Watch for aphids and spider mites. It’s easy to spray them off with a hard blast of water. Be sure to get the undersides of the leaves.
Ladybugs and green lacewings will be chomping down those aphids, so watch for them and their larvae.
Aphids and other insects can create sooty mold on plants, a fungus that develops from their secretions (honeydew). Wash off the culprits and the leaves. Remove damaged leaves to the trash (not the compost pile).
Watch for tomato hornworms on tomatoes: squish or spray the plants with Bt (Bacillus thuringiensis), a natural caterpillar control that won’t harm you or pets–only caterpillars!
To fend off squash vine borers, keep row cover on and hand pollinate. Or take your chances with natural bee pollinators!
Walk the garden in early morning to pick off stink bugs and largus bugs from tomatoes. Check under the leaves for eggs.
Deploy grasshoppers while young. If you wait, you won’t be able to deal with them. Effective baits include Nolo Bait or Semaspore. Both contain a protozoa called Nosema locustae which is impregnated in bran flakes sweetened with sugar. Apply by hand or with a rotary spreader, early in the morning, when grasshoppers are feeding.