Scale insects on plants

Scale Bug – How To Control Plant Scale

Scale is a problem with many houseplants. Scale insects suck sap from plants, robbing them of essential nutrients. Let’s learn more about identifying scale and how to control them.

Identifying Scale Plant Insect

Scale insects thrive in warm, dry environments. The scale bug is small, oval and flat, with a protective tan to brown shell-like covering (scale). Scale generally targets the undersides of leaves and around leaf joints.

The scale plant insect consists of three types:

  • armored scale
  • soft scale
  • mealybug

Scales, both armored and soft, are the most destructive. Armored scales are more difficult to control once mature. Soft scale bugs excrete large amounts of honeydew, which encourages the growth of sooty mold, a black-colored fungus that interferes with photosynthesis. Mealybugs are easier to control. Scales cannot fly so, dispersal depends on the movement of crawlers. Crawlers may be detected by placing double-sticky tape on plant branches.

Scale Insect Control

Scale-damaged plants look withered and sickly. Leaves turn yellow and may drop from the plant. They may also have sticky sap or a black fungus on the leaves and stems. Heavily infested plants produce little new growth. If scale insects are not controlled, death of

infested plants is possible. Scale insects are invasive and will infest other plants, so move infested plants away from healthy ones.

Several well-known remedies can be used to eliminate scales from a houseplant. However, there is no easy cure for a scale bug infestation. One possibility is to pick off or gently scrub them loose from the leaves and stems. Dabbing each scale with an alcohol-soaked cotton swab is another possibility for lightly infested plants.

There are also numerous chemical products available for the control of scale bugs. Insecticide sprays, like neem oil, are available at garden centers. Spray applications should be timed to coincide with the crawler stage, which is most susceptible to insecticides. Insecticides must be applied thoroughly each week for a month or more for the greatest results.

For heavy infestations, it is sometimes best to throw away infested plants.

Homemade Control of Plant Scale

Many people prefer to use homemade control of plant scale. Insecticidal soap is a safe and effective alternative to conventional insecticides. You can use bleach-free dishwashing liquid (1 1/2 teaspoons per quart or 7 mL per liter of water) in place of commercial insecticide soaps. Homemade control of plant scale can also be achieved with oil spray. Mix 2 tablespoons (29.5 mL) of cooking oil and 2 tablespoons (29.5 mL) of baby shampoo in 1 gallon (1 L) of water. This can also be mixed with 1 cup (236.5 mL) of alcohol to help penetrate the insect’s shell.

If a fungus is also present, add 2 tablespoons (29.5 mL) of baking soda. Shake well before and during application. Spray every five to seven days as needed, covering both sides of the foliage. Wash the leaves individually with the soap/oil mixture and rinse well.

BEFORE USING ANY HOMEMADE MIX: It should be noted that anytime you use a home mix, you should always test it out on a small portion of the plant first to make sure that it will not harm the plant. Do not spray on hairy or waxy-leaved plants. Also, avoid using any bleach-based soaps or detergents on plants since this can be harmful to them. In addition, it is important that a home mixture never be applied to any plant on a hot or brightly sunny day, as this will quickly lead to burning of the plant and its ultimate demise.

When you find scale on plants, getting rid of them can take some time – but it’s not impossible! In this post, I will show you exactly how to get rid of scale on houseplants, FOR GOOD. Simply follow these organic houseplant scale treatment methods.

Sometimes it feels like all of the plant bugs on the planet are trying to attack my houseplants! Until a few years ago, I’ve never had to deal with houseplant scale before.

I have no idea where they came from, but one day I suddenly noticed a scale insect infestation on my goldfish plant. Gross!

But don’t worry, scale is not a death sentence for your plants! I’ve successfully descaled my houseplants, and so can you!

What Are Scale Insects?

Houseplant scale are gross looking things that suck the sap out of the leaves and stems of plants; resulting in stunted or deformed leaf growth, yellowing of the leaves, brown pock marks, and possibly leaf drop.

You will usually find houseplant scale hanging out on the stems and leaf joint of an infested houseplant, and along the veins of the leaves, but you could find them anywhere on a plant.

You may also notice sticky leaves on houseplants, on their pots, or around the area where the plant is sitting.

Sometimes this is one way to help with plant scale identification if you’re unsure. As they feed, scale insects excrete a sticky residue which is a common sign of an infestation.

What Does Scale Look Like On Plants?

Scale insects are very difficult to see on a plant. Even if you do notice them, scale bugs on houseplants look more like a weird growth than a bug.

They look like small brown dots or bumps, and they don’t move. Eek! To me, they look like scabs on a plant (and that’s seriously what I thought they were the first time I saw them, haha!).

They can be rounded, oval shaped or flat, and can range in size from barely visible to large bumps on a plant. Their color can range anywhere from brown to tan to white.

If the bugs on your houseplants are white and fuzzy and look more like mildew, those are mealybugs. Here’s how to get rid of mealybugs.

Scale bugs on plants like to cluster, so they are very noticeable once the population gets large. Like I said before, they don’t look like bugs so you probably won’t even notice them until your plant has become infested.

Different stages of scale insect life cycle

Houseplant Scale Insect Life Cycle

There are several stages to the scale insect life cycle, and the entire cycle takes about 7-10 weeks. It takes a few weeks for the eggs to hatch into nymphs (aka scale crawlers), and then another 6-9 weeks for the crawlers to mature into adults.

A scale crawler can move around on a plant (or migrate to surrounding plants!) and, once they find a good place to start feeding and mature into adults, they never move again.

Scale insect eggs and nymphs are tiny, so it’s easy to understand why most people will never know their houseplant has scale until the population has exploded.

Scale Damage On Plants

Scale insect damage can look like pock marks on plants like succulents and cacti, or it can be something as subtle as brown or yellow leaves on a plant.

Thankfully, the damage caused by scale insects is not as quick to occur or as devastating as it is with spider mites, but it can still look pretty bad.

If a houseplant scale infestation goes left untreated, the plant will eventually die; although it would take a long time, and a very large scale population for them to kill a large houseplant.

Related Post: How to Get Rid of Fungus Gnats In Houseplants Soil

Scale insect damage on cactus plant

Where Do Scale Bugs Come From?

When you discover scale on plant leaves, the first question you’ll ask is where the heck did they come from? Scale insects are very sneaky, and many times you will never figure out where they came from.

Indoor plant bugs can come from anywhere, so don’t go crazy trying to figure it out what causes scale on plants. But, here are a few of the most common places where they may have come from…

  • A brand new houseplant that you recently brought home from the store
  • Contaminated potting soil
  • Reusing a dirty plant pot
  • Moving your houseplants outside during the summer
  • Fresh produce or cut flowers from the garden (or even from the grocery store!)
  • An open window – the crawlers are tiny, so you never know!

Read more about how houseplants can get bugs here.

Houseplant scale and damage on my cactus plant

How To Get Rid Of Scale Insects On Houseplants

As with any plant pest infestation, when you find scale insects on plants, you will want to isolate the infested plant and begin treatment immediately.

I don’t recommend using a chemical scale pesticide, because houseplant scale are resistant to most pesticides.

