The first step in pest management is correct identification. Treating for the wrong pest wastes money and can harm beneficial insects.
The most common culprits and how to spot them:
Aphids — tiny (1/16 inch), pear-shaped, clustered on new growth and under leaves. Colors vary: green, black, yellow, gray. Leave sticky residue (honeydew) and may attract ants. Often arrive in spring and on stressed plants.
Cabbage worms — velvety green caterpillars on brassicas (broccoli, kale, cabbage, cauliflower). Look for round holes through leaves and small green frass (droppings). Adult is a white butterfly with black dots.
Squash vine borers — holes at the base of squash stems with frass that looks like wet sawdust. Stems may wilt suddenly. The borer is inside the stem. Adult moth is red and black, wasp-like.
Tomato hornworms — large (3–4 inch) green caterpillars with white diagonal stripes and a horn at the rear. Hard to spot because they match stem color. Look for defoliated branches and large black droppings.
Cucumber beetles — yellow with black stripes or spots, 1/4 inch. Chew holes in leaves and flowers, and transmit bacterial wilt virus. Very damaging in squash family plants.
Slugs and snails — irregular holes in leaves, usually overnight. Silvery mucus trail visible in morning. Active in cool, moist conditions.
The decision point: Not every pest requires treatment. Light aphid damage won't kill a mature plant. Make a control decision when: damage is widespread, a vulnerable growth stage is affected, or population is exploding.
First response: Handpicking works better than most people expect. A jar of soapy water plus 5 minutes of focused hunting removes a surprising number of caterpillars and beetles.