At some point in your gardening journey, you're going to encounter holes, spots, or blemishes on your leaves, or an unexpected annihilation of your plants overnight. Pests are an inevitable part of gardening, and it's amazing what these tiny creatures can do in a short period of time.
While it might seem like you're waging a war against all these big, bad bugs, the fact of the matter is, only 10% of the insects found in your garden are actually harmful. The other 90% are considered benign or beneficial — that is, they function as decomposers, pollinators, or sustenance for other creatures in the food chain, even if they have destructive habits, like chowing down on your plants.
Fortunately, you can control an infestation if you catch it early enough, and manage a healthy garden without the use of pesticides.
These soft-bodied insects are 1/8-inch long and may be gray, black, green, yellow, brown, or red.
Type of Damage
Aphids feed in colonies and suck the sap out of plants, targeting the undersides of leaves or tender new growth such as shoots and buds. Established plants can usually tolerate a small amount of damage, but young foliage is most susceptible to stunting, curling, or discoloration.
Aphids leave behind a sticky substance called honeydew, which can draw ants to your garden as well. If you suddenly see ants invading your plants, this could be a sign that aphids are nearby.
Aphids usually appear at the end of a season, or when plants are stressed from disease or drought. Proper plant management and watering practices can help reduce the chances of aphids in your garden.
Using a garden hose nozzle with a jet spray, blast the aphids with a sharp, strong stream of water until they fall off the leaves. Repeat every day as needed. For serious infestations, remove the most heavily infected leaves and treat the remaining ones.
Try to avoid over-fertilizing your plants, as excess nitrogen leads to tender new growth, making them especially attractive to aphids.
Slugs and Snails
Slugs and snails are members of the mollusk family, and with the exception of the lack of shells on slugs, the two are very similar. Their fleshy bodies excrete a slimy coating as a protective measure, and they may be various shades of brown, black, or gray.
Type of Damage
Slug and snail damage can be significant, as these pests are capable of devouring entire seedlings and small plants overnight. The telltale signs of damage are irregular holes in the leaves, especially down the center. Often, they'll leave dried slime trails where they've been feeding.
If you find them during the day, hand-pick and destroy them. They tend to hide in decaying plant matter, so be sure to clear your garden of any debris.
Water your plants in the early morning so the leaves have time to dry out before sundown, thereby discouraging slugs and snails.
You can also bait them with a homemade beer trap. Pour about an inch of beer into a shallow pan and place it near your afflicted plants. Slugs and snails are attracted to the yeast in beer, so at night, they'll stretch to reach in and ultimately drown. Clear the pan and replenish the beer every few days as needed.
Caterpillars are the larvae of several different species of butterflies and moths, including cabbageworms, hornworms, and cutworms.
Type of Damage
Most caterpillars chew round and ragged holes in the leaves, with the exception of cutworms, which "cut" the stems of seedlings from their roots. You can often tell when cutworms are the culprits if you find seedling tops scattered on the soil, detached from their bases.
Hand-pick and remove any caterpillars you find on your plants throughout the day. They like to hide on the undersides of leaves and on the stems, and hand-picking vigilance can effectively eradicate them. Certain caterpillars, such as cutworms, may also be found just below the soil surface. Keep an eye out when you turn over your garden bed at the beginning of the season, and destroy any overwintered larvae you find.
Keep your garden beds free of weeds in early spring, since they serve as a food source for newly emerging caterpillars.
If you have an ongoing problem with caterpillars every season, place floating row covers over your crops as soon as you plant them to deter butterflies and moths from laying eggs. Since they still let light and water in, they can be kept in place for the whole season, or removed right before flowering so as not to interfere with plants that require pollination.
These dark brown insects measure 1/2- to 3/4-inch long, and up close, they can look a little intimidating with their large rear pincers.
Type of Damage
Earwigs typically feed at night on foliage, flowers, and fruits, but will also eat dead and decaying plant matter. They leave ragged holes in the leaves or chew on the edges of many common plants. Earwig damage looks similar to caterpillar damage, so to discern between the two, you have to catch them in action at night.
During the day, earwigs like to nest in cool, dark, damp areas of the garden, underneath rocks, paving stones, leaf piles, and garden debris. To deter them, clear any debris, such as dead leaves, that have gathered around your plants.
You can also trap earwigs by rolling up slightly damp sheets of newspaper and placing them in the rows between your plants. The earwigs will take shelter inside the paper tubes and between the layers, and can be discarded the next day.
Another easy and effective trap is filling a shallow container (like an empty tuna can or baby food jar) with cooking oil and a spoonful of soy sauce. The soy sauce attracts the earwigs and the oil drowns them.
These tiny maggots are the larvae of several different species of flies, though some leaf miners are the larvae of moths. Because they tunnel through leaves, they are difficult to see with the naked eye.
Type of Damage
Leaf miner damage is highly distinctive: the maggots tunnel between leaf layers, "mining" out the material and leaving squiggly, blotchy, discolored trails in their wake. While the damage is unsightly, it's rarely harmful to the host plant in the case of ornamentals. Vegetables, however, are more susceptible to leaf miner attacks.
Once leaf miners infest your plants, there's not much you can do. Even sprays and other commercial pesticides are rarely effective, as they need to penetrate the leaf surface to where the miners are, and in the process can kill beneficial insects as well. As soon as you spot leaf miner damage, the best solution is to remove and discard any affected leaves.
You can also cover susceptible plants with floating row covers in early spring, removing them only for plants that require pollination once they flower.
Expert Tip: Bring in the good bugs to help fight the bad bugs. Not all bugs are the bad guys. Many insects, such as assassin bugs, parasitic wasps, lacewings, ladybugs, hover flies, ground beetles, and spiders, are considered beneficial because they prey on destructive pests. Attract them to your garden by growing beneficial plants among your ornamentals and edibles: tansy, yarrow, goldenrod, alyssum, marigolds, cosmos, coreopsis, Queen Anne's lace, wild mustard, and thyme, to name a few.