They also have the ability to develop a resistance to any chemical pesticides they are exposed to on a regular basis. Plus, in most stages of their life cycle, pesticides won’t penetrate their hard outer shell anyway.

So keep your family and pets safe, and skip the toxic chemical pesticides on your houseplants. Below are some methods you can try that work great to treat houseplant scale insects.

You can learn even more about all-natural houseplant pest control remedies here.

How To Treat Scale On Plants

One way to kill and remove as many of the scales from the plant as you can is by using a cotton swab dipped in rubbing alcohol (you may need to pry some of them off using your fingernail).

In order for rubbing alcohol to be effective, it must come in direct contact with the scale insects.

This scale bug treatment method works very well for small infestations, and to get rid of as many of the large scale insects that you can so you can gain the upper hand.

As you work on removing scale from plants, be sure that you check every crevice of the plant, around the leaf and stem joints, and underneath all of the leaves.

They like to hide, so be sure to check the plant from a bunch of different angles too.

Also brush away a little dirt around the base of the stem to see if any are hiding there, scale insects could also be found on the roots of the plant.

Use rubbing alcohol to kill scale on houseplant

Make Your Own Homemade Scale Insecticide Soap

You could buy organic insecticidal soap, or you can make your own homemade insecticide for houseplants.

The plant scale spray recipe I use 1 tsp of organic mild liquid soap per 1 liter of water. Then spray it directly on the scale and on the leaves of your infested plant.

If your plant is small, you can bring it to the sink or shower and wash the leaves with this soap and water solution, gently removing as many of the scale as you can as you wash the plant.

Keep in mind that some types of soap can damage plants, so it’s best to test any type of spray on a couple leaves before you spray the entire plant.

Homemade scale insect killer insecticide soap

Using Neem Oil For Scale On Plants

Neem oil for houseplants is a natural insecticide for indoor plants, and it’s very effective for treating scale on houseplants. An added bonus is that neem oil has a residual effect to help with future pest prevention too.

You can buy neem oil concentrate for pretty cheap, and a bottle will last you a long time. If you do end up getting the neem oil concentrate, then you’ll need to mix it with a little bit of mild liquid soap to help the oil mix with water. Don’t worry, it’s easy, just follow the instructions on the label.

You can use a pre-mixed horticultural oil or hot pepper wax spray instead of neem oil as a plant scale treatment, and these also work very well to help get rid of scale insects.

Learn more about neem oil insecticide

Using neem oil insecticide for scale insects

More Tips For Getting Rid Of Scale On Plants

You can’t treat a plant once and expect to get rid of scale insects for good, you need to be persistent. Keep checking your plants a few times a week, and remove any new bugs that you see. Here are a few additional tips…

  • Scale can hide in the soil of a houseplant, so if a plant is plagued by recurring infestations, you could try removing the top inch of dirt from the pot and replacing it with fresh potting soil.
  • Crawlers can leave the plant, and then come back to infest it again. So remove the plant from the area and clean any crevices where plant pests could be hiding. Be sure check around the outside lip and inside edges of the pot and plant tray, and also the bottom of the pot for hiding scale insects.

  • Trim any heavily infested leaves from the plant and toss them into the trash (outside of your home). Never trim all the leaves from a houseplant though.
  • If you decide to repot a plant after treating it for scale, then be sure to sterilize the pot before reusing. Houseplant scale insects can hide on the edges or the rim on a plant pot, and can easily infest any plant that’s potted in there. Scrub the pot with soapy water, or better yet, put it in the dishwasher to sterilize it.
  • Use a neem based leaf shine, a natural insecticide for houseplants, regularly until you are sure you plant is scale-free.

It’s hard to get rid of scale on houseplants the first few times you try, it will take several treatments. Even if you are able to kill all of the adults, the eggs and babies are tiny and easily overlooked.

There’s no doubt that fighting scale on indoor plants can be super frustrating, but it’s worth it to save your favorite houseplants.

If you’re struggling to get rid of bugs on indoor plants, my Houseplant Pest Control eBook is for you! It will show you exactly how to get rid of bugs on houseplants naturally, including houseplant pests identification, home remedies for plant insects, how to keep houseplant pests from EVER coming back, and much more!

Products I Recommend

Recommended Reading:

  • Winter Houseplant Care
  • The Complete Houseplant Survival Manual
  • The House Plant Expert

More About Houseplant Pests

  • Organic Plant Pest Control Supplies
  • How To Get Rid Of Thrips On Houseplants
  • How To Debug Plants Before Bringing Them Indoors
  • How To Get Rid Of Spider Mites On Houseplants, For Good!
  • How To Get Rid Of Whiteflies On Indoor Plants, For Good!
  • How To Get Rid Of Bugs On Houseplants

How do you get rid of scale on houseplants? Share your scale insects treatment tips in the comments below.

Various stages of soft scales attended by ants.

Scale insects are a large and diverse group (about 8,000 described species) in the superfamily Coccoidea of the order Hemiptera, closely related to aphids and whiteflies, but they look quite different from your typical insect. These small insects vary a lot in size (from 1/16 to 3/8 inch across) and appearance but all grow beneath a wax covering that resembles an individual reptile or fish scale, hence the common name. This covering which protects the insect underneath it may be a flattened oval, dome-shaped, oyster shell-shaped, resemble small mussels, or have a fluffy coating.

A gnat-like male scale (Dactylopius sp.).

Female scales, usually immobile, are wingless and often with no visible legs or antennae and don’t even look like an animal. The seldom seen male scale looks somewhat like a tiny gnat, but doesn’t have mouthparts and cannot feed. Some species are hemaphroditic while others reproduce by parthenogenesis. Females lay eggs under their bodies which hatch into the first instars, called crawlers, which do have legs and are mobile.

Cottony cushion scales infesting a citrus tree.

Usually smaller than a pinhead, in general they move around searching for a favorable spot to settle down to feed and begin producing their distinctive scale coverings, but in some species they are moved by wind to settle on other plants. When they molt to the next instar almost all female scales lose their legs and are sedentary as adults; only a few species have the ability to move after the crawler stage.

Yellowish coffee green scales produce a sweet, sticky liquid called honeydew. The substance is a food source for this black sooty mold fungus on these gardenia leaves. ARS image K9015-1 by Scott Bauer.

Scale insects feed on a wide range of host plants and are common pests of many indoor and outdoor herbaceous ornamental plants as well as many trees and shrubs. Most species are restricted to particular host plants or plant groups, and some are serious crop pests. They feed by sucking plant sap through their long, needle-like mouthparts (six to eight times longer than the insect itself!). Many also excrete sticky honeydew which supports the growth of sooty mold. Sooty mold is a black-colored fungus; when it coats the top side of leaves, that interferes with photosynthesis and makes the plants unattractive and yellow.

There are, however, a few types of scale insects which are economically valuable and are “farmed” for the substances they produce. Cochineal scales (Dactylopius spp.), which grow only on cactus, produce red dyes for coloring foods and dyeing fabrics, several genera of lac scales produce shellac, and there are other species that produce other less common materials. In addition, several species of Dactylopius are used as biological control agents against invasive species of Opuntia cactus.

