Scale insects are small pests that get their name from their resemblance to a small circular fish scale. As adults, they are immobile, attaching themselves to leaves and stems and growing a hard or waxy protective outer shell.
Scales have short life cycles and can reproduce multiple times in a single growing season. Scale bugs infect plants when they are young by hopping, walking, or being carried by the wind to new plants. They tend to target sick or otherwise weakened plants, or they may ride on a nursery plant.
There are many other reasons why scales might be infesting your plants, and any of them can pose a real threat to your garden or house plant collection. Read on to learn about six reasons why you might have scale bugs on your plants and some tips and tricks for getting rid of them.
- Scale are small insects that attach themselves to plants and resemble fish scales.
- Once in their adult stage, scale are immobile. Young scale are able to move and infect other plants
- There are various ways to remove scale from plants, including sprays, physically removing, and using natural predators.
Scale Insects Come In Two Varieties
To correctly identify scale, you should know that there are two types of scale with slightly different characteristics. Both soft and armored scales produce a protective outer shell-like covering, and this shell is where the main difference lies.
Below is a summary of the main differences between armored scale and soft scale:
|Hard, protective cover made of waxy secretions
|Soft, protective cover made of powdery wax or filaments
|Smaller in size
|Larger in size
|Attachment to Plant
|Firmly attached to the plant surface
|Relatively easier to remove from the plant surface
|Feeds on plant sap by piercing and sucking
|Feeds on plant sap by piercing and sucking
|Damage to Plants
|Generally causes less damage to plants
|Can cause more damage to plants due to higher sap consumption
|San Jose scale, oystershell scale
|Cottony cushion scale, brown soft scale
Armored scales produce a harder shell that is not actually attached to the body. If you were to scrape off the shell, a soft-bodied insect would remain on the leaf or stem.
Soft scales, however, have a waxy or powdery coating in place of a hard shield, which is attached to the body.
Both types of scales feed on the sweet sap produced by plants, but soft scales excrete a sticky sweet substance called honeydew, which can attract other pest insects such as ants. In fact, a prolonged ant infestation is actually a good indicator that you could have a scale infestation.
Ants inadvertently influence the population of scale as well. An article from the Journal of Oecologia found that plants with an ant population had increased scale populations and decreased scale predators, namely, ladybugs. Ants destroy the ladybug larvae before they can grow large enough to prey on scale. Ants do this to protect their food source – honeydew!
Why Are These Scale Bugs On My Plants?
Now that you understand a little bit more about what scale bugs are, you may be wondering why they are on your plants at all. To understand this, it is helpful to understand a bit more about the scale bug’s life cycle.
As we discussed, adult scales are immobile, fixing themselves to one spot to feed and reproduce. However, when new scales hatch, their larvae are quick to move, walking, hopping, or being carried by the wind to a nearby plant on which to feed.
Scale Bugs Feed On The Sap From Woody Trees And Shrubs
The main reason that scales are seeking out your plants is to find a reliable food source. Scale bugs’ propensity for sweet sap leads them to seek out woody trees and shrubs that are rich in sap.
Scale bugs will adhere themselves to leaves or, more likely, stems and branches and bite down to reach the lower layers of wood where the sap flows, carrying nutrients to different parts of the plant.
One scale will not likely damage your plant, but unfortunately, most scales will reproduce rapidly to create a damaging infestation if left uncontrolled. Overfeeding by scale on plant sap can cause the plant to yellow and wilt, making them more susceptible to disease or injury overall.
Well-Watered Plants Are Delicious To Scale Bugs
One thing that is hard for an immobile pest insect to acquire is water. All living beings need water to survive, even scales that live most of their lives in one place.
This is because scales get their hydration through the plant sap itself. As you may guess, a well-watered plant will store much more water in its stems and branches. This extra water is enticing to a scale that may show a preference for well-watered plants over dehydrated ones.
Don’t use this fact as a reason to stop watering your plants, though! As you will learn later on, there are many other things you can do to prevent scales from populating your plants.
Sick Plants May Be An Easy Target For Scale Bugs
Most scale infestations occur on stressed or otherwise vulnerable plants. Stress can come from a variety of sources, including drought, heat stress, poor soil, or disease among others.
It isn’t totally clear why scale bugs go for stressed plants, but it could have something to do with the fact that these plants are already hosting other pests or that they are simply easier targets.
What’s worse is that an already-stressed plant is much more vulnerable to damage by pests, and their presence can make the plant more prone to other diseases or unable to bounce back from the damage that scales can cause.
Here’s How Scale Harms Plants
It’s true that stressed plants are more prone to damage by scales than more healthy individuals, but what, if any damage do the scales do on their own?
Scale Takes Resources Away From Plants
Well, for starters, scales bugs subsist off of the sap and water from plants. By making their home on plants and remaining there for the duration of their albeit short lives, they end up siphoning a significant amount of resources, especially at a large-scale infestation.
In the worst cases, this can lead to a loss of limbs or chlorosis, defined as a yellowing of the leaves from a lack of nutrients.
