Call on the good guys to control garden pests

By Kathy Hatfield
Gardening Columnist

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Unless you have a pet chicken instructed to nab only the harmful insects in your garden, controlling insect pests can be difficult. For those who don't like chemical sprays, however, there are alternatives to training poultry.

Among the nuisance insects in Colorado gardens, the following are probably most familiar.

Aphids - These tiny insects feed on the sap of plants, weakening them and causing them to wilt, yellow or have deformed leaves. Often there is a sticky residue on the surface of the leaves. The best control is to spray with a strong jet of water, use insecticidal soap and encourage ladybugs.

Colorado potato beetles - Though its name implies that Colorado is unique as a home for this beetle, the Colorado potato beetle is actually widespread throughout much of North America. Its habit of chewing on tomato, eggplant and potato plants can cause a decrease in fruit production. Aside from hand picking the adults, planting early-maturing varieties can help lessen the damage. Ground beetles, stink bugs and tachinid flies prey on different stages of the Colorado potato beetle. A strain of Bacillus thuringensis, is also helpful in controlling the larvae.

Flea beetles - Just about the time you're craving a spring salad with fresh garden greens, you find that your lettuce is riddled with holes. Most likely, it's the work of flea beetles. These tiny black insects are difficult to spot and are best controlled by using repellent-type sprays, rather than insecticides. Garlic and hot pepper sprays, wood ashes, diatomaceous earth sprinkled on plants, or row covers may help repel the insects or prevent their access to your precious salad greens.

Grasshoppers - Of the uninvited insect guests in our gardens, one of the most destructive and difficult to control is the grasshopper. Though they generally prefer foliage and fruit, like lettuce, corn, flowers and even raspberries, they have been known to girdle woody plants when there are serious outbreaks of these ravenous insects. Grasshopper populations tend to be cyclic, but a serious outbreak can last several seasons. When the spring is cool and wet, there tend to be fewer grasshoppers. A biological control called Nosema locustae, sold as NoLo Bait (and other brand names), is effective if applied in areas where grasshoppers are breeding. Grasshoppers are a favorite treat of turkeys and guinea hens.

Tomato hornworms - The caterpillars of this family become the sphinx, hawk and hummingbird moths that are often seen flying about in the summer months. The voracious and well-camouflaged larvae lurk within the foliage of tomato plants, quickly defoliating them. Fortunately, they can be easily controlled with Bacillus thuringensis, or Bt, an effective biological control specifically lethal to caterpillars but safe to use around children and pets.

One of the best methods of controlling insect pests is having a healthy garden. Just as we are more susceptible to illness during stressful times, plants are more likely to suffer from insect infestation when they are stressed.

A healthy garden starts with healthy soil. Using chemical fertilizers and weed killers kills beneficial insects along with the harmful ones and also disrupts the delicate balance of beneficial microorganisms in the soil. These microbes are necessary to help make the nutrients in the soil available to plants. Organic fertilizers, compost and green manures also contribute to building healthy soil.

Maintaining a healthy garden will also encourage beneficial insects, those that act as pollinators and those that feed on undesirable insects. While it is possible to buy beneficial insects, they generally don't stay put once released, so it's a good idea to provide a garden environment that attracts the "good bugs."

One very helpful insect is the lady beetle, commonly known as the ladybug. Of the numerous kinds of lady beetles in Colorado, all but the Mexican bean beetle are beneficial. Adult ladybugs are known for their appetite for aphids. But like ravenous teenagers, the larval stage can eat as many as 250 aphids per day, 10 times what the adults might eat! Other common beneficial insects include lacewings, praying mantids, parasitic wasps and the spined soldier bug.

Additional methods of control include soap sprays, companion planting, and using herbal teas, such as wormwood. An excellent resource, loaded with information on controlling insect pests, is Whitney Cranshaw's book, "Pests of the West." A web site with links to specific information is http://www.Ext.colostate.edu/PUBS/INSECT/pubins.html.