UC master gardeners. As long as the roots sprout, they can build up more energy – and keep sprouting.

You need to limit the amount of energy these sprouts – through photosynthesis – are returning to the roots. Dig up sprouts, cut foliage as soon as it appears or apply Roundup as per manufacturer's instructions.

You also need to consider that these trees produce a vast number of seeds that retain their viability for many years, and that some of what you believe to be root sprouts are really juvenile trees.

To test this, try digging a few of the sprouts next time. If they have individual root systems (and aren't attached to a large root from the old tree), they're baby trees and not just sprouts from an old root.

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:

• Sacramento: (916) 875-6913; 9 a.m.-noon and 1-4 p.m. weekdays

• Amador: (209) 223-6838; 10 a.m.-noon Monday through Thursday; email ceamador.ucdavis.edu

• Butte: (530) 538-7201; 8 a.m.-noon and 1-5 p.m. weekdays

• El Dorado: (530) 621-5512; 9 a.m.-noon weekdays

• Placer: (530) 889-7388; 9 a.m.-noon on Tuesdays, Wednesday and Thursdays or leave a message and calls will be returned

• Nevada: (530) 273-0919; 9 a.m.-noon Tuesdays through Thursday or leave a message

• Shasta, Tehama, Trinity: (530) 225-4605

• Solano: (707) 784-1322; leave a message and calls will be returned

• Sutter, Yuba: (530) 822-7515; 9 a.m.-noon Mondays and Tuesdays and 1-4 p.m. Thursdays

• Yolo: (530) 666-8737; 9-11 a.m. Tuesdays and Fridays, or leave a message; calls will be returned

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