Issue: June 21, 1999

Rain and lawn watering in New Mexico

We have begun to get some rain. Can I stop watering my lawn at least for a week or so?

Whether or not you need to continue to irrigate your lawn depends on how much water the soil in your lawn has absorbed. If the rain falls rapidly and run-off occurs, then there was little water absorbed into the soil. This will be worse if the ground is not level and the water easily runs off.

You should check the depth of moist soil to determine if you need to irrigate. Use a long screw driver, shovel, or other metal probe to test soil for soil moisture. If the soil is moist six or more inches deep, the probe will penetrate the soil easily to the depth of the moist soil. If the soil is moist to a depth of at least four inches, you can dispense with irrigation for that day. If you have an automatic irrigation system that runs regularly and keeps the soil moist, it would be wise to skip one or two irrigations.

From this, don't think that four inches is the ideal depth of irrigation. Grass roots can reach greater depths in properly prepared soil (by rototilling deeply). The greater the depth of roots in the soil, the more efficiently you may irrigate and the less subject the root system is to drying and temperature damage.

Aphids on Spanish broom

I noticed aphids early this spring attacking my Spanish brooms. I bought a spray recommended by a nursery, but this did not work. I ended up just hosing down the aphids when I water my lawn. This seemed to help although it did not completely solve the problem. At least the bushes are flowering although not as abundantly as last year. Any suggestions?

You did well. I am surprised that a spray labeled for control of aphids did not work well because aphids are not especially hard to kill. However, I agree with your use of strong streams of water to just wash the aphids off the stems. You will not get all of them in that manner, but you should reduce the number of aphids to a level that causes little damage. They will try to climb back onto the plants, but you can keep washing them off. When you don't use insecticides, you maintain an environment that allows beneficial insects to increase. There are several "good" bugs that eat aphids. In time they will appear and eat the aphids, keeping the aphid population low enough to limit their damage. This will reduce the need for you to be out washing the aphids off. If you use insecticides, you can kill the aphids, but you will also kill the lady bugs, lace wings, syrphid flies, and other aphid predators.

Pesticides that kill the lady bugs result in the later return of aphids without opposition from the predators. This "resurgence of pests" occurs much more rapidly than the resurgence of the predators, so it becomes necessary for you to continue to intervene with streams of pesticides or water to keep the aphids under control. Whenever possible, use of low impact pest control methods helps to preserve the predators and reduce the need for constant intervention on your part. When there is a need for pesticides, organic or synthetic, be sure to read, understand, and follow the directions on the label.