Tony O’Neill, gardener and author of the popular “Composting Masterclass” and “Your First Vegetable Garden,” combines lifelong passion and expert knowledge to simplify the art of gardening. His mission? Helping you cultivate a thriving garden. More on Tony O’Neill
I can think of the dreaded spider Mites as nothing more soul-destroying than getting rid of Spider mites on your plants.
The horror of horrors… how could anyone who has been growing plants for a couple of years does not know of this terrible affliction that can destroy an entire plant (Spider Mites)?
Easy, Very Easy!
The first issue is that these spider mites are tiny, so it is easy to miss them unless you’re looking for them.
Also, If you are new to gardening, you may not know what to look for when looking for spider mites.
Worry not; by the time you finish reading this article, you will know precisely how to identify if your plants are suffering from spider mites and how to deal with spider mites and prevent spider mites from returning.
You are in the right place. I have you covered!
With just over 1200 species of spider mites worldwide, they can be a pain for the gardener; they are small and live on the underside of leaves, so they are hard to spot.
They spin fine webbing for protection, Damaging plants by piercing the leaf cells to feed.
What Are Spider Mites
When I started gardening, I had no clue what spider mites were; however, I saw the signs left behind from the spider mite damage they caused.
Read on to learn what you need to ensure these tiny spider mites don’t ruin your plants at home. Here is what happened to me!
Mea culpa. I brought a plant to a show showing evidence of these spider mites on the leaves. How could you do such a thing, you may well ask?
The answer is simple… I had never seen them, didn’t know what spider mites looked like, was unaware that my insecticide was little or no use against them, and despite asking more expert growers than me, was still as ignorant of the pest as when I started.
Suddenly, I was introduced to the Spider Mites and Two-spotted spider mites.
I had no idea how to deal with these problems; these spider mites were sucking the life out of my houseplants and the vegetables growing in my garden.
I did some research, unaware of these spider mites and how to identify and find them.
Over the past 40 years, I have gained a lot of information and combated and won many spider mite outbreaks.
What color are spider mites?
Most people would say RED, of course. Some say they are black; some say green. Therefore if you are checking your plants, you will know what you are looking for… or will you?
This has got to be one of the biggest misnomers guaranteed to mislead the unwary. SPIDER MITEs, for example, are only RED at a certain year stage, after hibernation and springtime.
The newly hatched spider mites are white (off-white/buff-colored); the adult spider mites can be white (but in varying degrees through to green) with two spots on their back, looking like a saddle.
These spots are considered dark green or red, so dark that they could be taken for black.
But these are only spots and not the whole insect. It is also known as the Twospotted Spider Mites.
Other spider mites are sometimes found on plants indoors, and that is the Carmine Spider mite, but I haven’t seen that one yet, so I don’t know how it develops.
What Are Red Spider Mites?
Red spider mites are tiny, crawling, wingless insects (well, actually, they are arachnids for those who like to be pedantic about semantics) with 6 or 8 legs depending on the stage of development.
Juvenile spider mites have six legs, and adults have 8.
They are so small that they are invisible to the naked eye, and a magnifying glass is needed to see them.
This is why most people are unaware they have an issue until the leaves on their plants start turning yellow.
If you imagine the full stops I have just used, spider mites are more challenging to see than that.
Twospotted Spider Mites – Tetranychus urticae Koch
The Twospotted Spider mites are oval, ranging from translucent to brown, but yellow is the primary color they are found with.
Given their name (two-spotted spider mites) due to the two large spots on either side of the abdomen.
These are found throughout Europe and the USA and can have outbreaks that can decimate the plants in your home.
Spruce Spider Mite
The Spruce Spider Mite is small, and you will need a 20x magnifying glass or microscope just to see them; they also cause high levels of spider mite damage to Conifers trees, Balsam Firs trees, and Spruce trees, which gives it its name.
These mites can reproduce very quickly and only take 5 to 8 days from spider mite eggs to breeding adult age.
Infestations can occur quickly, especially during hot, dry spells, destroying the entire plant.
Adults can lay eggs from only 36 hours old!!! The eggs are more easily seen with the magnifying glass as they are laid in small clusters, usually close to the veins of the underside of the leaf.
You may also see the adult two-spotted female close by, as she will lay about 5/6 eggs daily.
However, as I mentioned, it speeds up, dependent on temperature.
