Coleus Pests

Coleus is susceptible to sap-sucking pests, particularly when plants are young or later in the growing season when plants may become stressed and weak from extended hot and humid weather. Mealybugs, Aphids, and Whiteflies are common on indoor and outdoor plants and thrive when plants are grown too close together, overwatered, or overfertilized.

Secondary infestations of pests or diseases are common on plants that are left untreated, eventually leading to neighboring plants being affected and infected as well. Using the least invasive means of treatment first is highly recommended for gardeners who wish to maintain a healthy balance of natural predators and prey in their garden. Often completely removing a heavily damaged plant is the best and least toxic solution over using a broad-spectrum pesticide that does not discriminate between beneficial or parasite insects.

Mealy Bugs

The white or greyish shield shape mealybugs suck moisture and cell material from the foliage and tender stems of Coleus. Adult mealybugs easily overwinter in climates without cold winters or when plants are moved inside to grow as houseplants. Mealybugs do not have a protective shield like a scale insect but they do form a waxy or slightly fuzzy coating that makes using sprays or pesticide powders less effective.

Like other sap-sucking insects, mealybugs produce honeydew when populations get large and can result in sooty mold outbreaks or attract ants to your plants which harvest the sweet sap. Annual plants like Coleus are not typically able to outgrow large colonies of mealybugs which can regenerate up to 6 times during a long, warm growing season. 

Treating Mealy Bugs On Coleus

The most effective way to treat mealybugs is to wipe them off the stems and foliage using a cotton swab dipped in isopropyl alcohol of less than 70% solution strength. The alcohol breaks down the waxy coating and kills any eggs laid in the tight stem and leaf joins. Rinsing the plants with a sharp stream of water will help to clean off any sooty mold build-up or dead insects left behind.

Prune out heavily infested and damaged stems. Move potted plants so there is more air circulation and lightly prune Coleus or other plants in a garden bed.  

Preventing Mealy Bugs On Coleus

Encouraging a healthy ecosystem in your garden or greenhouse is the best protection from excessive mealybug outbreaks. Natural predators include many insects like Lady Beetles, lacewings, minute pirate bugs, and common garden spiders. Birds are also great for helping to reduce populations of sap-sucker insects. Provide natural habitat and food sources like seeds, nectar-filled flowers, and nuts in the garden.

Grow Coleus in its preferred location. Traditionally Coleus was only thought of as a plant to grow in part to full shade although modern cultivars can thrive even in full sun spots.  Weakened plants that are not given their preferred levels of light are always more susceptible to pets and disease and may not be worth rehabbing from a large infestation. 

Aphids

Aphids come in a range of colors from black, white, green, and brown. They primarily feed on the foliage sucking out the plant's nutritious sap, eventually weakening and stunting growth. Leaves will turn brown and die over time or may become twisted a rolled when the female Aphid uses it to protect her eggs. Coleus growing indoors as a houseplant or in a greenhouse, are more likely to be infested year round as the plants are typically grown as an annual outdoors.

Aphids are easily transported by new plant additions to the garden or brought indoors on houseplants grown outdoors for the summer. Aphids are usually very easy to control with very low-tech means although their ability to produce more than one offspring generation a summer will require continued treatments to keep infestations to a minimum.

Treating Aphids On Coleus

Aphids can be easily washed off the undersides of leaves with a sharp stream of water from a hose or a spray bottle filled with tap water. Repeat the treatment daily until no signs of the insect are seen and new growth emerges from any damaged stem ends. Soap sprays and horticultural oil insecticides can also be used as a secondary treatment for large infestations of Aphids.

Always follow the manufacturer's instructions and ensure that your particular plant is listed on the label for treatment. Any damaged plant material should be cut back to reduce the chance of further dieback. Making clean pruning cuts above a set of leaves will help to give the Coleus a natural and bushy shape.  

Preventing Aphids On Coleus

Keeping garden areas free of excess weeds, which often play host to aphids, is an easy way to reduce the chance of infestation for both garden-grown and container-grown Coleus. Encouraging natural predators like lady beetles, hoverflies, green lacewings, or parasitic wasps creates a natural ecosystem environment to keep predators and prey in check.

Larger predators like birds are helpful in reducing aphids and are easy to encourage in your garden by planting native and non-native shrubs and trees that provide both food and shelter. Keeping Coleus plants properly watered helps with overall vigor and health which in turn makes the plants less likely to succumb to any aphid damage. 

Whiteflies

Whiteflies are not true flies and are more closely related to Aphids and other sap-sucking insects. Warm weather and climates with mild year-round temperatures are most likely to have outbreaks of whiteflies in outdoor garden spaces. Typically whiteflies are more of a pest for houseplants and greenhouse-grown seedlings. The small nymph stage is what does most of the damage by sucking out the nutritious sap of the plant's stems and leaves.

Weakened plants will lose leaves or whole stems which turn brown and dieback. The sticky honeydew that whiteflies excrete attracts ants which can grow to be a secondary infestation that is difficult to control. When colonies of whiteflies get large, the adults are easily seen flying when a plant is brushed up against or containers are moved.  

Treating Whiteflies On Coleus

Plants growing in greenhouses or indoors should be monitored regularly for whiteflies. Yellow sticky trap cards do a great job of attracting any flying adults and can be inconspicuously placed near plants in pots or on stakes. When levels of whiteflies become high soap sprays or horticultural oils like NEEM can be used to kill off all stages of Whiteflies and reduce their impact but may not completely get rid of the pest. Heavily infested COleus plants are best removed altogether to prevent damage to neighboring plants. 

Preventing Whiteflies On Coleus

Good cultural practices are the best defense against whiteflies. Indoor plants require good air circulation and lowered humidity levels. Using a gentle fan in the greenhouse to move air or spacing plants so that their leaves and stems do not touch is ideal indoors. Coleus growing outdoors need consistent watering so that they do not become too dry or too wet for extended periods.

Well-draining containers and potting mix are crucial for the overall good health of Coleus.  At the end of the growing season, completely remove plants to reduce the chance of any overwintering eggs or other life stages of the whiteflies. Quarantine any Coleus brought indoors to overwinter as a houseplant and treat if any signs of whiteflies are seen. 

Common Coleus Pests Chart

Sources:

“Coleus”, Clemson University Home and Garden Information Center. www.hgic.clemson.edu