5 Reasons Not to Spray Pesticides—Even Organic Ones

Pests can devastate a garden, but before you spray, think twice about how your pesticides could harm helpful garden bugs.

by Lisa Munniksma
PHOTO: Rachael Brugger

It might seem counterintuitive, but spraying to eliminate garden pests can do more harm than good. That’s why many organic or chemical-free farmers choose to use integrated pest-management techniques when dealing with their pest problems. Daniel Parson, manager of Emory University’s Oxford Farm in Atlanta, is one such farmer. He likes to think of it as ecological pest management. An organic farmer since 1999, his pest-management strategy has kept his farm’s bad-bug population at a level he can live with, largely without the use of sprays. Consider these five reasons why you should back away from the spray.

1. Spraying Hurts Beneficials

By spraying at the first sign of garden-pest infestation, you might knock out the pests, but you’re also giving predator bugs—good bugs—zero chance at swooping in and saving the day. The unfortunate thing about organic pesticides is that they’re still pesticides. They still impair and eventually kill bugs—many of them affecting all bugs, including the ones we’d like to keep around. Here are a few examples of organic pesticides that can go awry:

  • Pyrethrum, a plant-derived insecticide, paralyzes and can eventually kill all insects it contacts and is toxic to fish and birds.
  • Diatomaceous earth, a powder made from the skeletons of diatoms, a single-celled algae with shells made of silicon dioxide, disables insects’ and arthropods’ exoskeletons.
  • Spinosad, a broad-spectrum pesticide, causes loss of muscle control in insects via ingestion or direct contact.
    Other organic pesticides, such as Bacillus thuringiensis, could be less likely to damage your beneficial-bug population because they affect a smaller range of insects. However, they might also require more frequent application to be effective, as they degrade quickly. Parson warns that it’s important to spray at the right time and according label directions.

2. Biodiversity Is More Effective

A large swath of crop monoculture gives plant pests an open field to devour as they please. A diverse planting and companion planting, on the other hand, break up the plant-pest buffet and attract hungry beneficial bugs, keeping your insect population in a more natural balance.

  • A buckwheat cover crop blooms every 50 days, is easy to replant after removing, and is easy to plow in. In one Organic Farming Research Foundation trial, Colorado potato beetle larvae were reduced by 95 percent in plots where strips of buckwheat were grown.
  • Parson considers wheat, rye, oats and other grain-type cover crops to be natural enemy habitat. Certain species of aphids attack grain crops but not vegetable crops. Time your grain planting so the beneficials move in to take care of the wheat aphids and then stick around when the vegetable aphids arrive.
  • Cornell University Cooperative Extension suggests growing plants in the Apiaceae family—dill, parsley, carrot, coriander, angelica and parsnip—for their flat-topped flower clusters that attract beneficial insects, particularly predatory wasps and flies.

3. Crop Rotation Works

Crop rotation—moving plant families around your growing area season to season—not only reduces insect-pest damage, it promotes soil health and decreases risk of plant disease. It’s an effective pest-management tool because insects emerge from their winter slumber in the soil to find the delicious crop they remember from last year gone. (“Hey, guys, didn’t we leave the kale right here in December?” asks the harlequin bug.) In one crop family’s place is another crop family, not nearly as inviting to these insects.

4. All Bugs Have a Garden Role

You should learn to identify garden bugs and understand how they fit into the environment. Parson encourages you to get out a magnifying glass when you have an aphid infestation—you should also see syrphid fly (aka hoverfly) larvae just about ready to feed on the aphids. While your focus is often on the pest eating your crop, beneficial insects are often standing on the sidelines, ready to pounce.

“The rule of thumb with beneficials is the smaller it is, the better it’s doing for you,” Parson says. He uses the praying mantis as an example. This is a great bug eater, but it eats all bugs, including the beneficial bugs.

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Additionally, some good bugs look like bad bugs—predatory stink bugs, for example, eat pest insects, though they look similar to brown marmorated stink bugs, which eat plants. With good bugs being potentially difficult to spot, you have another reason to rely less on pest sprays and more on beneficial-support methods.

5. Organics Requires a Holistic Approach

If your farm is certified organic or you’re considering it, you have to outline your pest-management strategy in your Organic System Plan. This needs to include a comprehensive plan for dealing with damaging insects. Spraying can be a part of it, but you need to show you have other pest-management tools in place, as well.

“Beneficials will not take care of a severe problem,” Parson says, so spraying can become a last resort, but with a range of ecological pest-management techniques in place, you might not need to.

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