Being a gardener in Florida is exciting. We have many plants to choose from and the weather is mostly pleasant but always seeming to surprise us. One disadvantage of living in such a place, in addition to having so many growing zones, landscape nurseries, and major shipping ports, is that invasive species that land in Florida don’t like to leave. One newcomer in the lineup of invasive pests is the crape myrtle bark scale (Acanthococcuslagerstroemiae). This invasive insect pest made its way from Texas and, as of a few weeks ago, the only Florida sighting had been in Santa Rosa County. Unfortunately, this pest has now been confirmed in Leon County. Landscapers and gardeners in north Florida should learn how to identify this pest and what options are available for control.
The crape myrtle bark scale, as the name suggests, has a pretty specific host – the crape myrtle (Lagerstroemia spp.). However, in the United States, this scale has also been found feeding on our native beautyberry (Callicarpa americana). Due to the widespread planting of crape myrtles, these should be the gardeners primary focus when looking for this new pest. If present on the tree, it is hard to miss. These scales feed on the bark and are a snow-white color. Being a scale, they produce honeydew that is then covered in black sooty mold. So, if you see a crape myrtle with black branches, look closely and you may see the white scales. If you crush these scales and they leave a pink goo on your fingers, then you very likely have crape myrtle bark scale. Of course, you can send a picture or sample to your local county extension office for confirmation.
Black sooty mold and white scales along the trunk and branches are a tell-tale sign of crape myrtle bark scale. Credit: Mark Tancig, UF/IFAS.
If you do happen to find crape myrtle bark scale in your own landscape, or one that you manage, proper control is important to prevent it from moving along any further. Since scales suck on sap and are protected by an outer shell, systemic insecticides are the preferred product for effective control. These include the neonicotinoids, such as imidacloprid (Merit) and dinotefuran (Safari). The larval stage can be controlled with a horticultural oil, sometimes mixed with another insecticide like bifenthrin (Talstar), however, this will not control the adults. Another option is to completely remove the tree and burn all of the plant material.
Excessive sooty mold has turned these branches black. Be on the lookout for crape myrtles looking like this to help identify crape myrtle bark scale. Credit: Jim Robbins, Univ. of Ark. CES. Retrieved from bugwood.
The crape myrtle bark scale can significantly reduce the aesthetic value of crape myrtles due to the black sooty mold that covers the bark. It is also known to reduce flowering and can lead to thinning of leaves. Since crape myrtles make up a big part of our managed landscapes, let’s all work together to scout for this pest and control it when found. If you have questions, please contact your local county extension office.
Difference in flowering due to crape myrtle bark scale damage. Credit: Jim Robbins, Univ. of Ark. CES. Retrieved from bugwood.
There are lots of plant pests out there, and it can take a trained eye to tell which one is doing damage. Many of the insect pests that feed on crops and ornamentals have piercing-sucking mouthparts. These insects do not chew on leaves and leave holes behind; instead, they have a long stylus-like mouthpart they use like a straw to suck out plant juices. Over time this can weaken plants, cause irregular growth as damage builds up on new sprouts, introduce diseases to their hosts, and even cause mold to grow on leaves.
Because they drink so much fluid for their meals, many piercing-sucking insects exude a sugary liquid called honeydew. This liquid drops onto stems and leaves below which can leave them shiny and sticky. Eventually, the coating will grow a light greyish coating of sooty mold, which doesn’t do much harm to the plants itself but is a good indicator that you have an insect problem. You may also notice ants on your plants, working to harvest the honeydew for food. The ants don’t harm the plant, but following are some of the pests that do:
Aphids feeding on a plant stem.
A parasitic wasp emerging from a dead aphid.
Aphids – Found on a wide variety of plants, aphids are fat-bodied little insects that often focus on new, tender growth. Their color depends on the plant they’re feeding on, and they can breed explosively. A female aphid does not need to mate to produce offspring, so a one can produce a lot of children very quickly. Look closely and you might be able to see their cornicles, which look like little tailpipes; these can help identify these pests. Luckily, we have some help in controlling aphids, as they are often parasitized by wasps. If you see large, swollen, brown aphids present, you probably have some wasps working for you.
