Flat Mites: How to Identify and Treat Flat Mites for Hoya Growers

Flat mites, or false spider mites, have become the topic of many conversations in Hoya circles over the past year and a half because many of us were finding out that these mites existed and realizing that our plants had been suffering from them for a long time.

As soon as I learned about the signs and symptoms of flat mites, I knew they had plagued my own collection for years.

I had actually given up on several plants I could have saved if I had known that the problem was flat mites and not my inability to grow some hoyas.

I’ve heard other hoya growers, like Doug Chamberlain from Vermont Hoyas, express similar stories.

Doug discusses how he believed certain hoyas were difficult to grow when it was actually flat mites impeding hoya growth. I’ll link Doug Chamberlain’s story here, in case you’d like to read it.

This week we will discuss how flat mites affect Hoyas and how to identify, treat, and prevent them.

Much of the information in this post is gleaned from fellow growers, my own personal experience, and Stemma Journal, “a freely circulated downloadable pdf publication about the genus Hoya.” The quote is from the Stemma Journal’s facebook page, which I will link here so anyone interested can join.

It is a wonderful source of information for those passionate about growing and learning about hoyas!

Table of Contents

Hoyas are my favorite plants & I nearly gave up growing most of them because of flat mites

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Long before I knew flat mites existed, many of my hoyas weren’t growing. I had worked hard to root cuttings and lovingly water them only to watch them sit like statues for years. Truly years.

I began to demote these plants that I once loved because I found less and less joy in growing them. My space and time became increasingly limited as I had children. I had to start making hard choices about which plants to keep and which plants to let go of for my growing family and responsibilities.

Eventually, I composted many plants that I considered failures and began to consider myself a person who couldn’t grow many hoyas. I still had a large collection (considering what most people might think of), but compared to what I had at one point, I had probably cut the plants if half.

It’s really sad when I reflect on it because the plants were “healthy” outside of having mites, but I had no way of knowing.

Meanwhile, I concentrated my growing efforts elsewhere and found lots of growing success with even very difficult-to-grow houseplants, such as fruiting container plants, herbs, sensitive anthuriums, etcetera.

It never occurred to me that my growing skills might not be the problem– that a microscopic infestation might be until I heard about the flat mite.

Why are Flat Mites a massive problem for Hoya growers and lovers?

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Flat mites can’t be seen with the naked eye. They truly cannot be seen without a microscope or a very strong hand lens. Even then, they are so small that they are easy to miss.

Despite their tiny size, they cause plants to suffer greatly.

Affected plants will often stop growing or drop new growth, develop scarring on the backs of the leaves, develop nubby growth where nodes are incredibly close together and leafless, or put out vines that never develop leaves.

My experience with them has been like having hoyas statues– plants that are frozen in time.

Flat mites do not just infest hoyas

It is important to note that flat mites can affect other plants- not just hoyas!

I did not know this until asking growers very recently. Yikes.

Most, if not all, of our houseplants are susceptible!

I’ve read of people finding them on philodendrons, calatheas, anthuriums, African violets, and more.

They are also a well-known problem for orchids, as much as they are for hoyas.

So, if you have an extensive collection like I do, be sure to take note and check your other plants as well!

How to Identify Flat Mites

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Flat mites (in the family Tenuipalpidae) are arachnids, like spider mites (in the family Tetranychidae). Unlike spider mites, they do not create webbing and cannot be seen without a microscope or high-powered hand lens.

Even with a microscope and high-powered hand lens, they can be challenging to find because they are so tiny.

The good news is that they are orange or red, which makes them easier to spot than the other sneaky microscopic mite that plagues hoyas (the broad mite), whose green or yellow appearance renders them nearly invisible.

Two ways to identify flat mites:

#1 Look for symptoms of flat mites (the most common way to identify them)

If you see several of the symptoms below, it is very likely your hoya may have flat mites and may benefit from treatment.

  • Scarring where the leaf meets the petiole (looks like crusty, brown formation)
  • Scarring on the backs of the leaves (looks like crusty, brown formation)
  • Plants that aren’t growing and haven’t grown for a long time
  • Nubby growth where nodes are close together, kind of thick and ugly
  • Plants may produce vines but never end up producing leaves
    • It is common for some hoyas to produce long vines before growing leaves on the vines, but if it has been six months or longer and the plant still hasn’t produced any leaves on the vine, it might indicate an issue.
  • New leaves drop with seemingly no reason

I often do not need to see the mite itself to know it’s there.

If I notice several of the symptoms above plaguing a plant (or even just a plant that isn’t growing), I will often treat it for mites. This assumes that the roots and foliage seem healthy otherwise and that the plant is receiving an ample amount of light and water. In other words, this assumes that the hoya is in good growing conditions.

#2 Use a strong hand lens or microscope to look for them around plant crotches and new growth

USB Digital Microscope (linked to Amazon*)

compatible with iPhone, Android, Windows, Mac

Hand Lens – Jeweler’s Loop (linked to Amazon*)

2 Pack, with LED light

*products above are linked via the Amazon affiliate program, which means I may make a small commission if you use the links provided. This is at no cost to you. Any earnings go back to directly support this blog. Thank you for your support!

