Why Natural Insect Control Works Better

Interplanting flowers with food crops will promote a balanced insect ecology, which in turn will enable natural insect control without the use of toxic pesticides.
June/July 2010
http://www.motherearthnews.com/organic-gardening/natural-insect-control-zmaz10jjzraw.aspx
This beautiful Maine garden produces fabulous food and bountiful blooms. Such interplanting is the key to natural insect control.


PHOTO: LYNN KARLIN

I’ve always been an organic gardener. Early on, I thought natural insect control meant using an “organically approved” insecticide, such as rotenone, to defeat leaf-eating insects — especially my arch-nemesis, the Colorado potato beetle. I dusted my potato patch several times a season in a struggle to keep the beetle’s exploding population in check, barely managing to bring in the crop. But as I learned more about the ecology of insects such as ladybeetles, lacewings, praying mantises, and assassin bugs — what some call “the good guys” — I worried that blasting away with a powder intended to kill might not be doing them any good either.

One spring I vowed to use no rotenone at all in my potato patch, even if it meant losing the crop. I was amazed to find only five potato beetles on my potato plants during the entire season. I took that as luck-of- the-draw seasonal fluctuation — until I bumped into my neighbor across the road, whose garden was less than 70 yards from my own. “My, my,” she wailed, “ain’t these potato bugs just awful. I dust, and I dust, and I dust — and I’m still out here every day, picking ’em off by hand!”

That was my epiphany about the true nature of the teeming insect community around me, and my garden’s relationship to it. From that moment, I have never used a granule of toxin — however reputedly benign — to deal with insect challenges in my garden and orchard. I now find the potato beetle to be one of the easiest insect competitors to deal with.

How to Sustain a Natural Ecosystem

Using natural insect control makes perfect sense to me now. Who wants to eat food that’s been sprayed with toxic chemicals better suited to chemical warfare than gardening? According to the Environmental Protection Agency, American agriculture uses toxic pesticides at a rate of more than a billion pounds annually, and only a small percentage of those chemicals actually make contact with a target insect. The remainder is irrelevant to insect control, but constitutes an assault on the rest of our ecosystem. Pesticides suppress the soil food web (the foundation of soil fertility), pollute groundwater and natural water systems, and destroy vital pollinators and other species.

My fundamental mistake was assuming “organically approved” insecticides made more sense than using any other garden chemicals. While their “non-target” impacts are not quite so drastic they still do more harm than good. Most are broad spectrum in their effect, and can thus wipe out non-target species. To me, the fact that my greatest success with potato beetles came when I ceased doing anything at all to defeat them calls into question the whole strategy of preventing crop damage by killing whole classes of insects. My decision to reject that model — along with the fact that I’m a lazy old gardener who has always had plenty of “the wild” coming in his garden — made possible a natural, spontaneous, unplanned solution to my problem: Flowering weeds provided food and shelter for insects (no longer suppressed by the rotenone) that eat the eggs and larval stage of the potato beetle. The rest, as they say, is history.

Encourage Insects in the Garden

Plants, being immobile, make a deal with their insect buddies: food and shelter in exchange for moving pollen to other plants of their species, initiating production of seeds. Thus, the more flowering plants, the more insects in the ecology — and the more insect species, the more likely any overly successful species is going to be targeted as lunch by predator species. This simple law of population dynamics suggests establishing a balanced insect ecology as the key to preventing crop damage in the garden and orchard. Far from engaging in a “war on insects,” it’s wise to try to maximize the numbers of insect species, ensuring the abundant presence of species that feed on those insects with a taste for our crops.

To that end, we should make habitat plantings of flowering plants — both annual and perennial, with flowers of all sizes and shapes, and in all parts of the season — as “discos” where ally insects can feed, boogie with others of their kind, and mate. The result is greater insect diversity, and a natural balance between herbivorous (leaf-muncher) and predator (bug-muncher) insect species. Our list of recommended Plants to Attract Bees and Beneficial Insects will help you support the “good guys.”

Many beneficial insects feed on pollen and nectar produced by flowers. To support them, use a 1-to-1 ratio of habitat and crop plantings. That may sound like an extravagant use of garden space, but you can weave many garden plants into your insect diversity project. Here’s how:

Instead of planting your herbs and flowers off in their own little fiefdoms, intersperse them among crop beds.

Allow most soil-improving cover crops to flower, providing insects with nectar and pollen. Buckwheat, alfalfa and clovers, cowpeas, and even small grains shed pollen in preparation for seed-making.

Fertility plants such as comfrey and stinging nettle, grown specifically for their contribution to mulches and compost heaps, support insect diversity as well.

Allow green feeds for livestock, such as rape, kale, turnips, and fodder radishes to flower before harvest.

Ground covers such as mountain mints, yarrow, and violets in the orchard can be chosen for the profusion and timing of their flowers. Ferns do not flower, but they do increase habitat diversity.

Weeds — weeds!? They unquestionably played a role in my success. The “archfiend” dandelion, for example, is a dynamic accumulator of minerals from the subsoil, a nutritious green for people and livestock, and a pollen source that supports insect diversity.

