Poisoning pests may not be best for your garden

By JEFF GILLMAN


Take a few steps into your garden and look closely. You'll see ecology at work, though not necessarily in a way that may please you: insects, bacteria and fungi eating your plants.

You might be surprised to hear that this is normal. Insects and diseases are supposed to go after your plants. In fact, a little bit of munching is a sign of a healthy garden. The problem is that most people have trouble figuring out how much munching is too much -- and when they should turn to a pesticide for help.

Only you can decide whether to use poison to control garden pests, but there are some rules of thumb that can help you make that decision. Before you reach for the spray bottle, ask yourself these questions:

What's eating your plants?

Never apply a pesticide if you can't identify the disease or insect that is attacking your plants. Many pesticides are designed to do very specific things. If you spray a pesticide without knowing what the problem is, it's likely that you'll be wasting money (pesticides aren't cheap), killing beneficial insects and bacteria that may have been helping to control other problems and needlessly introducing a poison into the environment -- one that could be toxic to you, your children or your pets. If you don't know what the problem is, don't apply a pesticide. It isn't worth the risk.

How much abuse can a plant take?

A few holes or discolored leaves don't mean a plant is on death's door. Most plants can afford to lose about one-third of their leaves without suffering too much. That's because plants don't have sprays to protect them in their natural environments, so they produce more foliage than they need to survive. If your plant hasn't lost many leaves, spraying may not be worth it.

Does the spray control the problem or just the symptoms?

Plants that are over- or under-watered or over- or under-fertilized often look sick and can attract insects and diseases. Spraying these plants can help control the pests, but it won't address the real problem, which is that your plants aren't healthy.

Read up on any plants that are having trouble. Are they getting the right sun exposure? Have your soil tested to make sure it can sustain what you want to grow.

Or go to a garden center and pick up a water-sensing product. They can tell you whether the soil is too wet or too dry for your plants. (As a general rule, soil should be slightly moist, but not wet. Soil that regularly stays wet more than a couple days won't be good for most plants.)

Is the pest still there?

Too many gardeners use pesticides after the pest has already done its damage and is long gone. Applying insecticides to tent caterpillar nests that are empty or to control holes created by hornworms that have left to form pupa is a waste of money and insecticide. If you can't see the insect, then don't apply the insecticide.

Is the problem likely to get worse?

It can be a good idea to use a pesticide not because a particular pest is bad now, but because it is likely to get worse. For example, if you apply an insecticide when tent caterpillars are small, you'll spray a smaller area and use less insecticide than if you waited until they were larger and had done more damage. This is also true with many diseases. Black spot on rose is best treated before it gets bad. If you're going to try to control it, control it early.

Do I have to do anything?

Applying a pesticide is your choice, but you never need to apply one. Pesticides are poisons. If you're uncomfortable with pesticides, then don't use them. It's as simple as that.

If you are going to use pesticides, be sure to follow the directions on the label, which are designed to help keep you safe while making it tough on garden pests.

_____

Jeff Gillman is an associate professor of horticulture at the University of Minnesota. He has written two books: "The Truth About Garden Remedies" and "The Truth About Organic Gardening" (Timber Press, $12.95).