Issue: December 1st, 1997

Concerns with insecticidal soap

I have an aphid problem on my indoor citrus trees. I've been fighting it for a while but can't get rid of them. During the summer, the trees were on my front patio. I used organic insecticide granules as a systemic insecticide but still had the problem. Next, a friend said mix equal parts Ivory soap, vinegar, and lemon juice as an organic spray. I thought things were ok when I brought the plants inside, but noticed after a few weeks that the little critters were back. I tried the granules again, but now they are more plentiful than ever. I would prefer not to use the Ivory soap mixture again as it is too cold to take the trees outside (and the trees are too big for me to do it by myself). Any suggestions you can give me would be greatly appreciated.

I have four cats, one dog, and a guinea pig so anything I use must be safe for pets. Also, do I have to treat all of my other plants? I have cactus, bromiliads, peace lilies, mini orchids, palm trees (small), prayer plants, shamrocks, aloe, spider, donkey's tail, small ficus trees, gloxinia, and wandering jew scattered around the house.

Hope you can help!

The concern with using the soap solution indoors is the damage to furnishings, carpet, and curtains. If these are covered to protect them from the spray, you should have no problem. I recommend a commercial insecticidal soap for insect control because it is made specifically for that purpose and has directions for use. However, if you choose to use the homemade spray, be careful. In the dry indoor air created by the furnace, you may have more leaf burn than you did when the plant was outside. That may be the case with either homemade or commercial material. Both work partly by removing the waxy covering from the outside of the aphids causing them to dry out and die. Plants also have a waxy covering on the leaves; they are also injured, but usually not killed, by soap or vinegar (degreasing) sprays.

Do you need to spray all of your plants? Only if the aphids have spread to them! If they are kept as some distance and not touching the citrus plant, they may not need to be treated. However, any which are close to the citrus may have a low level infestation and spraying may prevent this from becoming a major outbreak. Pay particular attention to the bromeliad, peace lily, orchids, prayer plant, palms, and spider plants as they have clasping leaves or other hiding places where the aphids can hide from the spray. They are only killed if the spray contacts them directly when it is still wet. Aphids will not be killed by walking across the dried spray. These plants can become a reservoir of aphids and other pests to cause problems all winter.

Test spray a portion of each of these plants first to see if the soap will injure the plant. If the plant shows no symptoms after a week, go ahead and spray, being sure to make the solution no stronger than it was in the test spray.

To do a more thorough job of insect control, apply the spray three times, three days apart. This kills the little aphids which may hatch from eggs after the first treatment. The third spray is just to be sure you caught them all. Many aphids are born live and are never outside the mother as eggs, so this triple treatment may not be as essential with aphids as with other insects, but it still helps to get any insects missed by the first spray.

As far as your pets, keep them away from the spray. Soap sprays shouldn't be harmful to them, but it is good practice to keep them from the area when spraying any material. Once the spray has dried, especially these soap sprays, there should be no cause for concern regarding the animals.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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