Below are photos of flat mites under magnification. I took these using the microscope pictured above. The first two sets of photos are from Hoya obscura, and the photos that follow are from Hoya carnosa ‘Nova Ghost’.

I circled flat mites in purple and a possible predatory mite (a good guy) in blue! It’s also possible this was not a predatory mite and just an adult flat mite. I like to think it was a good guy though. 🙂

Some other flat mites are hiding in the pictures below that I did not circle. Can you spot them?

Such sneaky little pests.

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Here are the photos from Hoya carnosa ‘Nova Ghost.’ I will include photos of the plant just before using the microscope. I tried to take crisp, clear images using my phone so you could see what the plant looked like and whether you could spot the flat mites without using the microscope.

Note the failed growth point on the plant. It’s been a one-leaf wonder for a long time. Here it is under magnification:

Look whose here. Darn it.

At least there aren’t too many… yet!

How to Treat Flat Mites

There are three important notes when choosing a treatment for flat mites.

Note #1 The first is that flat mites are not insects. They are mites and are part of the arachnid family. This makes any treatment that is geared toward insects specifically likely not to work.

Note #2 Second, not all treatments recommended for spider mites will work for flat mites.

Note #3 You must consider the lifecycle of flat mites when treating them. Flat mites have a 6 to 8-week lifecycle. Eggs can take several weeks to hatch. Larvae can take up to 6 weeks to become an adult. The long lifecycle of flat mites requires a long treatment schedule as well, one that spans at least 6 weeks or more.

There are lots of treatment options with varying degrees of success. The two options that seem to have the most success stories are what I will list here.

In the introduction, I linked Stemma Journal as a wonderful resource for learning more.

In the July 2022 publication, there is a featured article by Rebecca Lance on flat mites where she lists out many more treatment options and discusses their effectiveness if you are interested. I will link it here!

Option #1 Sulfur treatment

Sulfur is sold as a powder for use to control fungal and bacterial issues as well as some pest issues. One of the pests that it is extremely effective on is flat mites!

To apply sulfur, mix the sulfur dust into water and spray it onto your plants according to the directions on the bottle.

You have to coat the entire plant, all surfaces, for the treatment to be successful.

This process ideally needs to be repeated about weekly or bi-weekly for 6 weeks or more to eliminate all stages of the mites.

The photo above is linked to Amazon through the affiliate program, which means I may make a small commission if you purchase using this link. Anything I make will be at no additional cost to you and will 100% support this blog.

Option #2 Predatory mites

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Predatory mites are my preferred option for treating flat mites, but I want to be clear that predatory mites do not eliminate flat mites. Instead, they manage the populations so that the flat mite populations remain small enough not to cause major growth restrictions and other issues for Hoyas.

If I want to find flat mites on my plants or take pictures of them for a blog post (like this one), I absolutely can. Because they are still there, despite releasing predatory mites regularly.

Because predatory mites do not eliminate flat mites, helping to control populations through other means is advised.

One easy way is by simply showering plants with strong water sprays to remove some of the mites. This is good practice for controlling other pests, diseases, and dust buildup over time as well.

Predatory mites eat various pests depending on their preferred diet. Some eat spider mites, various forms of thrips, whiteflies, broad mites, etcetera. They are a form of natural pest control.

These “good” mites also have certain preferences regarding humidity and temperature, so some thrive better than others in home environments.

I prefer to release several varieties of predatory mites, but the one that is supposed to be most effective at eating flat mites is Neoseiulus californicus, which can do quite well in household conditions.

Vendors that sell predatory mites, like Nature’s Good Guys or Arbico Organics, will tell you how many to release per square foot for infestations versus prevention, and you can decide what you prefer.

You can also choose whether to buy adult mites that are live upon arrival or slow-release packets that are eggs that will hatch over time.

If you are trying to eliminate populations more quickly, starting with adults versus waiting for eggs to hatch is typically better.

Check out the amazing video below of a predatory mite helping to eliminate a flat mite. Wow!

How to Prevent Flat Mites

Shower plant off in the sink

Quarantine new plants and watch for any signs of flat mites

You may want to use a hand lens or microscope to look for flat mites themselves.

To be extra safe, applying treatment to a new plant as if it has flat mites is a great option. This is particularly wise if you’ve done the hard work of treating your entire collection and ridding it of flat mites.

Simply showering plants off thoroughly when watering can do a fair amount to decrease and control populations of all pests, including flat mites.

And, of course, keep an eye out for signs and symptoms so any affected plant can be separated and treated.

I personally assume that any new hoya has flat mites. I have also seen hoyas for sale in local greenhouses that have the characteristic scarring from flat mites and knew this meant that those plants and probably all the plants around it were infected.

These mites are so common that it is better to assume they are present on a new plant than to believe they are not.

Particularly because we cannot see them with the naked eye, no matter how hard we try, we cannot rule them out without microscopic inspection.

Happy growing!

For People Who Are Obsessed With Hoyas

Hoya obovata: Care Tips and Personal Experiences

Heirloom Hoya carnosa: Care Tips, How to Root Cuttings, and Personal Experiences

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