One account I have read suggests that at 60 degrees, she produces 20 offspring; at 70 degrees, she and her offspring number 13,000; and at 80 degrees, she represents a potential 13,000,000 individuals, all within one month!
This is a significant problem in the making, as the short breeding cycle (as little as eight days from an egg to an adult breeding pest) combined with the early ability for the young to procreate means that a massive infestation can arrive in a tiny space.
Hence the reason for the paranoia surrounding this pest!
What Conditions Increase Spider Mite Infestation?
Simply speaking, the heat of the greenhouse speeds up the life cycle. Spider mite populations can explode very quickly.
It can be as short as three days in hot places and as long as a month in cool weather.
So clearly, the temperature and a dry, dusty atmosphere are critical to the proliferation.
As Greenhouses tend to be warming up considerably from April, it is about this time that the breeding goes.
Severe spider mite numbers are inevitable unless controlled, and it will continue until autumn, given the conditions when it tends to slow down as plants begin to take on dormancy.
The remaining females will turn RED (described by some as more orange than red) and find places to hibernate.
This is likely to be in the soil or compost of the host plant, in the bark of mature plants, or in the wood or brickwork of the building itself. They are incredibly tiny, so no crevice is too small for a winter home for them.
They will re-emerge in the spring and be bright red (or Orangey red).
A cooler temperature and moist atmosphere slow their metabolism and reproductive rate, so misting and capillary matting may help control spider mites.
Spotting Spider Mites On Your Plants?
As with most pests, they will be found underneath the leaves, so they have to be looked for regularly. But you can’t see them, can you?
On close inspection, you will see the effects of the eggs from above.
The hatching young will eat away at the underside of the leaf, sucking the life out of the plant, and this sometimes leaves a visible mark through and onto the top of the leaf.
This may be yellowish or silvery and will be a small cluster of spots, each about the size of a full stop, and only by the fact that they are clustered does the mite give itself away.
Most of us don’t notice mites until the infestation is established and the plant has been damaged. Leaves of affected plants seem to be drying out very quickly, which they are, as the mites suck the very life-giving sap from them.
Dead and dried-out leaves fall, and the plant begins to fade away.
As the adults colonize the plant, they may also spin an excellent web over the leaf from branch to branch and, alas, from plant to plant.
At this stage, you must take drastic action.
This enables them to walk down the host plant across the compost, over the bench or floor, and onto the next victim. Real serial killers these are.
The webbing also tends to act as a shelter for the young underneath the leaf so that the effectiveness of sprays is considerably reduced.
14 Steps To Combat Spider Mite Infestation
1) It is about his time that a pair of kneeling pads becomes useful, as you may have to refer to praying before the spider mites problem is solved! Just kidding…
2) Most importantly, prevention is better than cure for spider mites, as I have found to my cost.
If you can cut off the source of supply, you are on your way to preventing an outbreak of whatever mites are in your greenhouse. It will save you from treating it.
Place a “bug screen” over open windows and doors to stop the ingress of pests while still allowing air to circulate.
You will almost certainly become aware very quickly of how effective this is in keeping down the number of insects getting at your plants in the first place.
I replace whole glass sections with this screen, which helps keep the temperature and airflow up!
Replace the glass in the greenhouse door with a screen, and you can ignore the advice to “leave the greenhouse door open on hot days.”
3) Remove any infected plants with spider mites immediately… if you can afford to lose the plant, burn it or get rid of it… don’t throw it into your compost bin, which may lead to re-infestation.
You may be fortunate enough to get a “clean “cutting or two” before disposing of the plant, but let that be a lesson to you and think of it as part of the learning curve.
4) Check your plants regularly for any tell-tale signs of spider mites. Pick the plant up and look underneath the leaves using your magnifying lens, and you may see the spider mites moving about or eggs clustered.
You will look for other insects, so use the magnifying glass to check for spider mites. It may seem obvious but don’t buy infected plants.
And DON’T bring infected plants with spider mites to the plant sale.
Do not be afraid to get out your magnifying glass and check out any plants you are about to buy for spider mites! It will save you time, effort, and expense in the long run. I, for one, will always carry my glass to plant sales in the future.
5) Keep a generous space between indoor plants to prevent spider mites from dropping from one plant to the next… This is true for most crawling pests too.
This is probably the most significant fault we “space-restricted” amateurs have. We cram too many plants into our small greenhouse or growing space, bringing most of our problems upon ourselves.