Local Skirmishes

The solution to crop damage is not to launch a “war on insects.” But astute readers may ask what I did with those five potato beetles I found. The answer is, “Squish!” To which the logical response is, “But I thought you said that the solution isn’t killing insects.” The practice of squishing (otherwise known as handpicking), however, is a purely local event, and does not have the devastating impact of broad-spectrum insecticides. Leaf-eating insects, like the rest of us, are opportunists — their reproductive prowess can be awesome. Handpicking can keep their populations from surging to damaging levels before their competition has time to catch up.

There are several other acceptable nontoxic “local skirmishes” you can deploy to thwart particular crop crunchers.

Physical barriers can limit insects’ opportunities. Cardboard collars around new transplants (broccoli, for example) keep cutworms from cutting them off at the knees. Row covers of spun-bonded fabric allow rain, air and sunlight to enter, but block insects from vulnerable plants.

Accommodation. Some exceptionally prolific competitors are simply going to be a factor in the garden no matter what we do, so the best tactic is to try to accommodate their presence while bringing in the harvest anyway. I accommodate the presence of Mexican bean beetles by planting bush beans and pole beans. I get numerous pickings of bush beans even as beetles multiply, and I simply accept the eventual demise of the planting. The hungry beetles move on to my pole beans, but for some reason these bean plants are able to shrug off any amount of feeding pressure and still produce abundantly until frost.

Succession planting is a variant of the above strategy. I get many cuttings of yellow crookneck and zucchini before the plants succumb to mounting pressure from squash bugs. Because cucurbits are so fast-growing, I simply make another planting elsewhere in the garden (perhaps protected by a row cover). The persistence of the squash bugs doesn’t interrupt the flow of squash into my skillet.

Dodgeball. You can time the planting of a crop to miss a critical “window of opportunity” of a problem species. The squash vine borer gets its start from a winged female that lays her eggs on the stems at soil line. Planting after the two- to three-week period when the gravid females are active can result in borer-free crops.

Planting resistant varieties deters some problems. For example, corn varieties with tighter husks are likely to have less earworm damage. If you save seeds from individual plants that do better under pressure from insects, you will be rewarded with more resistant varieties.

On the other hand, you can use varieties particularly susceptible to insects as trap crops to draw feeding insects away from favored crops. Texas A&M researchers found that squash sown at least a week before melons will attract up to 90 percent of all squash bugs in the area. Placing boards around squash plants makes it easy to squish any squash bugs, as the insects love to hide out under the boards (read about MOTHER EARTH NEWS’ squash bug squisher technique).

Poultry power. I’ve found that guineas, confined to the winter squash patch with a temporary fence, will provide 100 percent organic, 100 percent effective control of squash bugs. Chickens ranging in the garden in the preseason reduce slugs and snails. Ducks are great for slug patrol in some crops. Almost all domestic fowl with access to an orchard help prevent insect damage. Geese break the life cycle of fruit-damaging insects by cleaning up dropped fruits.

The Most Important Strategy: Relax!

Manufacturers can sell us poisonous sprays only if they convince us to see insects as a big threat. I hope you will instead see a kaleidoscopic diversity of insects in your backyard as the key to sustainable, chemical-free gardening — and a thing of beauty.

Vegetable gardening without pesticides is not a fairy tale, but a practical, effective program. I have used no broad-spectrum pesticides whatsoever in my garden for well over two decades. I still have problems with some insect species in some crops in some seasons. But every season, without exception, I grow more beautiful, residue-free produce than my family can eat and give away.


Quick Tips for Garden Insect Control

Healthy plants are less vulnerable to insect feeding pressure than weak, sickly ones, and maintaining soil fertility helps plants outgrow insect damage. Habitat plantings also benefit pollinator species, crucial in setting seed and fruit in many food crops.

Remember the needs of insects in winter, and don’t go to excess with fall cleanup chores. My comfrey beds look somewhat messy when their leaves die in the fall, but I leave them in place as winter shelter for insects and spiders.

Pass on purchasing beneficial insects. They are expensive, and on release usually go where they want to, not necessarily where we want them to. If our garden ecology is welcoming to ally insects, they will come. If not, purchased beneficials may give marginal results, but they probably won’t thrive.

Remember to encourage other players in the backyard ecology as well. A small garden pool is a magnet for toads, frogs, and lizards, all of which eat a lot of insects. Support insect diversity while providing nesting sites for birds with “edge habitat” in the form of flowering hedges, or use privacy screens made from flowering vines in lieu of manufactured fencing. Respect bat habitats (a hollow tree, an outbuilding) to encourage their insect feeding.

Just two munches by a feeding insect on the tiny leaves of plants emerging from the seed, and it’s all over. However, plants with more developed leaves can shrug off a lot more feeding, so I start as many crops as possible as transplants, rather than direct sowing.


Resources

Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control
(University of California Division of Agriculture and Natural Resources Publication 3386; University of California Press, 1998)
A comprehensive guide to the diverse world of garden insects.

American Beauties Native Plants
Learn about native flowering plants to attract insects.


Harvey Ussery gardens and raises poultry on his homestead in Hume, Va. He is writing a book, The Modern Homestead Poultry Flock, to be published next year.