Agri Leader

Enlist plants to control garden pests

To control pesky insects like scale, mealybugs, aphids, whiteflies and thrips, try getting out your shovel and spade. No, you won't be swatting at them like a superhero, instead you will be using these simple garden tools to help plant insect-inhibiting plants. Interspersing the right plants in your garden beds can help keep problematic insects from taking over. "Many herbs are good choices for this purpose-thanks to their oils and scents," said Debbie Hughes, a certified horticulturist and a site historian at the Edison & Ford Winter Estates in Fort Myers. Artemesia, Cuban oregano, scented geraniums, lavender, nasturtiums, pennyroyal, plectranthus, rosemary, salvias (including sage), yarrow, and even Tetradenia, an African moth-repellent plant, are those that Hughes recommends planting. Unwanted garden insects also include those that exist at a microscopic level. For example, nematodes are microscopic roundworms that attack roots and feed on the water and nutrients of host plants, particularly tomatoes. To combat nematodes, marigolds provide a colorful and effective solution if used correctly. "Many people use marigolds to help decrease the nematodes," said Hughes. Research conducted by the University of Florida finds the use of marigolds, allelopathic, meaning they inhibit the growth of other organisms.
Hughes explained that this inhibition is particularly relevant when marigolds are grown as a ground cover for about two months, tilled under, and then the desired plant is planted in the same spot. The end result of using marigolds for nematode control varies. More information can be found at: In addition to providing protection against insects that invade plants, certain plants can be planted for the purpose of keeping other types of pests away. For example, mosquitoes can be repelled with the addition of citronella and rose geraniums. "Rubbing the plant leaves over your skin will assist in repelling certain biting insects," said Hughes who mentioned that garlic chives also work well. Fleas can also be kept under control with the right plants. "Pet owners make collars containing dried pennyroyal to inhibit fleas from dogs and cats, while others line their garden beds with the herb," said Hughes. To keep other types of garden pests away, such as animals that dig in your garden, you can plant cat-away plants, such as Cuban oregano or Plectranthus caninus (mint family). "The fragrance of the Plectranthus caninus gives it another name, 'the stinky plant,'" said Hughes. While some plants keep garden pests away, other types can be used to invite good bugs in. "Herbs in the carrot family, such as dill, fennel, parsley are all host plants for the Eastern Black Swallowtail butterflies," said Hughes, who explained that the female butterflies lay eggs, tiny yellow dots, on the tips of these plants. When the eggs hatch, the caterpillars chew on the leaves until they are ready to go to the next stage and eventually emerge into a butterfly. "Butterflies are major pollinators of many of our ornamental plants," explained Hughes. Bees are also major pollinators. "African blue basil is a good choice for attracting bees," said Hughes who explained that the bees don't bother her while she is gardening as they are busy gathering nectar. "Any plant containing high amounts of nectar attract pollinators such as moths, butterflies and bees," said Hughes. Sunflowers, Coral honeysuckle, Firebush, salvia (sage), and wild azalea are also examples of nectar plants. When it comes to unwanted pests, it's important to have proper identification of the pest and the plant host, and to take care of the issue promptly. You can often use green measures to tackle the problems. "For example, if you have aphids on your lettuce, try a strong hose, followed by soap solution such as BioWash, then use horticulture oil," said Hughes, who explained that trimming off affected branches, such as with mealybugs on hibiscus, is also an effective measure. If the pests reoccur, then a drench with imidacloprid, a systemic insecticide, can be used. Many natural and organic insecticides actually incorporate plant derivatives. Your local extension office can assist further in helping you choose the right plants. A helpful book on this subject is Carrots Love Tomatoes, by Louise Riotte.