A cochineal farm on Tenerife, Canary Islands (L), colonies of cochineal scales on a cactus pad (LC), closeup of cochineal scales (C and RC) and desiccated females without the protective white wax (R).

Traditional harvest of cochineal scales on Tenerife, Canary Islands (L and LC), the dried, cleaned insects (C) for sale (RC) and with one added to a glass of water, releasing the red dye (R).

There are two types of scales: the soft scales and the armored scales.

The protective cover of the calico scale (Eulecanium cerasorum), an invasive species, is readily apparent. ARS image K10882-1 by R. Gill.

The soft scales (Family Coccidae) are the more important of the two groups of scales found on indoor plants. Soft scales are round to oval, dome shaped, and 1/8 to 1/4 inch long when mature. Immature scales start out light in color and darken at maturity. Many resemble miniature tortoise shells. Fifty to 2000 eggs or live young, depending on the species, are produced in or beneath the female’s body. The eggs hatch in 1 to 3 weeks. The pale, newly hatched nymphs are the mobile crawler stage, but after finding a suitable part of the plant they settle down for the remainder of their lives. The nymphs go through three instars. A waxy scale covering is produced over the female after she becomes an adult. The waxy scale covering adheres tightly to the body of the female and cannot be separated from it. Female soft scales don’t lose their antennae and legs completely, but are greatly reduced so although they can move, the adults seldom do. They generally overwinter as immature, fertilized females.

Brown soft scale on the underside of cycad leaves.

Soft scales are usually found on the undersides of leaves and stems, although some species may occur on upper leaf surfaces. A heavy infestation will cause yellowed leaves, distorted foliage especially at the growing tips, twig dieback, or defoliation. However, soft scales can be a nuisance long before there are any visible symptoms. Copious amounts of honeydew excreted by the scales will make the plants and everything around or under them sticky and attracts ants, bees, wasps, and flies. A dark fungus called black sooty mold grows on sweet honeydew, blackening anything where the honeydew is deposited.

Some species of soft scales commonly found in the Midwest include:

  • Brown soft scale (Coccus hesperidum) is oval, rather flat, and up to l/8 inch long. It may be mottled shiny pale brown, yellow, or grey with dark brown grid-like mottling. It attacks a wide variety of hosts, and is one of the most common species on houseplants, seeming to prefer perennials over annuals. It is common on gardenia, fern, camellia, oleander, and fig.
  • Female cottony maple scale on maple branch. Photo by USDA Forest Service – Ogden Archives, USDA Forest Service, www.forestryimages.org

    Cottony maple scale (Pulvinaria innumerabilis) is a flattened brown scale about 1/8” long that becomes one of the most conspicuous soft scale insects attacking ornamental plants when mature females begin to secrete white, waxy, cottony-appearing egg sacs in early summer. Severely infested trees look like they are covered with a string of popcorn.

  • European elm scale (Gossyparia spuria) females are a reddish-purple oval surrounded by a white, cottony fringe, while males form visible white cocoons early in spring and turn into reddish adults in mid- to late spring. The eggs are deposited underneath the female’s body and hatch within a few hours into bright yellow crawlers. The crawlers settle along the midrib or along other veins on the underside of leaves where they feed for the summer. They move to a stem or trunk crevice to overwinter, often resembling small mealy bugs since they covered in short, white, waxy filaments. There is one generation per year on all native elms species.
  • Fletcher scale. Image from US National Collection of Scale Insects Photographs , USDA Agricultural Research Service, Bugwood.org

    Fletcher scale (Parthenolecanium fletcheri) is common in the northern parts of the Midwest and Canada and is most frequently found on arborvitae (Thuja sp.) and yew (Taxus sp.). Pachysandra and Eastern red cedar are also susceptible. Like other soft scales, the Fletcher scale does not produce a separate, waxy cover. Instead it secretes a thin, transparent film, which does not totally cover the insect. The amber to reddish-brown nymph overwinters on a branch. The following spring, it feeds heavily as it grows into an adult. At maturity, a single female can produce 500-600 eggs in May, which hatch in late June or early July. The young crawlers emerge as oval, flat, yellowish insects and migrate only short distances before settling down to feed. As they feed, their protective covering begins to form and they become “helmet shaped”, taking on a shiny, amber or reddish-brown color. One generation per year is produced.

  • Various stages of hemispherical scale.

    Hemispherical scale (Saissetia coffeae) is brown, smooth, glossy, and very convex (thus the name), with a slightly flared margin, and about l/8 inch long when mature. It is one of the most common species on houseplants, favoring ferns, asparagus fern, Schefflera, palms, begonia, citrus, chrysanthemum, fig, lily, orchids, and many non-woody evergreen plants. Plants in the family Acanthaceae are especially susceptible.

  • Lecanium scales (Parthenolecanium spp.) includes about twelve species which are difficult to tell apart and resemble deformed plant buds infesting a variety of hardwood shade trees, fruit trees and shrubs. They are brown and dome-shaped or hemispherical and, depending on the species, can be from 1/8 to ½ inch across. Females die after laying their eggs, leaving the dried body to protect the eggs. The crawlers hatch in in late spring or early summer and the immature females return to twigs in late summer where they overwinter. There is one generation per year.
  • Magnolia scale, immature females in August. Image by Missouri Botanical Garden.

    Magnolia scale (Neolecanium cornuparvum), the largest scale found in the US at up to ½ inch in diameter, is a shiny brown, oval dome covered with a white, waxy coating that can be mistaken for plant buds or a fungus on the twigs of magnolias. It overwinters on one-to-two-year-old twigs as tiny, dark-colored crawlers that begin to feed, mature, and change color in the spring. The smaller males turn white and emerge as tiny, pink to yellow gnat-like crawlers. The larger females become brownish-purple, enlarging through early summer. The eggs hatch inside the female so the crawlers are born alive in the fall.

San Jose scale on stem. image from US National Collection of Scale Insects Photographs , USDA Agricultural Research Service, Bugwood.org.

The armored scales (Family Diaspididae) get their name from the hard, waxy covering over the body. Armored scales are generally smaller than soft scales (1/16 to 1/8 inch long) and are not raised and bumpy like soft scales – and therefore are more easily overlooked than soft scales, especially when the scales match the color of the bark of their host tree. The scales vary in shape from circular to elongate (elliptical or oystershell-like) and in texture from smooth to rough, and are variously colored. Underneath a hard cover made of wax and protein is a yellow or orange soft body. Eggs are laid beneath the female’s scale, or in some cases, live young are produced under the scale. The crawlers move to another part of the plant and settle for the remainder of their life. A waxy cover that incorporates the shed skin of the crawler and subsequent stages is produced over the immature insect. Female scales lose their legs and antennae during the first molt. The legless adult female remains under the scale. They usually overwinter as eggs under the hard shell of their mother.

Armored scales are generally found on lower leaf surfaces and stems, often forming thick crusts. Plant injury caused by armored scale feeding is similar to that of soft scales, but tend to have a greater impact on their host than soft scales do. Toxins injected while feeding on leaf tissue kills cells around the feeding site, causing a yellow or brown halo, and heavy feeding can disrupt nutrient flow enough to cause in premature leaf drop or branches to die. No honeydew is produced, however, so sooty mold is not a problem.