So how many indoor plants is it possible to have in a 12 x 8 greenhouse? Good question. How does about 30 or 40 sound? One “Expert”
As a broad rule of thumb, one 5” pot will contain a plant 15” in diameter. If you leave a 3” gap between indoor plants, you will need about 18” square for each fully-grown specimen.
A 6” pot, therefore, requires 21” square and a 7” pot will need 2ft square, and so on… Easy to see how the space is quickly used up…
6) If you are lucky, you will find a spider mites problem early and have a good chance of eradicating the issue by simply squashing the spider mites and the eggs between the finger and thumb, but I find that this always tends to damage the leaf.
7) Try washing off spider mites with a strong water sprayer. Some people use soapy water for this…but you should cover the surrounding area under the plant to catch any spider mites that fall from it, as they could infect other indoor plants.
8) Improve the conditions in the greenhouse with more misting and cooler temperatures… this may be a bonus for Fuchsia growers as the more complex you can grow the indoor plants, the better they seem to like it.
If you can afford it, install a watering and misting system. Together with capillary matting & increasing humidity by hosing down the hot greenhouse floor, you will almost certainly keep spider mites at bay.
Be careful about increased humidity as this can lead to botrytis if allowed to cool down too much, particularly at night.
A cold, humid atmosphere will undoubtedly lead to increased botrytis problems.
You need to strike a balance between heat and humidity.
9) Introduce Biological controls – predatory mites. Predatory mites can eradicate spider mites PDQ provided they are introduced early, i.e., before the infestation is out of control.
Other predatory mites feed directly on the spider mites and will devour them rapidly.
The predatory mites should gain control in about four weeks, by which time they will have eaten all the spider mites, and then the predatory mites become cannibals and eat each other until they, too, have all gone.
I understand that predatory mites are expensive, but it’s worth it if it puts you back in control. The secret here appears to be to introduce the predatory mites before the spider mites problem gets out of hand.
If you use predatory mites, you must stop using insecticides, as they kill your precious beneficial insects.
There is a waiting period between your last spray and your first introduction to predators.
10) Some people regard chemical sprays as less effective, but Polysect is reputed to be a reasonable control against spider mites and other pests.
Read the label carefully; you will see that differing strength mixes are required for treating various spider mite populations.
11) It may be possible to place sticky paper traps cut into strips around the pots to prevent the spider mites from emigrating from plant to plant. This will stop mites in their tracks.
12) Hot pepper wax – sprayed to prevent transpiration – is another remedy that smothers the adult spider mites on the leaves but does not kill the mites’ eggs.
So, it is prepared to repeat applications every four or five days until control is established.
Spider mites need to expire a lot of moisture from their bodies to survive.
If you can affect this, you are well on overcoming the mites problem.
This Hot pepper wax is also a brilliant repellent to white, black, and greenfly, as they do not like the Peppery taste of Cayenne! It also makes the leaves shine which is another bonus.
Again, a little expensive initial outlay goes a long way, so you don’t need much. I love this stuff! And it is ideally “Organic.”
The cayenne powder, sprayed onto the compost surface in your pots, is also reputed to deter crawling insects or sciarid flies, but I have yet to try this. Sciarid is a pest that I have very little trouble with anyway.
However, it may be an organic deterrent to Vine weevils crawling onto your pots so that it could be worth the try.
As an aside, the chopped & dried stems of tobacco plants are used by cage bird breeders to keep spider mites at bay.
The stems are incorporated into the nesting material, creating an inhospitable environment for the insects.
If you grow tobacco plants ( nicotiana), you only need to hang up the plants to dry as you would with any dried plant, and you will have your supply.
And in case you want to know –yes, you can smoke tobacco, but that can be the subject of another article.
Nicotine in the form of snuff is also an insect deterrent when sprinkled on top of the compost – it must make them sneeze!
Remember, though, that tobacco is high in nitrogen, so if you are one of the very fussy people who make your potions for compost, it may upset the balance of your mix.
Very little is needed, and this should not be a problem.
13) How often have you ignored a mark or blemish on a leaf because there was no easily identifiable cause? I have.
Sometimes the culprit has gone and is now doing damage elsewhere.
Or is he… Perhaps he is just too small to spot.
If you have a marked or damaged leaf, remove it without much disturbance.
You will get rid of a significant spider mites headache about to fold.
14) The Internet has some good articles if you want to go that far. Smothering the spider mites seems popular and may be worth the effort.
