Picture this: you’ve planted milkweed, lemon balm, or California lilac, and you’re thrilled to see bees and butterflies fluttering through your garden. You feel good about feeding pollinators and love the life these plants attract to your garden.
As you walk past your beds to check your tomatoes, you notice that they are covered in black spots. Upon closer inspection, it becomes apparent that your plants are infested with aphids.
If your instinct is to seek out a chemical pesticide, stop. While this may eliminate your aphid problem, it will also threaten beneficial insects, which pollinate plants and control pests. Instead, apply the principles of Integrated Pest Management, or IPM.
The practice starts with accepting that some pest presence is tolerable. It is only when this threshold is exceeded that control should be considered. Your first defense should always be the most benign method available. This is where common sense prevails, and it should apply both inside the house and in the garden.
Take my basement: Every spring, ants arrive, but instead of spraying the perimeter of my house with 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. I therefore consider any plant that does not have at least a few holes in its leaves as useless for the ecosystem. Tolerate some leaf nibbling and let nature take its course.
Back to your tomatoes: IPM would dictate washing the aphids with a strong stream of water. It usually works. But if they keep coming back after several tries and you think you need to escalate, take small steps.
The next step in this case would be Insecticidal Soap, a non-toxic pesticide that is safe for humans, beneficial insects (when dry), and most plants (read the label to make sure your plant is not one of the few to be sensitive to the product).
Generally, prevention is the best treatment. Inspect the plants – including under their leaves – before bringing them back from the nursery. Reject anything that shows signs of disease or infestation.
Forgo instant gratification and space plants appropriately to account for their mature height. Crowded plants retain moisture and promote mold, mildew and fungal diseases.
Practice good sanitation by regularly removing dead leaves, fruit, and plant debris, which invite insects, rodents, and pathogens if allowed to remain on the ground.
When you see pests like aphids, clean them up. Dab the scale insects with a cotton swab dipped in rubbing alcohol. Handpick tomato hornworms and cabbage worms (unless they’re coated in the white eggs of braconid wasps, which are little parasitic killers that will kill for you).
Traps can be used to capture slugs. Place shallow containers of beer around affected plants or place small wooden planks on the surface of the soil overnight. You’ll likely have a jar full of drowned slugs – or an assembly of live slugs 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 pesticides in extreme heat, windy weather, or when plants are wet, and apply them only in the early morning or evening when pollinators are inactive. It may hurt, but consider removing the flowers from the plant to reduce the risk to beneficial insects foraging for pollen and nectar. In most cases, more flowers will come.
These pesticides are generally considered safe for pollinators when applied correctly:
Insecticidal soap is a non-toxic option that kills aphids, aphids, lace bugs, leafhoppers, scale insects, thrips, scale insects, sawfly larvae, spider mites and whiteflies by suffocation rather than poisoning. It must be sprayed directly on the insects and loses its effectiveness when dry.
Horticultural oil, another smother, is effective against aphids, aphids, leafhoppers, scale insects, mites, scale insects, spider mites, thrips and whiteflies. The product should come into direct contact with insects when wet and become harmless to 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, aphids, beetles, borers, leafhoppers, leaf miners, scale insects, scale insects, tent caterpillars, thrips, webworms, weevils and whiteflies.
Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium used as a pesticide. Several strains are available, each targeting different pests, so read the label to make sure the product you buy is right for your needs. Some strains are toxic to monarch caterpillars, so do not apply them to or near milkweed, which is their only food source.