Red Spider Mites – avoiding an invasion

Red spider mite. Something that most orchid growers will shudder at hearing. Until recently, I’d had no experience with these guys but they have arrived!

It was my Dendrobium Victoria Reginae that alerted me to them first. She had tiny little red dots on her newest leaves this morning which made me think somehow it was tiny bits of bark media. Under a magnifying glass, you can see them more clearly. They were all over the leaves and creeping down the only cane she has.

(If you don’t know what red spider mites are…click here…I can only look at these images for a short time as I start scratching!)

After consulting some orchid books and Youtube, treatment has now begun. It is suggested that red spider mites do not like moisture, so I washed the leaves under the tap and made sure I removed as many of them as I could. She was then left to air dry with the help of our floor fan. I’m also misting them twice daily at the moment, particularly the underside of the leaves.

Suddenly, I realised why some of my orchids are not doing as well as they could. Milton, my absolute favourite for fragrance, has struggled this year. His last pseudo-bulb is tiny and the leaves are growing funny. One book I consulted suggested that red spider mites love soft leaves and chew the underside of them, leaving a silvery colouring behind where they have killed the plant cells. Eventually this is supposed to turn black. The underside of one of his leaves are indeed silvery…uh oh! He is working on a new growth but it is turning a strange browny orange colour on the edges…see where I’m going with this…

Then I had a lightbulb moment. The Oncidium Twinkle I have has been struggling for months. She has black markings under her leaves and anywhere the leaves crease to form a snug hiding place. I tested her too…uh oh! She has been like this for about a year. I can only assume she has picked these critters up from when we lived in our flat and they have slowly made their way across my orchids.

The pseudo-bulbs on the Oncidium Twinkle appear to be dehydrating.

It also explains Nelly. She has the silvery underside to her leaves too, and they have been so badly damaged that they are collapsing and curling in on themselves now.

So what do I do now? I started doing spot treatments with rubbing alcohol but eventually, the systemic insecticide came out of the cupboard. Milton, Vicky, Nelly and Tinks have been treated so far, and I’ll repeat the treatment again next weekend. All other orchids have been checked over and so far no more mites (phew!).

Happy growing!

Clare