I have taken these recipes from a website and haven’t any reason to doubt their effectiveness.
Sub-Family Bryobini, Hystrichonychini, and Petrobiini.
Sub-Family For Eurytetranychini, Tenuipalpoidini, and Tetranychini
Spider Mite Damage to Plants
Spider mites damage may be difficult to spot initially until the numbers increase.
As time goes by, if they are not spotted, a spider mite infestation will occur, and this is when the gardener will spot the symptoms of an outbreak.
You will first see the signs of yellowing leaves at the base.
The underneath of the leaves will be a fine webbing. It is this webbing that forms protection for the spider mites as they feed sucking from the cells of the flower or leaves.
The leaves will turn from green to yellow or even grey.
When gardening in your garden, keeping an eye out for the webbing when performing maintenance is essential.
Unless you catch this early enough, an infestation can damage outdoor plants, reducing their productivity and killing your plants at home.
Remedies For Spider Mites
There are many remedies for spider mites that you can buy. These include chemical sprays, insecticidal soaps, and Mechanical and Bioactivity.
Mechanical is straightforward, which is a maintenance side of this process; washing the leaves with a spray of water can knock the two-spotted spider mites to the ground; it raises humidity, which is not conducive to spider mites.
Chemical, Insecticidal Soaps, and Bioactivity Treatments
There are various purchased items for the treatment of spider mites. As a natural and organic gardener, I tend to air on organic products when treating outdoor plants.
Still, if you are infested and cannot control spider mites by any other means, you may have to resort to a chemical formulation.
SB Plant Invigorator is an insecticidal soap perfect for dealing with spider mites.
I use this all the time, along with Neem. Consider looking out for both these products as they are both organic.
Biocontrol of spider mites is another popular method but can be a little more expensive.
3 Homemade Spider Mite Insecticidal Recipies
Spider Mite Spray. 1
For this natural spider mite spray, blend the following
½ cup of starch or flour
½ cup of milk
When sprayed over the mites, this mixture will trap them as it dries into a thin film. Repeat every 4/5 days until control is established.
Check plants daily to ensure effectiveness. Dead mites will turn black, so they are much easier to see.
Spider Mite Spray. 2
This is also a natural deterrent to uninfected outdoor plants and may help to keep mites and another pest at bay. It is also good to ward off Vampires.!
½ – 1-ounce Garlic
2-3 ounces of onion
½ – 1 ounce of cloves
½ – 1 ounce of Cayenne pepper
Whiz in your blender with 1 Cup of water till very fine.
Add this mixture to one gallon of room-temperature water.
This natural spider mite treatment spray must be repeated three times at 5-day intervals to kill off freshly hatched mites (the spray will not kill the eggs). If the mixture gets washed off, it must be re-applied.
Spider Mite Spray. 3
This is the favorite of the person who posted it on the website. It is a product called natural “Ultra-Fine.”
This natural soap and phosphorous solution is intended to kill Spider mites and their eggs (as well as most other common pests) with just one spraying.
Repeat after ten days as a precaution in case you missed any the first time.
I have contacted a guy in America to see if this is available in the U.K., but I am still waiting for a reply.
I will be on the lookout for this one, as it seems to be what I/ we need!
Once control is assured, I think I will try the biological methods… perhaps a few Praying Mantis, which will eat every other insect known to us gardeners, and I think I know a lad around the corner who keeps them as pets.
We may be able to do a deal…hmmm.
The video below can help you when dealing with Spider mites
Pests That Can Affect Your Plants
Spider mites are a nightmare when it comes to damaging your plants, But there are so many more pests and diseases, such as Whiteflies, Fungus Gnats, Hornworms, Termites, Rats, Blackflies, Aphids, Allium Leaf Miner, Ants, Thrips, Slugs, and Flea Beetles, just to name a few.
Learning each of these pests and how to deal with them can significantly increase your chances of having a successful garden.
It is important to remember that prevention is better than cure to prevent spider mite damage.
Don’t just pick up a plant and bring it home. Check for spider mites, and leave the plant in the nursery if you see them; it will save you from treating them.
Take your magnifying glass when you buy plants – no matter where from – and check them thoroughly.
Try not to move plants in and out of the greenhouse as you could be carrying in the latest infestation.
I hope this article is of help to get rid of spider mites or to kill spider mites to others like me who know very little about Spider mites and have a chance to learn before the problem arises.