The Practical Gardener

One of the chapters in the 1952 edition of the USDA Yearbook of Agriculture is titled “Mosquitoes and DDT.” For at least the previous 10 years, DDT had been used in areas heavily infested with mosquitoes. Heavy aerial spraying of the insecticide had been done in Brevard County, Fla., and Hollywood, Calif. DDT sprays had been routinely applied to the interior walls of all homes and buildings in the Mexican village of Temixco from 1945 to 1948. Salt marshes were sprayed with the stuff from boats in Broward County, Fla. DDT emulsion was siphoned into irrigation water that fed farmland in Kern County, Calif.; that same region saw periodic applications of DDT spray, both aerial and by hand, for half a dozen years in the late 1940s. Numerous counties in Texas were repeatedly sprayed with the stuff in the mid- to late 1940s. These are just a few examples.

The result of all this intensive effort was a tremendous increase in mosquitoes’ resistance to the chemical. Initial applications seemed to devastate mosquito populations. But within three years, DDT dosages were being doubled to get increasingly marginal results.

The first studies of DDT resistance began in Florida in 1947. In 1950, researchers launched a study of DDT resistance in mosquitoes in the Tennessee River Valley, where routine treatment of mosquito populations had been going on for at least five years. Again and again through five years of investigation, researchers found that mosquitoes were becoming resistant to ever-stronger dosages of DDT. Nonetheless, in the concluding sentence of this chapter, the author asserts that further confirmation of these results seemed necessary before drawing conclusions. It’s tough to break away from easy solutions.

Not that easy solutions are anything new: Fumigants have been used to kill insects for thousands of years. Homer referred to the use of sulfur for this purpose. And around 200 B.C., Cato wrote that the fumes from a mixture of sulfur and asphalt would kill tree-infesting insects. But most of the time, such “easy solutions” inflict damage far beyond what is intended. There’s no doubt in my mind that Cato’s concoction indiscriminately sent beneficial insects into the great beyond as well as the critters that were damaging his olive trees.

The long-term, far-reaching effects of a decade or so of DDT use weren’t discerned until the damage was out of control. But the amazing thing about the DDT phenomenon is that it didn’t hurt insect populations; if anything, it made them stronger.

Individually, insects are just little beasts; collectively, however, they have a lot going for them. For one thing, the Insecta class is the most diverse group of all land-dwelling creatures. We don’t really know how many insect species there are, but a common guess is about 1.5 million — about 60 percent of all terrestrial species. Besides being incredibly diverse, insects are also wickedly adaptable, able to exploit an astonishing range of habitats.

I’m not sure what was expected when we started dumping enormous amounts of DDT on various insect populations, but I suspect the goal was annihilation. Half a century after the DDT phenomenon of the mid-1940s, however, there are at least as many pest species as ever, scores of major pests have become resistant to insecticides, and pesticides themselves have become major pollutants. Chaos has sprouted from the seeds of the miracle.

In considering the unexpected results of the DDT fiasco, two simple factors loom large: human arrogance (in assuming that we can dominate nature and get away with it) and human foolishness (in ignoring the clear signals that insects are too diverse and adaptable to be subdued by a single-minded chemical attack).

Still, if arrogance and foolishness had been the only forces at work, it might have been a relatively easy matter to identify the vain and stupid people and shout them aside. But greed is another matter; once humans lock onto a windfall, we are generally reluctant to let it go.

In pest control, the windfall was created by DDT, which catalyzed an explosive expansion of the pesticide industry. The unprecedented initial effectiveness of DDT and its siblings, plus their relatively low cost, created enormous demand for pesticides in the ’50s. This, in turn, attracted vast amounts of capital to create the requisite production capacity to satisfy the demand. Industry expansion was so rapid and massive that it simply overwhelmed the process of formal scientific inquiry. As a result, pest control — which should really be an ecological concern — was delivered into the hands of the chemical industry.

Clearly, many of the problems associated with DDT resulted from the lack of pretesting before it was released as a miracle product. Similar analogies can be made about assorted other “miracle products” that weren’t adequately pretested: asbestos (now banned), pressure-treated lumber (to be phased out within two years), and genetic engineering (coming under growing pressure from consumer groups in America and already banned in some countries).

And, speaking of testing, let’s try a little experiment: Beginning with my fifth paragraph, briefly review what you’ve just read, inserting the phrase “genetic engineering” wherever you see the acronym “DDT.” Throw in a little willing suspension of disbelief as you look back on genetic engineering from 50 years hence, and you can see some unnerving similarities. But my purpose here is not to talk about genetic engineering, nor about the easy way to get rid of insects. Rather, my purpose is to talk about the smart way to deal with these pests.

It’s impressive to me the way invading insects are able to find my garden. I’ve never seen a harlequin bug, Colorado potato beetle or cabbage moth caterpillar anywhere else, except at Jardin Fou. How the heck do they get there? The insects that share the bounty of your garden are almost invariably equipped with incredibly precise chemical detectors, which allow them to sense in some manner — whether smell, taste, movement, light or even magnetism — the tiniest molecule, the subtlest indication that your garden is the place to be.

It’s a given, then, that insect pests will zero in on your garden. So what you want to do is make sure that the bugs that prey on those invaders also find your little corner of paradise.

Accordingly, here are four ways you can encourage beneficial insects to visit your garden — and stay there.

Rage against order: Neat and orderly, weedless rows of veggies — the result of fully tilling your garden space each year — are an invitation to pests to dine undisturbed. Beneficial insects are attracted by a diverse plant environment in which perennial flowers and herbs are mixed with veggies (and, ideally, with wild patches of plants allowed to grow naturally nearby). Your garden may look less orderly, but you’ve created a haven where beneficials want to stay.

Wet their whistles: As important as watering your garden is watering your beneficials. Keep shallow pans filled with water in your garden to allow beneficials to drink. Set partly submerged stones in the pan so the helpful critters won’t drown as they drink.

Plant what they love: Beneficials love the rich nectar found in the Umbelliferae family of plants, including fennel, parsley, dill, caraway and loveage. Encourage Queen Anne’s lace, nettles, lamb’s quarters and wild mustard to grow freely.

And finally, the last and best thing you can do is Educate yourself: Read some books on the subject, or spend a couple of hours on the Internet looking up such subjects as “farmscaping,” “beneficial insects” and “companion plants.” Because, in the end, knowledge is your most powerful weapon in the garden.