White male euonymus scales on pachysandra.

Although common, armored scales are not as much of a problem indoors as soft scales because they are limited in the types of plants they infest (mainly trees and shrubs) and don’t produce honeydew. But outdoors they can be significant problems on ornamental plants. Some species of armored scales common in the Midwest include:

  • Euonymus scale (Unaspis euonymi) is a grey to brown scale usually found on lower branches or on the new leaves of several species of euonymus, bittersweet, and pachysandra. The males produce a small, thin, white covering and can be quite numerous on the undersides of leaves. The females deposit eggs in early spring under the scale covering which hatch into yellow-orange colored crawlers over a two-to-three week period in late May or early June. There are often two generations per year.
  • Oystershell scales crowd together on a twig.

    Oystershell scale (Lepidosaphes ulmi) is a grey or light to dark brown scale shaped like an oystershell with one narrow pointed end. It is found primarily on ash, dogwood, lilac, maple, and willow. The crawlers that hatch in early spring are initially white, but gradually change to a glossy brown. There are two generations per year.

  • Pine needle scale (Chionaspis pinifoia) is a 1/8-inch long white, oystershell-shaped scale can completely cover the needles on many species of conifers. It is probably the most common armored scale found on conifers in the United States and Canada. Their feeing causes plant discoloration, needle yellowing, and even branch death. Eggs hatch in mid-May into tiny, flat, pink crawlers. There are two generations each year.
  • The white, elongated pine needle scales on pine foliage.

    San Jose scale (Quadraspidiotus perniciosus) is the most common armored scale found on deciduous fruit and nut trees, but it attacks many other trees as well as shrubs. This species from China is round and white to gray (becoming darker with age) with a characteristic black raised spot in the center. The crawlers are bright yellow. There can be as many as three generations per year.

Encarsia perniciosi, a parasitoid of California red scale (Aonidiella aurantii) and San Jose scale (Quadraspidiotus perniciosus). Image from INRA-HYPPZ , Institut National de la Recherche Agronomique, Bugwood.org.

Weather and natural enemies, such as lady beetles and parasitic wasps, usually keep scale insects below damaging levels, but if scale numbers become abundant management mat be required. Controlling scales can be a difficult challenge. It’s best to prevent infestations in the first place by carefully inspecting plants before purchasing, but often the scale wax covering blends in with the stem or bark and is difficult to see. Since scales can occur on all plant parts, check every part of the plant.

For lightly infested houseplants, most of the scales can be removed with a soft-bristled toothbrush or cotton swab dipped in either soapy water or 70% isopropyl alcohol. Thoroughly washing the leaves with a mild detergent solution (being careful to avoid wetting the soil) may also work. This will also wash off honeydew and dislodge crawlers. Inspect the plants closely at weekly intervals, and repeat the procedure as necessary (probably several times). If a plant is heavily infested, disposing of it may be the best solution, although that may not be an option for a valuable or cherished plant.

Scales can be managed by mechanical and chemical controls.

Chemical control is often the most effective way to combat scale problems, especially in the landscape. Adult scales, however, are protected from insecticides by their waxy coverings, so chemical control measures should be aimed at unprotected immatures (crawlers). Accurate identification of the scale species is important in order to know when scale crawlers should be active and treatments should be applied. Crawlers may be detected by placing double-sticky tape on plant branches. Spot treatments should be applied when scales are present. Applications of insecticidal soap or horticultural oil will kill scales, but require thorough coverage and usually at least three treatments to control an infestation. Repeat every six to seven days until scales have been eradicated. Synthetic insecticides labeled for scale control may require fewer applications, but some treatments can cause plant damage, so sprays should be tested first on a small part of the plant and all label directions should be followed. Systemic insecticides applied to the soil help suppress populations, but do not eliminate the problem. Applications on larger woody plants can even give unsatisfactory control due to unequal movement of the systemic material in the plant. Horticultural oils, that suffocate the insects, may be effective against some adult scales. Dormant oils need to be applied in early spring before leaves appear to kill the overwintering stage of some species. Dead scales do not fall from plants, so it will be necessary to examine plants to determine whether the scales are dead or alive. When crushed a dead scale will be dry, but if the body is juicy or leaves a streak when smeared on a piece of paper it was alive.

– Susan Mahr, University of Wisconsin – Madison


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Common on backyard trees, ornamental shrubs, greenhouse plants and houseplants, over 1,000 species of scale insects exist in North America. They are such oddly shaped and immobile pests that they often resemble shell-like bumps rather than insects. In many cases, heavy infestations build up unnoticed before plants begin to show damage. Large populations may result in poor growth, reduced vigor and chlorotic (yellowed) leaves. If left unchecked, an infested host may become so weak that it dies.

Identification

Scale insects can be divided into two groups:

Armored (Hard) – Secrete a hard protective covering (1/8 inch long) over themselves, which is not attached to the body. The hard scale lives and feeds under this spherical armor and does not move about the plant. They do not secrete honeydew.

Soft – Secrete a waxy film (up to 1/2 inch long) that is part of the body. In most cases, they are able to move short distances (but rarely do) and produce copious amounts of honeydew. Soft scale vary in shape from flat to almost spherical.

Life Cycle

Adult females lay eggs underneath their protective covering which hatch over a period of one to three weeks. The newly hatched nymphs (called crawlers) migrate out from this covering and move about the plant until a suitable feeding site is found. Young nymphs insert their piercing mouthparts into the plant and begin to feed, gradually developing their own armor as they transform into immobile adults. They do not pupate and may have several overlapping generations per year, especially in greenhouses.

Note: Males of many species develop wings as adults and appear as tiny gnat-like insects. They are rarely seen and do not feed on plants. Females often reproduce without mating.

  1. To get rid of scale insects prune and dispose of infested branches, twigs and leaves.
  2. When scale numbers are low they may be rubbed or picked off of plants by hand.
  3. Dabbing individual pests with an alcohol-soaked cotton swab or neem-based leaf shine will also work when infestations are light.
  4. Commercially available beneficial insects, such as ladybugs and lacewing, are natural predators of the young larval or “crawler” stage.
  5. Organic pesticides, like insecticidal soap and d-Limonene can also be used to kill the larvae. However, these products have very little persistence in the environment, so several applications during egg-hatching will be required for effective control.
  6. Azamax contains azadirachtin, the key insecticidal ingredient found in neem oil. This concentrated spray is approved for organic use and offers multiple modes of action, making it virtually impossible for pest resistance to develop. Best of all, it’s non-toxic to honey bees and many other beneficial insects.
  7. Horticultural oils and other safe, oil-based insecticides work by smothering insects and will control all pest stages, including adults which are protected from most other insecticides by their armor coverings.
  8. Fast-acting botanical insecticides should be used as a last resort. Derived from plants which have insecticidal properties, these natural pesticides have fewer harmful side effects than synthetic chemicals and break down more quickly in the environment.

