Out of Control Pests

First and foremost, Happy Fathers Day! Since you dads are relaxing today you may want to wait until tomorrow to read this. The content may way on your mind.

Let’s discuss two common pests on garden plants and their control. The first is already here and eating with a vengeance and the second is sure to arrive shortly. Aphids and spider mites can quickly devastate an otherwise great landscape or vegetable garden.

Aphids have come out with a vicious appetite in the last couple of weeks revealing themselves through damaged leaves on landscape plants and vegetables. Because the rain has slowed down, these pests are no longer being knocked from plant leaves. Tomatoes offer a great example of how to diagnose an aphid problem. A tomato plant may go from having strong, healthy, green leaves to having leaves that curl, possibly from the top down, almost overnight. You may notice yellowing in the leaves as well. When you wonder what could affect your plants so quickly look to the bottom of the leaf. There you will likely see small dots of clear, cream or reddish colored aphids. Sometimes as small as a pinhead, often like grains of sand, they are hiding in plain sight. This example can be used as a starting point for most plants in your yard or garden.

Spider mites reveal themselves most often through little yellow spots on the surface of the leaf. They start to appear in the heat of summer after the rains dissipate. This yellow stippling on the leaves may be very alarming in its quickness to appear and is usually followed by leaf drop. Very fine webbing can sometimes be seen if the population is high. Spider mites often go unseen on the plant but if you shake the plant over white paper, tiny dots will appear, signaling a spider mite presence.

Both of these pests use piercing and sucking mouthparts to remove plant juices and nutrients from the leaf. High levels of feeding will produce a sticky, clear sap on the leaf. This sap and resulting sooty mold can attract ants. Although they are usually harmless to the plant, ants can be an indicator of a pest population. As the infestation progresses you may notice white casts stuck to the leaf. Once you find these pests there are several ways to control them. The first step is to review the population to decide if it is still manageable or if your plant is in real trouble now.

Natural enemies feeding on these pests can help lower a population over a short time period. Aphids create a new generation every 7 – 10 days and spider mites every 10 days. Ladybug, syrphid fly or green lacewing enemies can control a pest population by feeding. Parasitic wasps can also play a role in control by laying eggs inside the aphid that hatch and consuming the body. The spider mites natural enemies include ladybug, lacewing and predatory mites. If these natural enemies are controlling the pest population then don’t spray as a chemical application will kill them as well.

In either case you may be able to control the problem by using a water hose and a spray of pressured water. This will knock the pest off the plant, usually for good, and may be repeated as often as you like. Focus on the underside of leaves in order to contact the hiding pests. If the infestation is severe on one stem then remove that stem and burn it. This may alleviate the population size enough to allow natural enemies to control the rest. Keep your plant watered and in good health. Plants in good health are better able to fend off attacks by pests.

Sometimes populations are out of control before you notice them. In this case a good insect killer or miticide may be necessary. Some active ingredients to look for on the label include carbaryl, malathion, permethrin and acephate. You may have to spray them every 7 to 10 days for a couple of weeks to control the infestation. In this case you should rotate with a spray of horticulture soap or oil (works great on fruit) to prevent any resistance. Make sure to spray the underside of the leaf, the upper side of the leaf, the stems and any spaces on the plant where insects can hide. Both aphids and spider mites have an uncanny way of hiding to avoid control. Always read the label before applying chemicals to ensure proper application and control without harming the host plant. If you notice natural enemies present, move them to another part of the garden so they can help again later.

Helpful Publication: Barrett, Bruce A. Aphids, Scales and Spider Mites on Home Gardens and Landscape Plants. University of Missouri Extension Publication G7274; University of Missouri; March 2004.

The Extension office is located in Kennett, Missouri at 101 South Main Street (the old bank) on the 2^nd floor. Open Monday – Friday or you can call 573-888-4722 if you have a question. University of Missouri Extension programs are open to all.

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Sarah Denkler, Horticulture Educator
University of Missouri Extension
P.O. Box 160, Kennett, MO 63857
573-888-4722 Denklers@missouri.edu