Although most Verbena plants are easy to grow and require little maintenance, they can be host to a wide range of pests in the garden. Annual varieties and perennial types can suffer from infestations of sap-sucking insects like aphids, mealybugs, spider mites, and lace bugs when they are grown with too much “love”.
Overwatering, over-fertilizing, and growing in overcrowded conditions become stressed and attract opportunistic insects. Caterpillars are a nuisance that reappears yearly during roughly the same part of the summer, making control easier when anticipated in advance.
Green Peach Aphids (Myzus persicae)
Aphids of all types are sap-sucking insects that feed on the moisture inside foliage that the host plant uses to transport nutrients from root to tip. Green Peach Aphids are the most common type of Aphid to feed on Verbena and are common pests for a wide range of plants, not just peach trees. The insect is small but easy to see with its bright greenish-yellow coloring.
The aphid causes physical damage to the foliage and tender new growth of stems. It is also a vector for viruses that affect a wide range of edible and ornamental plants. The Aphids are found on the undersides of the leaves and lay eggs in stem and leaf joins which makes it more difficult to eradicate all generations with a single treatment.
Treating Green Peach Aphids On Verbena
Early infestations of aphids are easily treated by washing them off the plant with a sharp stream of water from the hose. Repeated treatments may need to be done every few days until no further damage is seen. Horticultural soap sprays may be needed to clear a larger infestation. Follow all instructions on the label and make sure the product you use is labeled for use specifically on Verben. Spray the top and bottom of the leaves until the soap runs off.
Annual Verbena that is heavily infested may need to be removed and disposed of to prevent spreading the Aphids to other plants.
Preventing Green Peach Aphids On Verbena
Verbena which has plenty of sunshine and air circulation will grow healthy and strong and be better at resisting attacks by APhids. Overfetilizing often encourages quick, tender growth that is dense and favored by any type of sap-sucking insect. Apply fertilizers only when absolutely necessary.
Avoid under-watering or over-watering verbenas in the garden as stressed plants are much more susceptible to insect attacks. Practice good garden hygiene by removing infected plant material as quickly as possible and thoroughly clearing any top growth from perennials that have been infected at the end of the growing season to reduce populations of pests from overwintering.
Caterpillars
Several caterpillars prefer to feed on the leaves of Verbena. All types show the same signs of damage and infestation but appear at different times during the growing season and are often regionally specific. Some of the most common caterpillars to look out for are wooly bear, Bud Moth, and Sand Verbena moth.
Photo by Michele Dorsey, unedited, Flickr, Copyright CC BY 2.0 DEED
Damage is typically on the leaves and softer, new stems. Moths lay their eggs on the host plant where all stages of the caterpillar will feed, grow, and eventually pupate into the adult form. This process can take anywhere from a few days to a few weeks with most moth species. Damage can be outgrown on perennial types of Verbena but may be detrimental to the health of annual and tender perennials grown as annuals.
Treating Caterpillars
Hand-picking is the best way to control large amounts of caterpillars. Deposit the larva in a bucket of soapy water to kill it before adding it to the trash. Remove damaged stems to control any dieback on the plant. Sprays to control caterpillars are not recommended for the home gardener as they are rarely effective for control and tend to be broad spectrum often harming beneficial predators as well as the “pest”.
Preventing Caterpillars
Provide other plants that provide food, shelter, or housing material to attract natural predators such as birds and smaller mammals to your garden. Remove weeds that are likely to overwinter and host immature stages of the caterpillar. Removing damaged plant material in the fall will ensure that no life stage of the moth overwinters to begin a new lifecycle the following growing season.
Verbena Leafminer (Agromyza artemisiae)
Leafminers are a type of fly that lays eggs inside the layers of foliage to protect the immature larval stage. As the larval stage grows they “mine” tunnels in leaves which are visible as twisting and turning lines that are random and do not break the surface of the leaf. Many generations of leafminers form during long growing seasons as they move between host plants after pupating.
Damage to a mature perennial verbena is rarely catastrophic and almost entirely cosmetic. Plants will recover when new growth emerges later in the summer or the following growing season. Annual types may have a decline in overall plant health due to large numbers of leafminers disrupting the process of photosynthesis in the leaves.
Treating Verbena Leafminer
Treatment involves simply removing any foliage that has the telltale random tracking. No sprays or other treatments are effective at reaching the larva inside of a leaf structure. Pruning out affected material effectively breaks the life cycle. Make the cut just above a set of leaves, well below the damaged section, to encourage bushy new growth and flowering.
Preventing Verbena Leafminer
Vigorously growing plants that are well watered consistently through the growing seasons are able to withstand an attack from leafminers and are less attractive to most pests in general. Leafminers typically only cause cosmetic damage that is easily removed, allowing the plant to recover quickly. Make sure your plant is in a location that has full sun exposure or only 4 hours or less of shade.
Fertilize Verbena lightly and only when necessary like when they grow in a planter or hanging basket. Plants growing in a garden bed thrive with an all-season slow-release feed like organic compost mulch around their root zone.
Lacebugs
Lacebugs come in a wide range of species and are typically plant-specific. The lacewings that thrive on Verbena are drawn to plants in the heather family, feeding and laying eggs on the underside of leaves. The characteristic molasses-like spots on the undersides of leaves protect the eggs until hatching but can be a nuisance when infestations are large and left untreated.
Plants that decline in growth or flowering during the hottest parts of the summer should be checked for Lacewing signs. Secondary infestations of aphids or mealy bugs are common when plants are not treated as well as outbreaks of sooty mold from the sticky deposits left by the females.