Tip: Ants feed on the honeydew that sucking insects produce and will protect these pests from their natural enemies. An application of Tanglefoot Pest Barrier to the stalks of woody plants or to the trunks of trees will help get rid of ants naturally.

Scale Insects

Overview of scale insects

Scale insects are sap-feeding insects named for the scale or shell-like waxy covering that conceals their bodies. In Iowa, most species of shade trees, fruit trees, and ornamental shrubs are subject to scale insect attacks. Scale insects can weaken and even kill trees, shrubs and houseplants, but in general, complete loss of the plant is rare.

Description of scale insects


Scales on a ficus. Adult scales are black and to the left;
immature scales are beige and to the right. Actual size 5mm.

Depending on the species, scale insects may be found on plant stems, twigs, trunks, foliage, or fruit.

Most scale insects are small and inconspicuous. The size of scale insects ranges from 1/8 to ½ inch. Color, shape, texture and other features vary with the species.

Scale insects are generally divided into two categories:

• Soft scales produce a soft, thin, cottony, powdery or waxy layer over themselves that cannot be separated from the insect body. These scale insects often produce copious amounts of honeydew.

• Armored scales have a hard, shield-like cover composed of shed skins and wax that conceals the body but is not attached to the body of the insect.

Damage caused by scale insects

Scale insects feed by sucking sap from trees and shrubs through piercing-sucking mouth parts. Sap feeding by scale insects may cause yellowing or wilting of leaves, stunting or unthrifty appearance of the plants, and eventually death of all or part of the plant when infestations are heavy. Weakened plants may lose vigor and become more susceptible to injury caused by drought, severe winters, attack by other insects (such as borers), or infection by diseases.


Sooty mold beneath a tree infested
by magnolia scales soft scales.

While feeding, soft scale insects excrete a sweet, sticky substance called honeydew. Honeydew is a mixture of undigested sugar and water passed through the insect’s digestive system and deposited onto leaves and stems. Honeydew may make the plant appear shiny and wet and also attracts flies, ants, bees, and other insect scavengers. The honeydew may encourage a fungus called sooty mold that gives the plants a characteristic black, “sooty” appearance. Honeydew can foul sidewalk, cars, and houses beneath scale-infested trees.

Life cycle of scale insects

Scale insects have a simple life. Eggs are laid underneath the scale covering of the adult female. When the eggs hatch, tiny immatures, known as


Eggs underneath a female scale.

nymphs, emerge. Nymphs have legs and antennae and are called “crawlers” because they walk away from the maternal scale to settle at new feeding sites. For most common scales, this is the only stage that crawls about on the plant. When the crawlers arrive at a suitable location, they insert their mouthparts into the plant, and begin to feed on the plant’s sap. The shell or scale characteristic of the species develops soon after feeding begins. The legs and antennae of most species are lost as the nymphs grow.

Nymphs and adult females for most species remain at the same location for the rest of their lives. Adult males are tiny, flying, gnat-like insects that fly to new females for mating. Scales may go through one or more generations each year.


Small holes in the scales indicate that a parasitic
wasp emerged from them.

Pest management of scale insects

Scale insects are difficult to control because the waxy or cottony covering serves as a protective barrier to traditional contact insecticides. However, a pest management program that incorporates natural, mechanical, and/or chemical controls (as described below) should provide satisfactory control of most scales on most ornamental plants.

Natural control of scale insects

Parasitoids (small parasitic wasps) and predators (such as lady beetles) can attack and significantly reduce scale insect populations. Other natural mortality factors (such as adverse weather) may influence populations, causing year-to-year variations. The presence of biological and natural controls can keep scale populations low, so insecticide treatments are not needed. Observe closely the progress of scale infestations. If scale numbers decrease (or continue at a low level), do not treat. Rapidly increasing scale populations and/ or heavy infestations should be treated as outlined below. Plants produced for sale must be treated so they remain pest free.

Mechanical control of scale insects

Mechanically removing scale insects may be practical in certain situations such as small infestations on houseplants or on small trees and shrubs. Heavily infested stems can be pruned out and discarded to reduce scale populations.

Chemical Control of scale insects

Insecticide applications may be warranted when natural enemies and mechanical controls are not sufficient to prevent plant injury. There are three chemical control strategies for treating infested trees and shrubs: spray dormant oil prior to bud break, apply a contact insecticide in summer when the crawlers are active, or use a systemic insecticide.

Dormant Oil: A thorough application of horticultural oil according to label instructions just prior to bud break in late March or early April (while the plant is dormant) may control scale insects on trees and shrubs. Effective control requires a thorough treatment of all aboveground plant parts.

Summer Sprays: Contact insecticide sprays do not penetrate the protective covering of the most scales. Therefore insecticide treatments are most effective when applied during crawler emergence, immediately after egg hatch. There are four methods for determining when eggs are hatching and when crawlers will be vulnerable:

1. “Calendar Approach:” Spray at the “average” time eggs have hatched in your area in the past, according to published literature. These approximate dates are not always accurate because of year-to-year weather fluctuations.

2. “Pest Development:” the life cycle stages of the insect, such as egg hatch can be estimated for some species by adjusting the average expected timing for current weather conditions.

3. “Plant Development:” Year to year weather variation in weather and insect development can be estimated by the use of phenology (the known influences of weather variations on plant and animal rhythms). By watching known phenological indicator plants you can accurately predict when a particular scale’s eggs hatch will hatch in your area. Note that the indicator plants are not infested with the scale in question.

4. Visual Inspection:” Carefully examine the infested plant to see if crawlers are present or shake a branch of the infested plant above a sheet of white paper and examine the paper for crawlers. Alternatively, place double-sided tape around the twigs or branches in affected areas of the plant when crawlers are expected. The tiny insect’s bodies get stuck in the adhesive. A magnifying glass can help with identification.


Magnolia scales are large and
easy to see. Many types of scales
are hard to see.

Most home lawn and garden insecticides found in garden stores (including insecticidal soap and horticultural oil) are appropriate for use on ornamental trees and shrubs in Iowa. Check the pesticide label of each product to make sure that the type of scale and the name of the host plant are listed for that product. Always read and follow label instructions on mixing, usage and application safety.

Old scales may remain harmlessly on the plant for some time after the death of the insect. To evaluate the effectiveness of treatments, slide your thumb across a group of scales. If scales are dead, they will be hollow and the coverings will flake off easily. Living scales will leave a colored, wet residue on your thumbnail.

Systemic insecticides are injected into the plant or are applied as a foliar spray, drench or soil injection under an infested tree or shrub. Systemic insecticides circulate through the plant and can control both crawlers and adult scales with less impact on natural enemies and less risk of pesticide drift. However, systemic insecticides can be time consuming and expensive and they may be effective only on those scales infesting the leaves or those that are actively producing honeydew.

Other resources

Scale Insects on Ornamental Plants

Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them. Please see our website for current forms, fees, and instructions on preserving and mailing insects.

Contact information for each states diagnostic laboratory for U.S. residents. If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.