Honeydew Increases Fungal Growth
Scale bugs can also damage plants due to the honeydew that is produced as they feed. Not only does the sticky substance support the growth of the fungal disease sooty mold, but honeydew also attracts ants which can further damage the plant as they feed.
6 Reasons Why You Have Scale Bugs On Your Plants
Now that you understand why scale bugs are attracted to certain plants, as well as the risks they pose to your plants, you might be wondering how they have ended up on your plants in the first place.
Follow along to discover the six most common reasons you have scale bugs on your plants.
1. Scale Bugs Can Hitch A Ride On Nursery Plants
One of the most common ways scale bugs are transported from plant to plant is by hitching a ride on a nursery plant.
Even if the nursery crew is doing everything possible to protect their plants from pests, the high volume of plant matter in a nursery is bound to attract insects. It is highly likely that the odd scale bug might get missed.
Scale bugs are mobile when they are young, and the adults often house eggs beneath their waxy coverings, so once you bring them home, they are likely to spread to your other plants. You can read more about why scale can spread to other plants here.
Make sure to check a new plant thoroughly before bringing it inside or planting it in the garden. Get a good look under the leaves and in all of the cracks and crevices for any stragglers who might be hiding out.
Many gardeners will instate a quarantine period for their new plants, leaving them in another room or even outside for a few days to a week. We’ll get to some more tips for scale removal soon!
2. New Soil Is A Perfect Scale Bug Hiding Spot
Scale bugs do not live long in the soil, but they will often hide there while moving from one plant to the next as larvae. Eggs may also drop into the soil, and gestating adults can overwinter in the soil to emerge in spring with the first buds.
Soil can often be overlooked when it comes to scale because they are more often found during their sedentary adult stage of life, camped out on their plant of choice. However, if you have a recurring scale infestation that you just can’t seem to stop, you might want to consider that they are hiding in the soil.
If you do have scale in your soil, you may even want to remove and replace the first inch or two in a potted plant or consider treating the soil with horticultural oil or soap, some of the mediation techniques we’ll discuss later on.
For more information on scale in soil, check out our article on how scale insects don’t live in soil.
3. Scale Bugs Overwinter In Leaf Litter
Just like we mentioned with fresh soil, leaf litter is a common place for scales to camp out for the winter.
Leaf litter is warmer and can contain more water and nutrients than the frozen soil, and is conveniently close to the plants that scales will need to survive come spring. Also, many plants will freeze or go dormant over the coldest season, leaving the scales exposed to the winter elements.
If you opt to leave your leaves over winter to protect and feed your soil, keep a close eye on your plants as it begins to thaw out. There are methods such as sticky traps and others you can take to prevent the scales from migrating to your plants when they emerge in the spring.
While it may be tempting to remove all the leaf litter, as well as it is an aesthetic preference for many gardeners, there are plenty of beneficial insects that overwinter in leaf litter as well, and the natural predators hosted there may even keep the scale under control.
4. Scale Bugs May Latch Onto Reused Pots Or Other Garden Tools
Recycling is great, and it’s always a good idea to repurpose old pots, but they can be another source of pests like scale bugs if you’re not careful.
Due to the risk of transference, you should always clean old pots thoroughly before putting a new plant in them.
As we’ll discuss later, isopropyl alcohol or hydrogen peroxide is a great way to get rid of scale, and it’s a good idea to wipe down a used pot with one of the two, or simply clean it out with soap and water and a good scrub.
Similarly, mobile larval scales may hitch a ride on a tool while you are working in the garden. It is good practice to wipe down or clean your spades, shears, pruners, and other tools when you move from plant to plant, especially if you are dealing with any sort of pest infestation.
5. Scale Bugs Can Be Carried By Wind
Scale bugs attach themselves to plants, building a waxy or hard coat to hold them even tighter to their chosen home, but before that, they are much more vulnerable to even the slightest of breezes.
When they are scoping out potential homes in their larval stage, it is possible for scale bugs to be picked up and carried by the wind. In fact, this is one of the more common ways they transfer or move during this stage of life.
Floating on the wind can help scales cover greater distances than they could by walking or hopping, so many times, the scales will welcome the lift as an easier method to spread further and increase their territory. This can be problematic in more densely planted gardens because, on a breezy spring day, many plants can become infested with larval scale bugs.
The risk of transference is one very good reason to treat scale infestations early and thoroughly to prevent them from spreading throughout your whole garden!
6. Scale Bugs Can Simply Walk Between Nearby Plants
Given their instinctual need to spread far and wide from their place of birth, scale bugs are actually highly mobile when they first hatch from their eggs. Many animals migrate away from their birthplace in order to capitalize on fresh, untapped resources, and pest insects are no different.
It does not benefit a scale to remain on an already populated branch, especially given that the immobile adults have already depleted the plant of sap and water.
Because of this, most scale bugs will simply get up and walk to a new branch or a new plant entirely, especially if there are plenty to choose from nearby.
Detecting Scale On Your Plants
Scales are fairly easy to identify because they won’t run away from you! They get their name from their resemblance to the scales on a fish – small, circular, and flat.
It should also be fairly easy to scrape the scale off of the plant, and the armored scales will leave behind the squishy insect because they aren’t attached to the outer shell. Another good way to identify scales early in the season is to put Catchmaster Tree Shield or a similar insect tape around the base of the trunk and branches.
