The good and bad news about ants and plants

UC Master GardenerSeptember 8, 2010 

Apply a sticky barrier to prevent many ant related plant problems. uc regents master gardeners 9-8-10

“Help! I have ants in my plants!”

Just as a weed is a plant out of place, insects in the wrong place are pests. Ants play a very important role in the ecology of your garden for good and for not so good.

First, the good news: Ants are predator and prey since they eat the eggs of many insects and serve as food for birds, lizards, and other beneficials. Their tunnels aerate the soil and allow water and nutrients to flow directly to the plant roots. They also distribute seeds by storing them in their tunnels.

The bad news is that ants can protect honeydew-producing, sucking insects that do a great deal of damage. If you manage your ant populations, you will be closer to managing scale, mealybug, aphid, and whitefly populations in the garden.

Diligence is required in monitoring ants, and applying the most appropriate me¬chanical, sanitary, or chemical controls. Exclude ants in the garden by wrapping trunks or stems with a collar of heavy paper, surveyors tape, or fabric tree wrap so that you can apply a very sticky barrier like Tanglefoot to the paper, tape or fabric. Trim the plants so that they do not touch other plants or structures. Leave only a single access point so ants will have to climb the trunk to reach the foliage. To keep ants out of the house, you will have to caulk potential entry points, keep ant food sources (sweets and proteins) closed tightly, and limit their access to water. Keep it clean!

Baits with slow-acting insecticides are the only type of chemical control suggested in most situations. Bait products must be slow acting that foraging ants make it back to the nest. Foraging ants will carry the bait back to the nest and feed it to the developing larvae and queen to kill the colony in a few weeks. Baits combined with sweets or proteins should be placed where the ants can find them easily, but away from children. Baits are in the form of ant stakes, gels, and solids in bait stations. The best results depend on the ant species. Check the University of California IPM web-site (www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7411.html) for species-specific information. You will also find notes on identification and control.

Additional controls are often necessary for aphids, mealybugs, and whiteflies that include: a strong stream of water, hand-removal, an insecticidal soap, neem oil, or narrow-range parifinic oil spray for short-term control. Avoid the use of insecticides that kill natural enemies.

Scale insects can also be reduced with narrow-range oil sprays when the young crawlers are moving on the plants. Aluminum mulch, as a foil-backed paper, will help reduce whiteflies and aphids. Just remember to remove it if the weather gets too hot.

Ants and honey-dew insects make a great team for invading your garden. A coordinated approach is your best bet to control these pests.

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