Garden Variety: Prevent pests from harming your indoor plants
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Aphids, mealybugs, scale insects, spider mites and thrips are plant pests that cause significant damage to indoor plants in winter months when left unmanaged. Gardeners have many options for control of these pests but should use caution with home remedies that can cause even more harm to their plants.
These plant pests are small and may go unnoticed as their populations build. They feed by sucking juices from plants, which depletes resources and weakens affected plants over time. In winter, indoor plants are generally stressed from short days, lower light intensity and dry air. The combination of environmental stress and unmanaged pest populations can kill plants over time.
Making sure that plants have the right amount of light and water goes a long way in helping plants withstand pests, but insects and mites can appear even in perfect growing conditions.
Check plants regularly for pests and signs of them. If you observe pests or damage, identify the type of pest and then decide on the best way to manage it based on the species of pest and level of infestation.
Mechanical removal is an option for aphids, mealybugs, and scale insects. Mechanical removal includes squishing, hand-picking, using a tool to gently scrape pests from the plant, washing insects or mites off in a sink or tub, or pruning out infested leaves and stems. Wear latex or nitrile gloves if touching insects is bothersome. Use care to avoid damaging plant tissues in the removal process. A cotton swab or ball dipped in rubbing alcohol may also be helpful in removing mealybugs, scale insects and honeydew excreted by these and other insects.
Spider mites and thrips are more difficult to remove mechanically but rinsing or washing affected plants will remove most of the population. Unfortunately, eggs that wash onto the pot or soil surface will hatch, and the population may start again within a few days. Be diligent in checking plants for insects and mites regularly after an initial infestation is found.
For heavier infestations, or if mechanical removal is not effective, commercial products are an option. Insecticidal soap, horticultural oil, Spinosad, neem, and other botanical products may be safer for indoor use than conventional pesticides. Always read and follow label directions. Also remember that spider mites are not insects and may require different products. More than one application may still be needed because of eggs or pests that survive the product application.
Aphids are small, but they can still be seen clearly with the naked eye. There are many species that come in a range of colors well suited to blending in with plant leaves and stems. They produce honeydew, which drops onto leaf surfaces below where they are feeding and creates a sticky residue on leaf surfaces. They also shed their skins as they grow. Cast-off skins are visible as white flecks.
Mealybugs are white or gray and have a fluffy look because of a soft, waxy coating on their surface. They are about a quarter of an inch long at maturity and hide where leaves attach to stems or branches.
Scale insects range greatly in size and color. The smallest are barely visible, and the largest are the size of an adult lady beetle. Baby scale insects crawl away from their mother to find a feeding location, but they quickly settle in and develop a protective covering. The cover may be soft and waxy or hard like a beetle.
Spider mites are too small to see on leaf surfaces with the naked eye. Their feeding makes tiny white spots on leaves, giving leaves a flecked appearance. When populations are dense, delicate webbing may also be noticeable. Check for mites by holding a white piece of paper under plant leaves and gently tapping the leaves. The mites will be visible on the paper as tiny moving specks.
Thrips are larger than mites but smaller than aphids and are easiest to see with the white paper method described above. Immature thrips are cream-colored or yellow and adults are dark brown to black. They have narrow, elongated bodies. Their feeding gives leaves a silvery, flecked appearance and their waste is visible as black specks. Leaves may also take on a distorted appearance from thrips’ feeding.
Fungus gnats are not really a plant pest because they do not feed on plants, but they may appear with or on indoor plants. They feed on decaying organic matter and live in the potting media. Fungus gnats are a sign that soil is too wet. Reducing the frequency of watering and eliminating standing water in saucers may be enough to eliminate a fungus gnat problem. If they continue to be a nuisance, use a product specific to gnats. Granular products containing Bacillus thuringiensis are a good option.
Homemade soap and water mixtures, baking soda mixtures, hydrogen peroxide and other home remedies may or may not be effective. They could also potentially burn plant tissues in a process called a phytotoxic effect. Varying dyes, fragrances, concentrations and unknown sensitivities of plant types all contribute to the risks.
— Jennifer Smith works in regulatory horticulture and has worked as a horticulturist for various government entities. She has experience in landscape design and maintenance and as an educator.