How gardeners can control pests and also protect pollinators
Picture this: You’ve planted some milkweed, bee balm or California lilac, and you’re delighted to see bees and butterflies fluttering about your garden. You feel good about nourishing pollinators and love the life those plants attract to your yard.
As you stroll past your beds to check on your tomatoes, you notice they’re covered in black dots. Upon closer inspection, it becomes apparent your plants are infested with aphids.
If your instinct is to reach for a chemical pesticide — stop. Although it might eliminate your aphid problem, it will also threaten beneficial insects, which pollinate plants and keep pests under control. Instead, apply the principles of integrated pest management, or IPM.
The practice of IPM starts with accepting that a certain pest presence is tolerable. Only when that threshold is exceeded should a control be considered. Your first defense should always be the most benign method available. This is where common sense prevails, and it should apply inside the home as well as in the garden.
Take my basement: Every spring, the ants come marching in, but instead of spraying the perimeter of my house with a pesticide, I place ant traps wherever I see activity. After a few days, the colony collapses, and the problem is solved.
All butterflies start out as caterpillars, and all caterpillars chew on plants. So I consider any plant that doesn’t have at least some holes in its leaves useless to the ecosystem. Tolerate some leaf munching and let nature run its course.
Back to your tomatoes: IPM would dictate washing aphids off with a strong stream of hose water. It usually works. But if they continue to return after several attempts, and you believe you need to escalate, take baby steps.
In this case, the next step would be insecticidal soap, a nontoxic pesticide that’s safe for people, beneficial insects (when dry) and most plants (read the label to ensure your plant isn’t one of the few that are sensitive to the product).
As a rule, prevention is the best treatment. Inspect plants — including under their leaves — before bringing them home from the nursery. Reject any that show signs of disease or infestation.
Forego instant gratification and space plants appropriately to allow for their mature sizes. Crowded plants retain moisture and foster mold, mildew and fungal diseases.
Practice good sanitation by regularly clearing away the plant’s fallen leaves, fruit and debris, which invite insects, rodents and pathogens if allowed to remain on the ground.
When you do see pests like aphids, wash them away. Dab scale insects with a cotton swab dipped in rubbing alcohol. Pick off tomato hornworms and cabbage worms by hand (unless they’re covered with the white eggs of braconid wasps, which are little parasite hitmen that will do the killing for you).
Traps can be used to capture slugs. Set shallow containers of beer around affected plants or place small wooden boards on the soil surface overnight. You’ll likely have a jar full of drowned slugs — or a congregation of live ones under the boards — to dispose of in the morning.
If you decide a pesticide is necessary, select it carefully and follow the directions and precautions on the label. Avoid using any pesticides in extreme heat, on windy days or when plants are damp, and apply them only early in the morning or at night, when pollinators are inactive. It might hurt, but consider removing flowers from the plant to lessen the risk to beneficial insects foraging for pollen and nectar. In most cases, more blooms will come.
These pesticides are generally considered safe for pollinators when applied correctly:
Insecticidal soap is a nontoxic option that kills aphids, adelgids, lace bugs, leafhoppers, mealybugs, thrips, scale, sawfly larvae, spider mites and whiteflies by suffocation rather than poisoning. It must be sprayed directly on the insects and loses its effectiveness once it dries.
Horticultural oil, another suffocator, is effective against adelgids, aphids, leafhoppers, mealybugs, mites, scale, spider mites, thrips and whiteflies. The product must come into direct contact with insects while it’s wet and becomes safe for beneficial insects (and ineffective against pests) once it dries.
Neem oil, a pesticide derived from the seeds of the neem tree, is effective against aphids, adelgids, beetles, borers, leafhoppers, leafminers, mealybugs, scale, tent caterpillars, thrips, webworms, weevils and whiteflies.
Bacillus thuringiensis (Bt) is a naturally occurring soil bacteria used as a pesticide. Several strains are available, each targeting different pests, so read the label to ensure the product you buy is appropriate for your needs. Some strains are toxic to monarch butterfly caterpillars, so don’t apply them on or near milkweed, which is their only food source.