Scale Insects – Houseplants


Fern infested with scale

  • Soft scales are sucking insects that attack a wide variety of plants. Heavy infestations may cause leaf yellowing, stunting, and dieback.
  • Soft scales such as brown soft scale and the hemispherical scale are common pests of houseplants.
  • They appear as raised bumps on leaves and stems, vary in color and can be scraped off.
  • They produce honeydew and sooty mold may be present on leaves below infested branches.
  • Armored scales are not common on houseplants, but may be a problem on some orchids.
  • They are flattened, small and do not produce honeydew.
  • They are difficult to control on orchids, because they may be protected under the sheaths. Careful examination of the plants is essential to control. The scale bodies may be scraped off and treated as for other scale on houseplants.
  • Examine the scale for parasite activity, especially if the plant has been outdoors. Parasitized scales will appear dark in comparison to normal scale insects.

Management

  • Infested plants should be quarantined.
  • Heavily infested plants should be discarded.
  • Wash off or crush any visible scale insects. Often they are found on the stems, underside of leaves, or along the leaf mid-veins.
  • Treat with an insecticidal soap or horticultural oil labeled for houseplants or a houseplant spray that is registered for use.
  • There are also systemic houseplant insecticides that are labeled to be used in the soil to help control scale.
  • Be sure the plant and insect are on the label and follow all directions carefully.
  • Some houseplants are sensitive to chemical sprays, especially soap.
  • Multiple treatments are necessary.
  • Outdoors scale is kept under control by beneficial insects. Spray your houseplants with insecticidal soap or oil before bringing them back indoors in the fall.


Philaphedra scale on croton


Brown soft scale and honeydew


Armored scale on houseplant


Armored scale on orchid

Close-up of armored scale on orchid

Close-up of brown soft scale

Hemispherical scale on spider plant

By Mark A. Muegge and Michael Merchant

Many species of scale insects damage landscape plants, shrubs and trees. Scale insects insert their mouthparts into plant tissues and suck out the sap. When many of these insects attack a plant, its growth may be stunted; its leaves may develop yellow blotches; the branches may die; and some or all of the leaves may fall off.

Although scale insects are common, they are probably the most misidentified of all insect groups. Scale insects are generally small (1/4 inch long or less) and often mimic various plant parts, such as bark and buds. Other species appear as small, white, waxy blotches or small bits of cotton on leaves and stems. The one attribute of scale insects that probably leads to most misidentification is that they appear to be nonliving: Once the young settle on a plant, they generally don’t move and are often overlooked.

To control scale insects most effectively, you need to know how to identify them, when in their life cycle to treat them, and what methods and chemicals work best for the various species. It’s also good to be able to recognize their natural enemies, so you can use them to help you combat scale insects.

Knowing this can help you:

  • Time your pesticide applications to control the most scale insects;
  • Avoid wasting time and money applying chemicals that don’t work at certain stages of the insect’s life cycle; and
  • Release fewer unnecessary chemicals into the environment.

The life cycles of scale insects vary considerably among species. Their life span may last from a few weeks to several months. The various species can have from one to several overlapping generations every summer. Females can give birth to live young or lay eggs.

Depending on the species, scale insects can spend the winter (overwinter) as eggs, young or adults.Under greenhouse conditions, they may not overwinter at all.

However, all scales have two life stages in common: a mobile stage, generally followed by a motion- less development period.

The mobile stage is the first developmental stage, in which the nymphs move about. At this stage they are called “crawlers.” Scale crawlers generally emerge in spring or early summer and at the beginning of each generation. This is the stage at which scale insects can be controlled most effectively.

Crawlers search for a suitable location on the plant on which to settle and feed. Once they settle, scale insects enter the motionless development period. Most species never move again in their lives.

Scale insects feed by inserting their hairlike mouth- parts into plant tissue and siphoning the plant’s sap. While feeding, many species excrete a sweet, sticky liquid referred to as “honeydew.” If many of them infest a plant, the honeydew can accumulate on the stems and leaves, making them appear shiny.

In humid areas, a fungus can grow on the honey- dew. Because this fungus makes the plant leaves and stems appear sooty, its common name is “sooty mold” (Fig. 1).

Honeydew also attracts ants, and some ant species actually “tend” scale insects for honeydew, while giving protection from predators and parasitoids (small wasps that lay eggs in hosts). Under these conditions, scale insect populations can skyrocket. As scale insects grow, many species exude wax from pores on their bodies. This wax generally forms a protective covering that may or may not be attached their body. Scale insects with hardened wax coverings that detach easily from their soft bodies underneath are referred to as “hard” or “armored” scales (Fig. 2).

Two other groups of scales produce waxy coverings that are attached to their bodies:

  • Soft scales, which are mottled light to dark brown; adults generally do not move.
  • Mealy bugs, which are covered with soft, white wax that can be rubbed off easily (Fig. 3-4). All developmental stages of mealy bugs have legs and can crawl, but they move slowly and infrequently.

Some of the more common plant infesting scale insects and plant symptoms are shown in Table 1.

Sampling for scale crawlers

Because of their protective wax covering, most scale insects are very difficult to control with insecticides once they have settled. Scale insects are most vulnerable to spray formulations of contact insecticides during the crawler stage of development.

Generally, the crawler stage lasts from 2 to 4 weeks; however, scales that have multiple generations per year may have crawlers present at all times. To detect this stage of development, you need to inspect scale-infested plants often.

Scale crawlers are tiny (1/16 inch long or smaller), making them difficult to see. To see if scale crawlers are on a plant, use either of these two simple detection methods:

Method 1: In early spring before new plant growth occurs, wrap a small piece of double-sided sticky tape to a stem above a scale infestation (Fig. 5).Crawlers that are moving to new locations will become caught on the tape. Crawlers move toward light. Placing the tape above the scale infestation will increase your chances of finding the crawlers if they are present.

If crawlers are on the plant, the tape will become covered with tiny, cream to light-yellow specks. A magnifying glass can help you verify that crawlers are present.

Method 2: Gently tap a scale-infested stem or leaf over a sheet of white paper. If scale crawlers are present, they will fall onto the paper, where you can easily see them moving about.

Using natural enemies to control scales

Many natural enemies—small parasitic wasps, lady- bird beetles and some fungi—can significantly reduce scale insect populations. Before using pesticides,check for natural enemies. Ladybird beetles (commonly known as ladybugs) are easy to spot, but parasitic wasps are more difficult to see because they are so small.

Parasitic wasps often emerge from scales by chewing small, round holes in them. Examine several scales to see if they have these exit holes (Fig. 6). Also, check to see if ants are tending the scales; if so, natural enemies may be ineffective.

If natural enemies are present and it appears that there are few scale insects or that no ants are attending them, wait a few days and check again. If natural enemies are controlling the scale infestations, you do not need to use pesticides.

Some natural enemies are available for managers of interiorscapes and greenhouses to buy to control scale insects and mealybugs. These specific parasites are species of Leptomastix, Pseudaphycus, Rhyzobius and Aphytis. A small beetle called the mealybug destroyer (Crytolaemus) also is available. For a list of commercial suppliers, contact the Department of Pesticide Regulation, California Environmental Protection Agency,1020 North Street, Room 161, Sacramento, CA 95814-5604 or on the Web at www.cdpr.ca.gov.