Ants tending some scale insects on a stem.
Scale Insects – Sometimes appearing to just be a bump on a stem or leaf, scale insects don’t move once they pick a plant to live on. Prolific producers of honeydew, some species grow a waxy shell which can protect them and make them difficult to deal with.
A mealybug.
Mealybugs – If you spy something white and fluffy living on stems or leaves, you might have mealybugs. Soft-bodied insects that are related to scales, they don’t move much. They feed on a wide range of host plants, but can effectively be controlled with a variety of methods once they’re found.
Whiteflies on the underside of a leaf.
Whiteflies – Not true flies, they are truly white in color. Tiny little members of the order Hemiptera (the same order that includes, aphids, scales, and mealybugs), they hang around the undersides of leaves. They enjoy warm weather and can become a problem in greenhouses. They are a bit more difficult to control than some of the other pests listed here.
A psyllid nymph hiding in its waxy coating.
Psyllids and planthoppers – Small jumping insects that affect a variety of plant species, some are responsible for transmitting important plant diseases. Pierce’s disease of grapes and citrus greening, for example, are both vectored by these critters. Young nymphs sometimes secrete a waxy coating which may make them look similar to mealybugs.
A tiny two-spotted spider mite.
Spider Mites – Not an insect but an arachnid, spider mites love hot, dry weather. Almost microscopic in size, the damage they do to leaves is often the first sign that they are present. Looking closely, one might notice tiny webbing where the mites live, or even the mites themselves on the undersides of leaves and on stems.
Many of these pests can be treated with a combination of methods. A sharp jet of water can dislodge some, hand removal can reduce populations even more, and products such as insecticidal soap or horticultural oils can finish them off. Insecticidal soaps are best used on soft-bodied insects such as aphids or mealybugs, while oils such as neem can help suffocate hard scales. Use products such as horticultural oil in the evening during hot weather to avoid damaging plant tissues with intense sunlight. Thorough coverage is important, as these products only control the pests they contact.
Crapemyrtle bark scale are often found in branch crotches and wounds to the bark. Photo credit: Gary Knox, UF/IFAS.
There is a new pest in the western panhandle of Florida. Crapemyrtle bark scale (CMBS) is a scale that is found on the trunks, branches, and twigs of crapemyrtle. It is the only known scale insect found on the bark of crapemyrtle. There are other scales that occur on the leaves.
When scouting for this pest, look for very small (2 mm or 0.08 inch) white or light gray spots on the bark of crapemyrtle. The adult females do not ever move once they have found a place to feed and reproduce. Under her protective covering, she lays eggs that hatch into ‘crawlers’ that then crawl away to find their own spot to settle down. When squished, they exude a pink goo (the eggs or newly hatched crawlers). Males are winged and travel to find their mates. See this comprehensive information on their interesting biology.
While the scale does not outright kill the trees, it lessens their landscape value and can reduce flowering. And like other scale, CMBS secretes lots of honeydew; black sooty mold then feeds and grows on the honeydew. The black sooty mold does not harm the plants directly, but it is unsightly and can interfere with photosynthesis if present on the leaves.
Crapemyrtle bark scale are white to gray and ooze pink when squished. Photo credit: Gary Knox, UF/IFAS. ,
Unfortunately, CMBS has also been found on a very popular native bush, American beautyberry, Callicarpa americana, and it is yet unknown whether CMBS will expand its host range to other plant species in our country. In Asia, this pest has been found on some economically important crops like pomegranate and persimmon.
CMBS is a tough insect to control. And it is best left to the professionals. Dr. Adam Dale, an entomologist at the University of Florida, recommends using pyriproxyfen (in the product Distance) or buprofezin (in the product Talus). These are insect growth regulators that have shown to provide great control of CMBS and other similar scale insects on trees and other woody plants. Although these products are not systemic, they are translaminar, which helps increase their control and reduce any non-target effects on beneficial insects like bees. Two applications 7–14 days apart are suggested. However, these products can only be applied by licensed pest control applicators.
