Different ways to deal with plant pests

TWO OF MY GARdening friends — both of whom are fond of growing fruit plants — are at opposite ends of the spectrum when it comes to dealing with plant pests.

The first friend keeps a keen eye on his own plants, so when he recently visited my garden, he quickly alerted me to a few apple leaves curling inwards because of aphids, a sponge moth sauntering down the trunk of a plum tree, and the frothy evidence of a spittle bug on a strawberry plant. To this friend, insect trespass is intolerable, and he diligently sprays his plants with the goal of making every leaf, stem and fruit perfect.

My other friend takes a laissez-faire attitude towards plant pests. He gives his plants the minimum amount of care, perhaps a bucketful of water sloshed onto the soil, perhaps an occasional handful of fertilizer. Then again, this friend does not expect his plants to produce what most of us would consider an acceptable harvest.

There are problems with both friends’ gardens. The first friend’s garden gets doused with too much pesticide. This is unhealthy for both him and the environment, and sets the stage for outbreaks of chemical-resistant pest species. In this garden, there is little opportunity for plants to mobilize their natural defenses against plant pests, or for “good bugs” to help out.

On the other hand, in the second friend’s garden, too many of the plants look sick. There, the edible harvest is low in quality and minimal or nonexistent in quantity.

I suggest steering a middle course in one’s attitude towards pests. I try to tolerate a bit of pest damage on my plants. After all, the plants themselves tolerate some amount pest damage with no ill effect at all. Experiments show that when apple trees lose part or some of their leaves, the remaining leaves or portions of leaves compen- sate for the loss with increased efficiency.

Sometimes, pest problems disappear by themselves. Eggplants are predictably riddled with flea beetle holes in my garden and most other gardens in spring; the problem sometimes abates as summer comes rolling in. Similarly, aphid populations often soar, then crash with equal speed. There is, of course, a point where pest damage becomes intolerable to the plant. Then, something must be done. But even when caterpillars threaten to gobble up a whole plant, there may be alternatives to getting out the measuring spoons and mixing up a toxic spray. Many pests can be controlled by trapping (sticky red spheres hanging in my apple trees are going to lure and trap apple maggots), by mechanical means (cardboard collars around trans- plants keep out cutworms), by genetics (butternut squashes are less susceptible to squash vine borers than are buttercup squashes), and by timing (carrots planted in late spring emerge after carrot flies have laid their eggs).

When all else fails and sprays are needed, the ideal pesticide is one which can be directed only against the pest causing the problem. I spray with one of many formulations of the bacteria Bacillus thurengiensis. This spray is actually a disease of cabbage worms that is toxic to cabbage worms and nontoxic to just about everything else, even me.

When all else fails and sprays are needed, the ideal pesticide is one which can be directed only against the pest causing the problem. When cabbage worms start to eat more cabbage leaves than I deem is healthy for these plants, I spray with Dipel (one of many formulations of the bacteria Bacillus thurengiensis). This spray is actually a disease of cabbage worms that is toxic to cabbage worms and nontoxic to just about everything else, even me.

For those aphids on my apple tree, I mixed up some insecticidal soap in a hand sprayer. Insecticidal soap is toxic to many insects, good and bad, so I spot sprayed only the few infested branch tips.

Spraying always should be forestalled as a last resort. This gives potential predators and parasites of the pest a chance to rally; never discount the importance of “good bugs.” Also, there’s no need to strive for one hundred percent pest-free plants in a backyard garden. Just as it takes a lot more effort to go from a grade of “B” to an “A” than from a “C” to a “B” in school, likewise it takes a lot more spraying to go from almost pest free to the one hundred percent pest-free demanded of commercial growers. Is it worth it?

Cultivating a healthy degree of tolerance for plant pests demands close observation of plants on the part of the gardener. This practice should be applied as diligently as, for example, fertilizer. As the saying goes: the best fertilizer is the gardener’s shadow.

Any gardening questions? Email them to me at garden@ leereich.com and I’ll try answering them directly or in this column. Come visit my garden at leereich.com/blog.