Citrus scale is a common pest in gardens, orchards, and homesteads where citruses are grown. This pest causes a massive amount of damage to citrus on a global scale.
The insects reproduce quickly and can rapidly drain a tree to the point where it might even die. Even if they don’t kill the tree, they interrupt fruit production and can open the tree up to other pests and diseases.
Read on to find out how to prevent, treat, and manage these obnoxious critters.
What We’ll Discuss
What is Citrus Scale?
Citrus scale are part of the massive phylum of insects known as arthropods (Arthropoda), which accounts for about one million species on planet Earth. The majority are insects, but the arthropod world also includes crustaceans such as lobsters and crabs.
Arthropods can be adapted to both land and water environments. What groups them together are their harder outer layer (exoskeleton) and softer insides, which are connected together.
All of these pests belong to the suborder Sternorrhyncha.
Citrus scale kind of look like a mixture of some ancient sea creature and a land insect. They are usually somewhat flat and oval and can have a hard or soft shell that protects them. They use their needle-like sucking mouthparts to draw out the sap from inside the plants.
Those long, straw-like mouthparts reach the living tissue (the phloem) of the citrus tree or plant. They then suck out the sap, depriving the plant of the nutrients it needs to survive.
Lifecycle
Citrus scale are unique in the way they develop and multiply.
Female scale lay tiny, oval-shaped eggs on leaves, twigs, or branches of host trees. These eggs are protected by a wax coating.
As the eggs hatch, they release tiny, mobile nymphs that begin to feed on the plant’s sap. These nymphs are called crawlers. As they age, the nymphs become immobile juvenile adults with a wax covering or exoskeleton.
Males usually live for a matter of hours and do not have mouth parts. At maturity, males have some leg formation, but it is their wings that enable them to become mobile enough to mate.
Once the females insert their mouth parts into the citrus tree or plant, they stay there. They don’t move from that spot, eating and reproducing in place. Depending on the species, they can reproduce sexually or asexually, producing eggs without a male.
Scale insects secrete a residue known as honeydew. This sticky wax can coat the plant and might attract sooty mold. Infestations are often first detected by the presence of this dark black mold or the sticky honeydew rather than seeing the pests themselves.
Relationship with Ants
Where scale go, so do ants. Ants support the accumulation and reproduction of citrus scales. They have a unique relationship where the ants farm the scale, assisting them to spread quickly and effectively.
Ants are particularly drawn to the honeydew sap that scales secrete. The dew is a huge food resource for the ants and young.
Often, when citrus trees are in pots around the garden or on the patio, ants build nests in the pots close to your scale problem. Like an ant grocery store, they want to be close to their food source. In turn, the ants protect the scale by attacking predators.
Habitat
It’s worth understanding the preferred habitat that lets this pest thrive. They like warm and dry conditions, typically between 70°F to 85°F. These temperatures are ideal for scale development and reproduction.
They are primarily found on the stems, twigs, and sometimes leaves or fruit. They prefer to attach and feed on the more rigid parts of citrus trees.
However, citrus scales can easily survive various environments and are adaptable. This is particularly true if you have your citrus trees in a sheltered spot, so colder regions aren’t free from the risk.
These pests come in two main groups: armored scales and soft scales. This grouping is based upon the outer shell of the of scale species. Let’s look at armored, first.
Citrus Scale Species
Armored scales form a hard outer shell during their developmental stages to maturity. Their outer layer is created through wax excretion and old skins from molting, which bind to their new form and harden, forming a protective armor.
Soft scale insects are smaller and have softer bodies than armored scale insects. Their shells are coated in protective wax. However, because of the soft shell, their bodies are easier to puncture.
Soft scale insects can secrete more honeydew than armored scale. They are more attractive to ants, too.
Black Parlatoria
Black parlatoria (Parlatoria ziziphi) in an armored citrus scale that targets a range of fruit trees, not just citrus.
They are typically black or dark brown in color they can be found on the underside of leaves or on the branches of the host plant.
Caribbean Black Scale
These soft scale insects are sometimes incorrectly called Caribbean black aphids (CBA), but Caribbean black scale (Saissetia neglecta) is not an aphid. It closely resembles one in terms of size and shape, however.
They are black or dark brown in color and small oval shaped.
They like all parts of many species, but citrus is their preferred residence. They attach themselves to leaves, stems, branches, trunks, and fruit.
Citricola Scale
Soft citricola scale (Coccus pseudomagnoliarum) are brown, gray, or somewhat translucent. They generally stick to the upper leaf surface and twigs, though they can sometimes be found on the fruits.
While they can be a problem in Florida and California, they are less common than red or cottony cushion scale.
Citrus Snow Scale
Citrus snow scale (Unaspis citri) are one of the more common forms of armored scale insect that infests citrus trees. These pests have a white powdery covering that gives them a snowy appearance, hence the name.
Cottony Cushion Scale
Cottony cushion or cottony camellia scale (Icerya purchasi) feed on citrus and other plants such as camellias and ornamental shrubs.
The females are red, orange, yellow, or brown, and are partially or fully covered in a white or yellow wax. Males are rare and females are hermaphrodites. They produce a cottony white egg sac.