Severe infestation of crapemyrtle bark scale and sooty black mold. Photo credit: Gary Knox, UF/IFAS.
Systemic insecticide drenches are effective but pose a dangerous hazard to bees and other pollinators as the poison also gets into the flower nectar. The product labels prohibit application of these type of products to flowering plants for that very reason.
Routine close inspection of your crapemyrtle trees is critical for CMBS control. Early treatment will help prevent heavy infestations as seen in some of the photographs. When pruning your crapemyrtles, thoroughly clean your tools between plants to prevent any accidental spread.
Prevent this scale from coming into your landscape in the first place. Inspect all new plants you are considering adding to your landscape for any sign of CMBS or other insect or disease presence.
Scale insects on a cabbage palm (Sabal palmetto). Photo Credit: Matt Lollar, University of Florida/IFAS Extension – Santa Rosa County
This week I was on a couple site visits to look on some cabbage palms (Sabal palmetto) and some banana shrubs (Michelia figo). The palms had a white, waxy substance on their frond petioles and the banana shrubs had white specs on the tops of their leaves. Upon further investigation, I realized the waxy substance and specs were both different species of scales. Scale insects are serious pests of a number of ornamental plants. Here in Florida there are 13 different families of scales with the most common being armored scales, soft scales, and mealybugs. Scales have piercing-sucking mouthparts which they use to siphon fluids from the leaves, stems, and sometimes roots of many ornamental plants. Heavy infestations cause extensive leaf yellowing, premature leaf drop, branch dieback, and eventually plant death.
Scale Biology
The life cycle of a scale begins with eggs being laid beneath wax coverings or beneath the adult female. Eggs typically hatch in 1 to 3 weeks. The newly hatched nymphs, called crawlers, move around a plant until they find a spot to feed. Once a feeding site is located, their piercing sucking mouthparts are inserted into the plant and the crawlers begin to feed and grow. The males of many scale species develop wings as adults and fly to other plants to reproduce.
Magnolia white scales on a banana shrub (Michelia figo). Photo Credit: Matt Lollar, University of Florida/IFAS Extension – Santa Rosa County
Armored Scales
Armored scales get their armor by secreting a waxy covering over their bodies that is not attached. The scale lives under this covering and uses it as a protection to feed under. Armored scales can be almost any color or shape and range anywhere from 1/16 to 1/8 inch in diameter. For females, these shapes range from circular to oval to long and slender. The males typically have coverings that are more elongate and smaller than the females. As adults, the males are tiny, winged, gnat-like insects and are rarely seen.
Gloomy scale (Melanaspis tenebricosa) with armored covering removed. Photo Credit: A. G. Dale, University of Florida/IFAS
Soft Scales
Similar to armored scales, soft scales secrete a waxy covering, but it is attached to their bodies. Soft scales can be a number of colors, shapes, and sizes and range anywhere from 1/8 to 1/2 inch in diameter. Their shapes vary from spherical to nearly flat.
Population of adult and immature tuttle mealybugs (Brevennia rehi) on a blade of zoysiagrass. Photo Credit: Lyle J. Buss, University of Florida/IFAS
Mealybugs
Mealybugs are soft-bodied insects that possess a covering of flocculent, white, waxy filaments. They are about 1/8 inch in length and usually pinkish or yellowish in color. Mealybugs have piercing-sucking mouthparts which they use to siphon fluids from the leaves, stems, and sometimes roots of many ornamental plants. Mealybug damage produces discolored, wilted, and deformed leaves.
Scale and Mealybug Management
Cultural Control – Plant inspection prior to purchase or installation is the first line of defense against a scale or mealybug population. Make sure to inspect the undersides of leaves and plant stems. Infested sections of plants can be pruned and plant material should be cleaned from the planting area and discarded. Also, you can increase air flow and decrease humidity by proper installation and pruning. Over-fertilizing can also increase pest populations.
