If you are a collector, I think you have to assume that you have flat mites on at least some of your plants. You also have to assume that any new plant or cutting that you take in will have them. If you grow outside almost exclusively, I believe that frequent sprayings with the hose and natural predators of these mites can keep them at bay to a degree, but if you exclusively grow indoors, you will have a problem at some point.

I cannot tell anyone what they should do, but after only 3 weeks spraying everything with sulfur has made a huge difference for me. The number of Hoyas putting out new growth that have not grown for a very long time is remarkable. A couple of examples: H. serpens is throwing out crazy growth from many points when it just sat there for months. H. sp. Timor Leste had not done anything for months and had some yellow spotting on the leaves, sending up new leaves and vines. The same thing can be said for H. sp. Gunung Gading, H. undulata, and H. ruthiae. I would say that 90% of everything that I had that was either not growing or growing almost not at all is throwing out new growth. Below a photo of H. serpens that had not grown in months, and one that I have greatly struggled with over the past few years is busting out with new growth.

It has now been three weeks since spraying with sulfur; lets discuss what to expect. First there has been zero phytotoxicity; there has been no leaf drop even on the tenderest of new growth on any plant. At first the smell of the sulfur is kind of overwhelming, but over time it will dissipate somewhat. Still in the morning when I first open my tent, because of the high humidity, I have to wait a few minutes before entering as the sulfur smell is pretty intense.

Flat mites are insidious because they are invisible to the naked eye; this is why most growers don’t realize they have a problem. While seeing them without magnification is impossible, the damage that they cause is readily apparent. When a Hoya ceases to grow for long periods, and there are many nubby points where the plant tried to grow, but is unable, you most likely have flat mites. Look at the photo below for this failure to grow with nubs that I am talking about in a 2 leaf cutting of H. sp. Gunung Gading:

The damage in the circle and the leaf damage to the right are clear evidence of flat mites. The only reason that I have not thrown this plant out is because the roots are in terrific shape with no rot present.

I have lost a lot of plants over the last few year to what I blamed on my own incompetence as a grower. I always thought that I made some watering mistake that stopped a plant from growing, or the fertilizer was not right, or the temperature was too cold; there was always something. There were so many plants that I put into a list that I called Plants That I Could Grow Well At One Time, But Cannot Grow Any Longer To Save My Life. I now believe that most of my issues were because of this invisible menace – the flat mite.

I opted to spray every single plant that I owned whether it was growing gangbusters, or whether it had not grown for a year. It was an enormous task that took me three days to complete. I went through gallons of spray and saturated every surface of the plant; it did not matter if it was a small cutting in the process of rooting or a four foot tall plant it got sprayed. Fortunately it was still warm enough to spray outside when I learned of this issue in mid-September. Below some of the sprayed plants in one of my tents:

The very nice woman who told me that I had flat mites said that she was ready to give up the hobby because of them until she finally found the solution to the problem. She gave me several options for dealing with them, but some of the miticides were so dangerous to use, I opted for the organic least toxic alternative that she had used on her own collection. I chose to spray with sulfur; the same one that pictured below:

I recently sold some cuttings to a woman from Nevada that carefully examined them with a hand held digital microscope that wirelessly connects to your phone see photo below:

She told me that she found flat mites and did not want to make me feel bad, but thought that I should know so that I could take remediation steps.

I have quietly been pursuing my passion for growing Hoyas for going on 20 years now, but up until now have been bothered by relatively few pests. My primary pests until now were fungus gnats, a few plants that were susceptible to spider mites, and a few aphids. Knock on wood I somehow managed to escape mealie bugs and root mealie bugs. I think I have so little problem with pest, because I bring in very few new plants into my collection every year. I read with horror the new issue of STEMMA on Facebook recently with its cover story talking about flat mites and hoped that I would never get something so insidious! The image below was copied from this Wikipedia Article: https://en.wikipedia.org/wiki/Brevipalpus_phoenicis#Control

Several months ago I started over my Hoya blashernaezii ssp siariae as it was languishing and not growing. I think I now know the reason for it – the dreaded flat mite! After spraying my entire collection with sulfur, this plant is one of many that has absolutely taken off, and is growing better than at any time. The white spots on the leaves are sulfur residue. Much more on my flat mite experience at a later date!

I am so in love with my Hoya linearis plant that I have to show it off one more time. It actually has nine peduncles with open flowers.