Make a tea from herbs. Pour 4 cups boiling water over any or all of the following herbs: basil leaves, borage leaves, chervil, comfrey, crushed elderberries, crushed garlic, marigold flowers, pyrethrum flowers, horseradish root, hot peppers (cut into pieces), catmint leaves, petunia leaves, and rue leaves. Let the tea cool before pouring it into a spray bottle and applying to to the affected plants.
This spray is a general organic pesticide that deters many pests and kills aphids.
Plant different plants in your garden to keep pests away from specific plants. Four o'clocks attract Japanese beetles, who eat it and are poisoned by it. African Marigolds and Dahlias repel nematodes.
Garlic repels aphids. Mint repels mice, moles and ants. Chervil deters slugs and aphids. Borage attracts bees and repels cabbage worms and horn worms.
Dill deters aphids, but attracts hornworm, so don't plant it near tomatoes. Plant horseradish in containers and place them in the potato patch to keep away Colorado potato bugs, or make a spray from the root to spray on the potato leaves.
Plant nasturtium throughout your garden to deter aphids, spider mites, whitefly and cucumber beetle.
Yarrow attracts predatory wasps and helpful ladybugs, which eat aphids. Yarrow is very invasive, so plant carefully. Lavender blossoms repel fleas, whitefly and moths. Catnip deters flea beetles, Japanese beetles, aphids, squash bugs, ants and weevils. Rosemary deters carrot flies, cabbage moths and bean beetles.
Lay branches of these herbs in the rows of your garden: rue, mint, lemon balm (also rub on your skin to repel mosquitoes), and wormwood. As you touch or step on the branches, oils are released that deter pests.