Use pesticides on landscape plants only if the scales are injuring the plants significantly. Always consider removing, destroying and replacing heavily infested ornamental shrubs and trees . Insecticides labeled for control of scale insects may harm beneficial insects.

Pesticides for scale control

Many pesticides are available to consumers wanting to control scale insects (Table 2). These can be divided into three general groups based on how they control scales: Some poison the insects; others suffocate them or cause them to dry out and die; and still others, calle d insect growth regulators or “IGRs,” disrupt molting.

Poisons : The most common group of poisons is the nerve poisons. These insecticides disrupt an insect’s nervous system. They are absorbed through the insect’s exoskeleton “skin” and are considered “contact insecticides.” Common contact insecticides include carbaryl, diazinon, chlorpyrofos, pyrethrins, and permethrin.

Other poisons have “systemic” activity, meaning that when they are applied to the plant’s leaves or roots, the plant absorbs the insecticide into its tissue, and the scale insect is poisoned when it feeds from the plant. Examples of systemic insecticides are imidacloprid, dimethoate and disulfoton.

Some products, such as acephate and dimethoate, are both contact and systemic insecticides.

Suffocating / drying pesticides: Scale insects are suffocated by oils and dried out by insecticidal soaps.

Consumers may buy two kinds of oils for treating scale insects: dormant oils; and summer horticultural or parafinnic oils. Both types affect immature and adult scale insects. Dormant oils may be applied only to deciduous plants (trees and shrubs that lose their leaves in the fall) when the plants are dormant. Be careful with evergreen plants: These oils may injure or discolor some species.

Summer oils are lighter than dormant oils and may be applied during the summer on deciduous plants and throughout the year on many evergreen trees and shrubs. Some horticultural oils may also be mixed with other insecticides to control scale insects more effectively.

Insecticidal soaps disrupt the waxy cuticle or “skin” of the insect, which eventually causes the insect to dry out (desiccate ) and die.

IGRs: Insect growth regulators interfere with an immature scale insect’s ability to molt (shed its outer skin to allow for growth); in some cases, IGRs suppress egg development. Although these insecticides often act more slowly than contact insecticides, they can effectively control many species of scales.

Examples of IGRs include azadirachtin and pyriproxyfen.

Most insecticides are formulated as:

  • Wettable or soluble powders (WP, S), which are mixed with water and sprayed onto an infested plant;
  • Emulsifiable concentrates (EC), which also are mixed with water and sprayed onto infested plants;
  • Granulars (G), which generally are applied around the base of a plant and watered into the soil;
  • Dusts, which are applied directly onto infested plants;
  • Aerosols, which also are applied directly onto plants.

Beware of phytotoxicity, which is the damage that pesticides cause to plants. Many plants are sensitive to various pesticides. If you’re in doubt, treat a small part of the plant, then check a day or two later to see if the plant tissue is yellowed or burned . Many pesticide labels list the plants that are susceptible to phytotoxicity if those products are used on them.

Pesticide application to control scales

Pesticides work best on scale crawlers. Because crawlers can take from 2 to 4 weeks to emerge completely, check the scale-infested plant at least weekly until you see them. For effective control, you may need to apply pesticides two to four times at 5- to 7- day intervals, because most pesticides work for less than a week, but crawlers from a single generation can hatch over several weeks.

Regardless of the number of applications needed , you must cover the plant thoroughly with insecticide each time, particularly when you’re using contact insecticides. Cover both sides of the leaves and all the twigs and branches.

Dormant oils should be applied before spring growth begins, when temperatures are above 45 degrees F for 24 to 48 hours. Follow the instructions on the product label on how to dilute and apply the pesticide.

Apply summer sprays when temperatures are below 90 degrees for 24 to 48 hours. Spray two to four times at 7- to 10-day intervals when the crawlers are active. Emulsifiable concentrate (EC) sprays are preferred . Summer oils can be used alone or in combination with other insecticides.

When scales are on plants that are actively growing, apply systemic insecticides such as imidacloprid around the base of scale-infested trees , shrubs or potted plants. Follow the instructions on the product label on dilution and application rates.

To control scales infesting houseplants, you can use a commercially available insecticidal soap or make your own soap solution by diluting a mild dishwashing detergent. If possible, dip the entire plant into the soap solution, otherwise thoroughly cover all plant part s using a hand-held sprayer.

You may need to reapply the soap to control the scales effectively. You may also use systemic insecticides by applying the appropriate solution around the base of the plant. Check the product label for application and dilution rates.

To remove minor scale infestations on small house- plants, use cotton balls or swabs to brush rubbing alcohol onto the plant.

Contact insecticides, such as aerosol sprays containing pyrethrins and permethrin, may also be used on houseplants, but they don’t work for long. Reapply them at 1- to 3-day intervals until the scales are controlled. Spray any aerosol from at least 12 inches from the plant.

Evaluate the effectiveness of treatments to determine if you need to make further applications. To see if you’ve controlled the scales successfully, slide your thumb across a group of scales. If scales are dead,they will be dry and hollow and will flake off easily.

Policy statement for chemical control suggestions

Regulations on insecticides change frequently, and changes may have occurred since this publication was printed. The pesticide user is always responsible for the pesticide residue s’ effects on plants or household goods, as well as for problems that arise when neighboring property or plants are contaminated . Always read and follow carefully the instructions on the container label.

Download a printer-friendly version of this publication: Scale Insects on Ornamental Plants (pdf)

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Scale insects can infest and damage many of the plants we grow in our landscapes and indoors. They feed on the sap of plants, and a large enough population can weaken a plant, damage it or even kill it.

View full sizeTony O. Champagne / The Times-Picayune

Scale can be difficult to detect. Once the insects settle down to feed and pierce the plant’s tissue with their needle-like mouth parts, they never move again and become firmly attached to the leaves or stems. Scale insects also cover themselves with waxy material that protects and hides the insect.

These two characteristics make scale look like anything but a bug, and many gardeners don’t recognize that there is a problem until a plant is heavily infested and damage has occurred. Many people misdiagnose scales that cover themselves with white fuzzy material as a fungus attack.

Types of scale

There are many types of scale, but here are a few of the most common ones.

  • Tea scale insects appear as a slightly fuzzy white and brown coating on the underside of the leaves. They are the primary insect pest of camellias and can also infest some hollies (notably Burford hollies).

What to look for

As scale insects feed on the sap of a plant, they excrete tiny droplets of a sugary liquid called honeydew. The droplets of honeydew fall and accumulate on foliage below, which can cause that foliage to look shiny and feel sticky. (It can also make objects under the infested plant shiny and sticky).

This rich food source does not go unnoticed. Ants, wasps and other insects may be attracted to the sweet honeydew.

Even more common is the growth of fungal organisms that produce a black coating on the leaves called sooty mold. These fungi feed on the honeydew and do not attack or directly damage the plant. Sooty mold, however, has an unattractive appearance and is often the gardener’s first noticeable sign of trouble.

Do be aware that other sucking insects, such as whitefly and aphids, also produce honeydew that can lead to sooty mold. And, sooty mold does not occur with all types of scale: Neither tea scale nor fern scale cause sooty mold.