When targeting citrus, this soft scale doesn’t hold back and will multiply rapidly on all areas of the plant. They can be extremely devastating to a young tree.
It has a natural predator, the vedalia beetle (Rodolia cardinalis). The introduction of this predator in the late 19th century played a crucial role in managing cottony cushion scale infestations on citrus trees in California.
Florida Red Scale
Florida red scale (Chrysomphalus aonidum) likes ornamental plants and a range of citrus.
They are named for the reddish-brown coloring of their armored shell. They attach to the wooded parts of the tree and foliage, as well as fruit surfaces.
They will literally suck the entire plant dry in large numbers.
Purple Scale
Purple or mussel scale (Lepidosaphes beckii) will infest a range of species, such as hibiscus, but citrus is a favorite.
The shape and color of the armored shell distinctly resemble a mussel, the bivalve mollusk found in both fresh and seawater.
Purple scales attach themselves to stems and the underside of leaves. Because they are tiny, a magnifying glass can help identify them.
Red Scale
Aonidiella aurantii, commonly known as red scale, is a massive problem in Florida, California, parts of South and Central America, the Mediterranean, and South Africa.
The female is reddish-brown and oval, and hangs out in the depressions on citrus trees. In addition to feeding on the tree, this armored scale injects a toxic saliva that further harms the tree.
Signs and Symptoms
Any type of scale will reproduce rapidly to damaging levels if left unchecked, so keep an eye out for symptoms.
The most common symptom is yellowing or mottling of leaves. You might also see sooty mold, a black substance on leaves, stems, and branches. It might completely coat the plant parts or appear in spots and blotches.
You might also notice a sticky residue when you touch the plant. This is the honeydew excreted by the citrus scale.
If you look closely, you might notice the presence of scale bodies. They appear like little bumps.
If you notice lots of ants over the citrus plant, that’s a sign to look more closely since they tend to go hand-in-hand.
More vaguely, the plant might lack vigor, and the fruit development will be poor, misshapen, discolored, or absent. You might also see premature fruit dropping. Blemishes on the fruit and damage to the surface might be visible, as well.
Prevention and Management
With citrus scale, there are some key steps you can take to make your trees or plants less enticing. We’ve devised four key steps we like to call PPOT (Prevention, Predators, Observe, and Treat) to help you.
Prevention
Keeping your citrus trees healthy and well cared for is vital to preventing the onslaught of scale insects. Weakened or stressed plants become easy prey for these sucking pests.
Maintain good garden hygiene, feed your plants on a regular schedule, and remove debris and weeds regularly. Sick plants should be carefully monitored for the first sign of citrus scale.
Make sure there is airflow between the trees and, if in pots, they are in locations that allow free drainage and airflow. The pots should be off the ground to avoid ant nesting.
If you purchase any new shrubs that can act as hosts, like camellias or hibiscus, or are adding new citrus trees, isolate and check the new plants prior to purchase. Try to buy from reputable sources.
Predators
Introducing or attracting natural predatory insects of citrus scale is a huge step in their control and should be your second line of defense after keeping plants healthy. There are many predators that will keep populations under control, including:
- Ladybugs or ladybeetles (Family Coccinellidae)
- Lacewings (Family Chrysopidae)
- Predatory mites (Phytoseiulus, Galendromus, Neoseiulus spp.)
- Parasitic wasps (Aphytis spp., Coccophagus, Scutellista cyanea, Metaphycus luteolus, M. stanleyi, M. nietneri, and M. helvolus)
- Vedalia Beetle (Rodolia cardinalis)
These natural enemies can help keep scale populations in check and reduce the need for more intense options.
Healthy gardens will have large populations of predatory insects, so create a healthy environment by having lots of different species, avoiding the use of pesticides, avoiding overcrowding, and addressing any problems right away.
You can also encourage biodiversity in your garden by planting various species that support these predatory insects, such as:
- Alyssum (Lobularia maritima)
- Yarrow (Achillea millefolium)
- Dill (Anethum graveolens)
- Fennel (Foeniculum vulgare)
- Coreopsis (Coreopsis spp.)
Observe
It is vital to maintain a watchful eye on your garden. Regularly check the trees for any signs of problems. Early detection of scale means prompt action can be taken.
Watch for busy ants from roots up the trunks and follow them. If scale is there, the ants will lead you straight to their location.
Rub your finger up the trunk or along the branches and leaves if you can’t spot them. Feel for any sticky residue. If need be, inspect any bumps with a magnifying glass.
Treat
If you suspect or have confirmed citrus scale is the problem, then there are ways to reduce their grip and to prevent them from literally sucking the life out of your plants.
To control the problem, you’ll need to use multiple methods of attack. First, make sure your tree has adequate water and food. It’ll need support to rebuild its health. At the same time, don’t overfeed, as this can stress trees.
Don’t forget to encourage or purchase predatory insects!
Prune out any heavily infested leaves, limbs, fruits, or branches and burn or dispose of them in a sealed container. Then, scrape off any other pests you see using a butterknife or something similar. Drop them in soapy water to drown them.
You can also use chemicals to control citrus scale, but be aware that many populations have become resistant to organophosphate.
A better option is to rotate organic methods. Use any of the following, but instead of sticking to the same treatment week after week, rotate two or three options.