Larva of a brown lacewing. Credits: Lyle Buss, University of Florida.
Biological Control – Predators, such as ladybugs and green lacewings, are usually present in large enough numbers to suppress scales and mealybugs to a desirable threshold. However, broad-spectrum insecticides and bad weather can reduce predator numbers. Look for signs of predation by inspecting dead scales for jagged holes in their waxy coatings. If predation signs are present, use more selective chemical controls and oils as opposed to broad-spectrum products.
Chemical Control – Timing is everything when it comes to managing scale and mealybug insects. Crawler activity is more pronounced with the flush of new plant growth in the spring. Before application, prune infested plant parts off first to promote greater penetration of insecticides into the foliage. Dormant Oils are often used in the winter to smother scale insects. These are good choices to implement because they don’t harm non-target or beneficial insects. Care must be taken to read the label and use them at the correct temperature, since use in hot weather may burn foliage. Contact products (acephate, bifenthrin, carbaryl, etc.) must be applied to inhibit the crawler stages of these insects and systemic products (acetamiprid, imidacloprid, thiamethoxam, etc.) can be used on the sessile growth stage. Plants should be sprayed thoroughly to the point of drip or “run off” from leaves, twigs, and stems. Repeated applications may still be necessary even if the timing is right, as crawler populations are often large and crawlers like to hide under old waxy scales. Systemic drenches are also a viable option. With good spray coverage, horticultural oils can kill scales at all stages of growth. Refer to the product label for phytotoxicity and temperature guidelines. Even after successful treatment, the outer coatings of the scales may remain on the plant material for weeks, which can be unsightly. The best way to determine if scales are dead is to squeeze them. They will be dry when squeezed if they are dead and they will ooze liquids if they are living (they were at least alive to the point of being squashed).
For insect identification and additional information on scale control, please see:
A couple weeks ago, I was on a site visit to check out some issues on Canary Island Date Palms. The account manager on the property requested a site visit because he thought the palms were infested with scale insects. He noticed the issue on a number of the properties he manages and he was concerned it was an epidemic. From a distance, lower fronds were yellowing from the outside in and the tips were necrotic. These are signs of potassium deficiency with possible magnesium deficiency mixed in.
Transitional leaf showing potassium deficiency (tip) and magnesium deficiency (base) symptoms. Photo Credit: T.K. Broschat, University of Florida/IFAS Extension
Nutrient deficiencies are slow to correct in palm trees. It’s much easier to prevent deficiencies from occurring by using a palm fertilizer that has the analysis 8N-2P2O5-12K2O+4Mg with micronutrients. Even if the palms are part of a landscape which includes turf and other plants that require additional nitrogen, it is best to use a palm fertilizer with the analysis previously listed over a radius at least 25 feet out from the palms. However, poor nutrition wasn’t the only problem with these palms.
Upon closer look, the leaflets were speckled with little bumps. Each bump had a little white tail. These are the fruiting structures of graphiola leaf spot also known as false smut.
Graphiola leaf spot (false smut) on a Canary Island Date Palm. Photo Credit: Matt Lollar, University of Florida/IFAS Extension – Santa Rosa County
Graphiola leaf spot is a fungal leaf disease caused by Graphiola phoenicis. Canary Island Date Palms are especially susceptible to this disease. Graphiola leaf spot is primarily an aesthetic issue and doesn’t cause much harm to the palms infected. In fact, the nutrient deficiencies observed in these palms are much more detrimental to their health.
Graphiola leaf spot affects the lower fronds first. If the diseased, lower fronds are not showing signs of nutrient deficiencies then they can be pruned off and removed from the site. All naturally fallen fronds should be removed from the site to reduce the likelihood of fungal spores being splashed onto the healthy, living fronds. A fungicide containing copper can be applied to help prevent the spread of the disease, but it will not cure the infected fronds. Palms can be a beautiful addition to the landscape and most diseases and abiotic disorders can be managed and prevented with proper pruning, correct fertilizer rates, and precise irrigation.
