The Garden as Ecosystem



Twentyfive years ago, Integrated Pest Management (IPM) seemed a utopian dream to mainstream agriculturalists. The idea that plant pests could be kept at acceptable levels without large amounts of chemical pesticides ran counter to everything they had been taught. But now IPM is embraced by nearly everyone involved in the field. What has caused this turn around?

Chemical Miracles

When chemical pesticides were first introduced in large quantities in the 1940s, they were seen as miracles of modern life. Now all farmers had to do was spary their crops with DDT, or some other chemical, and they could achieve complete control.

But within a couple of decades, problems began appearing. The most important of which is the environmental harm done by chemicals which are both toxic and persistent. Even 25 years after being almost totally banned in the U.S., DDT can still be found in the tissue of animals.

But even disregarding environmental concerns, there were a number of other factors that called into question the wisdom of such uninhibited use of chemicals. First, when using an insecticide to control a pest, its natural predators are often killed off as well. This can have the unintended effect of actually causing an upswing in the pest population.

Second, many insects can very quickly develop populations resistant to a given chemical.

And third, when one pest is eliminated the door is opened to others that were less apparent before their competition was killed off. At first the solution to these problems seemed to be to just use more, or different, chemicals, but eventually it became obvious this was no more than a good way to line the pockets of chemical manufacturers.

Avoiding the Problem

The first tenet of IPM is to try to avoid the problem in t he first place. Plants have natural defenses against pests. Problems are more likely to occur when a plant is stressed by its general condition. A plant that receives inadequate moisture or too much sun is less able to put up a resistance to the onslaught of insects.

And those that are planted in too shady a spot, are planted too closely together or get watered in late evening are more likely to suffer from fungi. To minimize problems with fungi, make sure the plants are mulched, have plenty of air circulation and are watered in morning. Try to keep them outside the drip lines of nearby trees and remove the severely damaged twigs and foliage.

Many insects feed primarily on just one genus, or even species, of plant. For instance, the rhododendron lace bug, Stephantis rhododendri, feeds almost exclusively on rhododendron. While its cousin, S. pyrioides, feeds mostly on azaleas. Large, single-species groupings of plants, so popular with landscape designers, are a sure way to create problems.

By the time you notice the Corythucha cydoniae (yet another lace bug) in that huge bank of cotoneaster, it will be too late. Within a few weeks they will have a permanent footing and you will be locked into periodic sprayings of insecticides. By diversifying your plantings you minimize these risks. This doesn't mean you can't have small groupings of particular species or cultivars, just avoid those truly massive displays.

If you want to avoid using chemicals entirely, you may have to do without some plants. Except in ideal conditions, most hybrid roses require regular sprayings. Then again, if you can be satisfied with the less dramatic blooms of the rugosas or other landscape roses you can minimize the use of fungicides and insecticides and perhaps avoid it altogether.

Picking the right plants for the right places, planting them properly and giving them adequate care are key to minimizing the use of pesticides.

Striking a Balance

Integrated Pest Management involves using a variety of methods to control pests. But more importantly, it involves deciding when to use those methods. The point is to only deal with pests when the health of your plants or their aesthetic value is in jeopardy.

The latter is obviously a somewhat subjective call, but we all need to relize that no matter what, we will have pests in our gardens. For instance, in my garden I frequently see dozens of aphids munching on my Irises. But they have no effect on the blooms and they can't even be seen without looking closely.

If I spray them (even with an insecticidal soap), I may harm my very healthy population of praying mantises by eliminating part of their food supply (they love to dine on aphids). These insectivores may be holding in check other pests that I'm not even aware of. So by spraying my Irises for aphids, I may be endangering other plants to other insects.

A lawn is another example of a situation where the best solution is often to do nothing. Assuming one of the reasons you have a lawn is so children can play on it, you might want to avoid using chemical weed killers.

If you've planted the right grass for your area, and take care of it properly, it will generally be strong enough to compete.

Natural Controls

There are a myriad of natural controls at work in your garden. Lady beetles, mantises and spiders are all there eating insects. Parasitic wasps lay their eggs in the larvae of other insects where they hatch and devour them from within. And as mentioned earlier, healthy plants themselves produce a variety of means for controlling pests.

You can purchase lady beetles, parasitic wasps and mantis egg casings for release in your garden, but they are probably there already. If someone has been a little heavy handed with insecticide, it may be worth purchasing some of these predators to replenish their populations. Otherwise, introducing more than your garden can sustain will either cause a massive die out or a migration to greener pastures.

Either way you've wasted your money.

The best way to maintain a healthy population of predators is to avoid using insecticides, and when you do use them, make sure you are only applying them to the areas at risk.