Treating Lacebugs on Verbena
Small amounts of lacewings can be rubbed off the foliage with a gloved hand. Spraying with a strong jet of water from the hose can be effective at washing the pests off. Repeat this treatment many times until there are no more signs of the eggs or adults. Interrupting the life cycle will stop further damage and allow the plant to recover. Prune out affected stems and foliage strategically to ensure that the regrowth looks natural. Make sure to make pruning cuts directly above a set of leaves for the best plant shape.
Preventing Lacebugs on Verbena
Choose cultivars of Verbena that are resistant to lacebugs, especially if you garden in a climate that has summer temperatures regularly above 90F (32C). Reduce the use of broad-spectrum insecticides in your garden. These products kill all bugs, beneficial or parasitic, and disrupt the balance of native ecosystems. Plant shrubs and other plants attract local predators including beneficial insects and birds which regularly feed on the lacebugs.
Over-fertilizing results in rapid and lush top growth that often weakens the plant and is very attractive to lacebugs and other sap-sucking insects. weakens the plant and is very attractive to lacebugs.
Spider Mites
Spider mites are more common in climates that have hot temperatures through the summer and relatively low humidity. The small, red arachnid sap-suckers feed on the undersides of leaves giving the top a stippled or mottled appearance. Because the mites are almost impossible to see with the naked eye, infestations can continue to multiply showing very few symptoms until the leaves start to turn brown and fall off. As the populations grow they form webs between leaves and in the joints of the stems.
Mature plants typically can tolerate light outbreaks of spider mites and will only drop a few affected leaves. Seedlings or annual types of Verbena can be impacted more, making removal and disposal the only option to treat the plants.
Treating Spider Mites on Verbena
Removing affected foliage is the quickest way to treat spider mites. This is a viable option for light infestations. Heavy outbreaks will need to be treated with selective soap sprays or a horticultural oil that contains NEEM or other organically approved oil. Broad-spectrum insecticides typically encourage outbreaks of spider mites by killing off beneficial predators in addition to the pests. Predatory mites can be introduced into a closed environment like a greenhouse to help keep spider mites to a minimum.
Preventing Spider Mites on Verbena
Spider mites thrive in dry and hot locations and seek out plants that are stressed by these conditions. Keep Verbena growing healthy and strong with consistent watering and fertilizing only when absolutely necessary. Encouraging beneficial insects, birds, and other small mammals to your garden helps to balance your particular landscape ecosystem which in turn helps to control populations of any pests and diseases.
Mealybugs
Mealybugs are sap-sucking insects that cause damage to the foliage and tender stems of Verbena. Much like aphids, mealybugs disrupt the way plants photosynthesize and transport nutrients. The individual insects are easy to see and usually are found on the bottom sides of leaves or stem joints.
Shield-shaped and ¼ of an inch in length, the insects grow a wooly or waxy protective coat making large infestations look like residue on plants. The female lays eggs in clusters protected with a waxy coating which makes it difficult to treat effectively. Secondary issues like sooty mold or ant infestations happen as a result of heavy honeydew secretions.
Treating Mealybugs on Verbena
Mechanical or biological controls are sufficient to reduce infestations to levels that are tolerable or almost non-existent. A cotton swab soaked in isopropyl alcohol is great for removing the insects and clusters of eggs. Mealybugs that are on exposed parts of the plant can be washed off with a sharp spray of water from a hose.
Remove heavily infested branches by pruning well below the damage and dispose of them in the trash. Encouraging natural predators such as lady beetles, minute pirate bugs, or parasitic wasps helps to keep levels of predator and prey balanced and outbreaks relatively unnoticeable.
Preventing Mealybugs on Verbena
Provide plants for beneficial insect and bird predators in your garden. Native shrubs that produce berries, nuts or have dense branches for shelter are an easy way to start encouraging wildlife to frequent your landscape. Discontinue the use of broad-spectrum insecticides in your yard. These sprays and preparations affect all of the insects, not just the bad guys.
Remove infected plant material as quickly as possible to prevent mealybugs from spreading. Ensure that any new plants brought into your garden do not have signs of pest damage like discolored or dead leaves, or white/greyish mealybug coating on stems.
Common Verbena Pest Chart
| Pest | Identifying | Treating |
|---|---|---|
| Green Peach Aphids | small, green insects on the underside of leaves and in stem joins, yellowing or stunted leaf growth, distorted and twisted foliage used to hide the adult insects | Sharp stream of water from the hose, horticultural soap sprays labeled for use on Verbena |
| Caterpillars | Flower buds and developing seed pods are distorted and destroyed by the larval stage, chewed and ragged foliage, stem tips removed | Pick visible caterpillars off the plant and dispose in soapy water, prune all spent top growth and dispose of them to remove any possible overwintering caterpillars |
| Verbena Leafminer | Tunnels visible between the top and bottom layers of the leaves | Remove affected foliage, and remove all spent top growth in the fall to prevent overwintering of any stage of the insect, plant-resistant varieties |
| Lacebugs | Sticky black or brown spots on the undersides of the leaves, yellow stippling on the top sides of the leaf, browning, and foliage death from the tips of the plant toward the base. | Practicing good garden hygiene in the fall to prevent overwintering, remove any affected stems or foliage, horticultural oil can be used early in the spring on perennial plants |
| Spider mites | Yellow or grey stippling of the top or undersides of leaves, webbing on the undersides of leaves and in the stems joins, most common late in the summer in locations with extremely dry summers | Good garden hygiene, good watering practices to keep the plants from becoming stressed. Insecticidal soap on perennial types |
| Mealybugs | Clusters of white or greyish shield-shaped insects on the stems and undersides of the leaves, distorted and stunted foliage growth at the tips of the plant, sooty mold on leaves as a result of honeydew secretion | Good garden hygiene, plenty of sun exposure, horticultural soap spray |
Sources: “Lantana and Verbena”, Texas A&M Extension. www.gillespie.agrilife.org