Insects and Other Plant Pests

When discussing plant pests, we prefer to list natural, or organic, remedies where possible. Garden stores also sell chemical insecticides. When choosing insecticides, choose a soap-or-oil based product, as they will be less harmful and remain on the leaves longer. Mix according to the manufacturer’s recommendations, always wear protective gear and cover exposed skin, and dispose of containers properly. Insecticides are poisons.

Plant pests are found inside on ferns, philodendron, dieffenbachia, and dracaena (dumb cane), as well as flowering house plants like African Violet, bromeliads, orchids, begonias and gloxinia. More rare items like bonsai, alpines, dwarf evergreens, succulents and cacti are not exempt from their predation, either. Inside, these pests are somewhat easier to control, if only because we spot the damage sooner. Outside, in warm, damp climates, pests run rampant, attacking trees, shrubs, ornamentals, annual and perennial flowers, fruit trees and shrubs, garden vegetables, and even weeds.

Categories of plant pests

Plant pests can be divided into about three categories: those that suck plant juices, those that eat leaves, and those that bore into wood. In the first category, aphids – or plant lice – rank number one for their destructive capacity. There are 4,000 species, of which 250 have earned most-wanted posters. Aphids are tiny, greenish white to green, sometimes pinkish or brownish depending on their maturity, and often have lacy wings. They are usually found in colonies, and often with ants, which ‘farm’ them the way we raise cows. To get rid of aphids, blend a hot (habanero) pepper in one cup of water and spray the affected plants.

Spider mites are so tiny they look like reddish or greenish powder on leaves and stems, until you look closely and see the powder moving! Watch for them on tomatoes, peppers and roses. The leaves will look burnt. Try mixing 1 tbsp. buttermilk, one cup unbleached flour and four cups of water and spraying it on the plants. If you smoke, soak a pack of cigarettes in a gallon of water, add a few drops of Ivory liquid, and spray. For scale insects, you can buy fish emulsion fertilizer, mix 2 tbsp. in one quart of water, and spray. The above remedies also work on leafhoppers and whiteflies.

The second category – insects that eat leaves – includes caterpillars, leaf miners, leaf beetles and sawflies. Everyone knows what a caterpillar looks like; what everyone doesn’t know is that not all caterpillars turn into butterflies or moths. Some turn into wasps, and wasps, though ugly, are often beneficial to gardens because wasps eat other bugs. Caterpillars infest plants by rolling up in the leaves. These leaf balls resist spray (the caterpillar inside just laughs!). Picking off damaged leaves and disposing of them is time-consuming, but one of the best ways to get rid of the scourge. Skeleton-like leaves are also a caterpillar sign. Leaves with chewed edges are usually leaf miners. Sawflies masquerade as caterpillars, lay eggs, and ravage roses. Sawfly larva have, in addition to real legs, body bumps that look like undeveloped legs. Sawflies have a natural predator, the paper wasp, but because of overuse of insecticides paper wasps are increasingly rare. Try mixing a strong solution of garlic and Ivory soap in a blender (a lot of garlic, two drops of soap) and spraying them.

A third category of garden pest, the wood borers, terrorize trees and woody shrubs like dogwood and rose, leaving holes or snakelike abrasions up the stalk. Unfortunately, cambium miners or leaf miners can leave the same kind of sign. The cane-boring wasp, which damages roses, also eats aphids and is a garden helper. If your pest is truly a wood borer, or cane borer, you can cut the stalk below the hole, seal the stalk with carpenter’s glue, and burn the cut portion to destroy larva or borer. Normally, wood-or-cane borers will not kill a rose, merely disfigure it. Of greater concern is the raspberry cane borer, which can destroy the entire plant down to the root. Again, cutting the cane, sealing it and disposing of the stalk is the best remedy. If there are too many to tend to individual canes, mix sulfur and lime with several drops of vegetable oil and spray.

Bark beetles, like the notorious Dutch Elm bark beetle, can destroy entire geographic regions of trees. However, it is not the beetle that destroys, but the disease spores it carries. I have had some luck wrapping the trunks of young trees with cloth strips soaked in hard cider, but for mature trees, Dursban – a toxic, organophosphate insecticide – applied to the trunks of the trees fully six feet up in early fall is the only known cure. The pine-bark beetle is another scourge, and equally poorly controlled. I have had some success with pyrethrines (natural organic compounds from the Chrysanthemum family) and verbenone, a natural organic terpene from the verbena family.

It is important to remember that chemical insecticides do not discriminate. They kill both harmful and beneficial insects, as well as people, pets, and plants if overused. Newer organic compounds, like pyrethrines, are safer but still somewhat indiscriminate. Even completely natural substances like vinegar can kill both harmful and beneficial insects. Before you use anything, be certain that it is necessary. Sometimes, waiting a season, moving the plants, or creating better growing conditions (appropriate amounts of water, sufficient room for air and light to penetrate, or aerating the soil) can eliminate unwanted garden visitors as effectively as a toxic spray.