Scales spread from plant to plant as newly hatched crawlers, which are very tiny, have legs and can move around. Crawlers are fairly easily controlled with commonly available contact insecticides. Unfortunately, scale crawlers are hard to detect. Most gardeners never notice them and miss the opportunity for control.

Many scales produce crawlers in the spring. Once the crawlers have settled down to feed, they create their protective covering and contact insecticides are largely ineffective.

Controlling scale

Scales are generally not one of those insect pests that will just go away eventually if you leave them alone. Control is almost always necessary.

The least-toxic, effective insecticides to control scale are oil sprays. These insecticides contain oil in a form that will mix with water. When mixed and sprayed onto an infested plant, the oil coats the scale insects and clogs their breathing pores. The insects are suffocated rather than being killed by a toxic material.

Brand names include heavier oils like Volck Oil Spray and light oils like Year Round Spray Oil, All Seasons Oil Spray and others. I like the light horticultural oils, as they can be used all summer.

For proper control, it is critical to apply the oil spray over every surface of the plant. If the insects are on the underside of the leaves and the oil is only applied to the upper surface, it will have no effect on them. Because scales are difficult to eradicate, a second, and even a third, application should be made following label directions.

Oils are also effective against aphids, whiteflies, spider mites and the crawler stage of scales. In addition to their low toxicity, oil sprays do not leave behind a residue that may be harmful to beneficial insects.

An added benefit of oil sprays is that they also help clean the unsightly sooty mold from the plant.

Once a heavy layer of sooty mold forms, it will not quickly disappear, even once the scale has been controlled. This is a good reason not to wait until there is a lot of sooty mold before you control the scale. But as the food supply is exhausted — that is, once the scale insects are dead, no more honeydew is excreted — the sooty mold will eventually weather off. Oil sprays can help speed the process along.

Systemic insecticides are another option for controlling scale.

These insecticides are sprayed onto the plant or applied to its roots. The plant absorbs the insecticide into its tissue, and it gets into the plant’s circulatory system and, eventually, into the sap. When the scale insects feed on the sap, they ingest the toxic insecticide and are killed.

Acephate (various brands) and imidacloprid (Bayer Advanced Tree and Shrub Insect Control and other brands) are systemic insecticides that are effective against scale. Systemic insecticides provide an option for control when temperatures limit the use of an oil spray, or, in the case of soil-applied products, when spraying the plant is not practical (such as treating a large tree).

Always read and follow label directions carefully when using any pesticide.

Now is a good time to check your plants carefully for signs of scale. With luck, you won’t find any, but if you do, now you know what steps to take to deal with the situation.

DAN GILL’S MAILBOX

View full sizeSusan Poag / The Times-Picayune archiveShrubs such as the rose of Sharon or althea (Hibiscus syriacus) have a natural life expectancy of 20 to 30 years.

I have a rose of Sharon that was 40 to 50 years old and about 15 to 17 feet tall. Late last summer it toppled over, and I was wondering if you would know what might have caused this to happen.

Jamie

Age was certainly a factor in the loss of your rose of Sharon or althea (Hibiscus syriacus). We grow plants in our landscapes that live anywhere from a few months (annuals) to centuries (live oaks). But, it is important to remember that, like other living organisms, all plants also grow old and eventually die. In general, many shrubs are considered old when they reach about 20 to 30 years, making your rose of Sharon venerable indeed. When they grow old, plants lose vigor and become more susceptible to health problems. Since your rose of Sharon fell over, the indication is that the root system was attacked and damaged by fungus organisms living in the soil. At some point, the decaying root system could no longer support the weight of the plant, and it toppled over. The direct cause of death of your rose of Sharon was root rot, but age was definitely the underlying factor.

********

I have a monkey grass problem. It is choking up all my beds. I have been digging for a week and have hardly scratched the surface. I’m afraid to use a herbicide because of the close proximity to plants that I want to keep. Any suggestions?

Jason Harris

When a problem is left for a long time to develop, the solution will not be quick or easy. Monkey grass generally should not be used to edge beds because of its tendency to spread back into the bed. If this is not noticed and occurs over many years, the problem can be daunting when finally tackled. Since desirable plants are close at hand, you will need to be very careful about using herbicides. Monkey grass is somewhat resistant to glyphosate (Roundup and other brands), so using this herbicide will not necessarily do a great job of killing it. Still, you can try glyphosate mixed at the strongest rate and apply it just to the foliage of the monkey grass while keeping it away from desirable plants (shield plants or cover them with plastic bags when you are spraying). Only spray enough to wet the foliage of the monkey grass. Although the job is a huge one, regular efforts to physically dig out the monkey grass over time will eventually do the trick. This will only work if you are willing and able to take a section of a bed at a time and clean it out and continue to do this regularly through the coming year. Given your current situation, you may decide to remove the monkey grass edging when you clean out a bed. An alternative would be to leave an edge of monkey grass as thick as you like, and then install bed edging material (available at nursery and building supply stores) behind the monkey grass to prevent it from running back into the bed.

********

I am interested in composting. I have looked on the Internet and seen what seems like a zillion different compost bins. I was wondering if you have any suggestions on what to look for, or even the name of a specific one. I want to stay away from the open bins, since I’m sure my neighbors wouldn’t appreciate the smell. Other than that, I’m open to suggestion.

Jane Boulin

Properly maintained compost piles do not smell. Indeed, odor is only very rarely a problem under rather unusual circumstances. All a compost bin does is to contain the organic matter neatly in some specific area; really, that is its basic function. Some types are designed to spin or turn, which helps make aerifying the pile easier. These types of bins, however, are only suitable for situations where relatively small amounts of organic matter are being produced, since most types don’t hold a lot of organic matter. Do look at the size of the bins you are considering in relation to the amount of organic matter your landscape produces: Many smaller size bins can be overwhelmed by lots of leaves from shade trees and grass clippings from large lawn areas. A basic and functional bin can be made by bending 15 feet of hardware cloth or wire mesh fencing material into a circle and fastening it with wire. It’s inexpensive and works fine.

********

Dan Gill is extension horticulturist with the LSU Ag Center.

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Dan Gill, garden columnist

The Times-Picayune Living Section

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Scale are typically immobile pests that suck plant juices, taking vital sugars away from the plant. They are sometimes hard to identify and often mistaken for natural deformities on plants like galls. Scale have waxy coverings that protect them from most insecticides, so it is ideal to treat them while they are in the larvae, or crawler stage.

Scale insects can be serious pests on trees, shrubs, and other perennials. Most people don’t recognize them as an insect because most immatures (nymphs) are immobile, wingless, and lack a separate head or other recognizable body parts.

Scale insects can be broken into two general categories: soft and armored (hard). Soft scales secrete a soft, waxy layer over them that cannot be detached from their body. They often move between branches and leaves during their lifetime, and secrete honeydew. Armored scale form hard, shell-like covers that can be removed from their body. They typically do not move to leaves, and do not produce honeydew. The scales in this stage are all immobile females.

Immature scale are soft bodied, mobile, and called crawlers. They search for a suitable feeding site, and then secrete a protective shell. They are active in the crawler stage.

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