These traps will catch the new adults as they emerge from winter hibernation in leaf litter or soil and make their way up the plant.
Place the tape at the end of winter after the last frost, and check it regularly as the weather warms to catch scale early when they are easiest to remove.
How To Remove And Repel Scale Bugs From Plants
Now that you have identified the scale and you know where they might have come from, let’s talk about remediation. There are many effective methods for controlling and removing scale bugs from your plants.
Lady Bugs And Natural Predators Are A Good Control
One of the most effective methods of controlling scale bugs is actually natural biological control, or in other words, natural predators.
Many species of ladybugs, mites, and parasitic wasps are natural predators of scales and are a good indication of a healthy environment. Foster natural predators in your garden by cutting down on chemical control methods and instead focusing on natural biodiversity and healthy soil.
Ladybugs are particularly effective predators because both larvae and adults will feed on the scale bugs. You can even introduce them to your garden by purchasing something like Hydroponic City’s 1500 Pre-Fed Live Ladybugs.
Neem Oil Is Extremely Effective Against Scale Bugs
For more stubborn or extensive infestations, products like Captain Jack’s Neem Oil are one type of horticultural oil that is effective at removing and preventing scale bugs.
Thorough coverage is necessary to fully control an infestation, and most likely at least three treatments will be required, applied about once a week until the scales are gone. This is partially due to the protection that their outer coverings provide but also because the short-lived scale reproduces quickly and multiple generations can occur within a month.
To control all generations, multiple applications of oil or insecticidal soap are most likely necessary. We have a fantastic guide on how often you should spray scale.
Diluted Dish Soap May Help Clean Your Plants Of Scale Bugs
Diluted dish soap can work similarly to neem oil because of its viscous quality that coats and eliminates the bugs. The one caveat to soaps and oils is the risk that they can pose to the plants themselves.
Clemson University warns that water-stressed and overheated plants can actually be damaged by soaps and oils, and you should never apply them if the temperatures rise above 90 °F or in direct sunlight. The oils and soap can refract the light, leading to burns, and the oils can dry out an already heated and water-stressed plant.
Use caution when applying these methods, and take care to shade and water your plants during times of high heat regardless of whether you are treating them or not.
Isopropyl Alcohol Can Also Work
70% isopropyl alcohol can also be an effective scale removal method because the alcohol will compromise the protective coating and dry out the insect underneath.
Apply it using a dampened cotton swab or bristle brush to loosen the scale from its place on the plant.
Alcohol also has the potential to dry out or damage plants, so avoid this method when the temperatures are too hot, or drought is already a concern, and rinse off outdoor plants after application to remove any residual alcohol.
Physically Remove The Scale
Perhaps the most effective method of removing scales is by physically removing the individuals from the plants.
When it comes to smaller infestations, you can scrape or use a bristle brush to remove each insect from the plant, catching or dropping them into a bucket of soapy water to ensure they won’t find their way back. Make sure you are capturing all of the adults, larvae, and eggs when you use this method, and expect to repeat the practice multiple times throughout the season to effectively get rid of them all.
For larger-scale infestations, consider pruning the entire affected branch off the plant. Place the branch in a ziplock bag or drop it in soapy water before throwing it away.
If you’d like more ideas on how to get rid of these pesky insects, read our guide on the best ways to get rid of scale insects for good. And if your plants start to get overrun with scale and ants, you can always reach out to a pest control specialist through our nationwide pest control finder.
That’s a wrap!
Scale bugs are very common garden pests that can end up causing a fair amount of damage to your plants if you don’t get them under control. Hopefully, now you feel more equipped to identify and effectively remove them if your garden is subject to a scale infestation.
To recap, the six most common ways scales are on your plants are:
- They hitched a ride on a nursery plant.
- The scales were hiding out in the soil around your plants.
- Scales overwinter in leaf litter, only to emerge in spring.
- Scales were hiding out in reused pots or transferred via garden tools.
- They were carried by the wind.
- They simply walked from one plant to another.
Luckily, remediation can be easy. Just catch them early in their life cycle when they are most vulnerable. The best methods are to use natural predators, neem oil, diluted soap, isopropyl alcohol, or even just physically remove them.
Don’t be discouraged if you still see scales after the first treatment, because it often takes multiple applications to fully remove them all!
Bach, C.E. Direct and indirect interactions between ants (Pheidole megacephala), scales (Coccus viridis) and plants (Pluchea indica). Oecologia 87, 233–239 (1991).
Bhise, K., et. al. (2018) Plant Virus: A Brief Review. International Journal for Research in Applied Science & Engineering Technology. 6(9): 147-149.
Nile, A.S., Kwon, Y.D. & Nile, S.H. (2019) Horticultural oils: possible alternatives to chemical pesticides and insecticides. Environ Sci Pollut Res 26, 21127–21139.
Ogbuewu, I.P., et. al. (2011) The Growing Importance of Neem (Azadirachta indica A. Juss) in Agriculture, Industry, Medicine, and Environment: A Review. Research Journal of Medicinal Plant 5(3): 230-245.
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