A Mite for A Mite: Predatory Mites for Orchid Mite Control

If you grow orchids, you are almost certainly going to run into pests. Starting this winter, I have been noticing what looked like mite damage on some of my orchids. Initially, it was just one plant, which got cleaned with soapy water. Then, I noticed them on an adjacent plant, then another. I treated with soapy water, which did work temporarily, but they would come back. Spraying the leaves with isopropyl alcohol also has a temporary knock-down effect, but the mites return. 

Because there was no webbing present I suspected a species of flat red mite, or what is sometimes called "false spider mites." These are tiny and can only be seen as a rusty dusting, and by the damage they cause. 

Mites and mite damage on Phalaenopsis stuartiana in my collection. This plant does have some spotted white stripes on the leaves, but the pitted look in the leaf vein and near the top edge of the leaf is mite damage. The mites aren't individually visible to the human eye, the slightly rusty coloration around the damage is congregations of them.

It is widely reported that increasing humidity will knock down populations, but for my particular mites, this has not been true. My phalaenopsis grow on tented shelves and get misted twice a day, which is about as much humidity as I think they can take. 

Mites and mite damage on a hybrid NOID Phalaenopsis. The white pitting is mite damge, and the rusty bits are congregations of mites. 

Mite damage and mites on the central column of a hybrid Phalaenopsis orchid. The white pitting is mite damage, and the rusty coloration is the mites. This plant is clearly stressed, and is dropping its two lower leaves as a result.

A common way to test for mites is to wipe a suspected area with a white tissue. Rusty dark specks are mites.

My particular population of mites seems to prefer Phalaenopsis orchids. I have noticed mites on a couple Cattleyas, but those have so far been very limited and wash with soapy water clears it up. Recently I pulled out the family microscope and captured a few on slides to take a closer look. 

I am certainly no expert, but the preference for the Phalaenopsis genus and the appearance of the mites looks a lot like images of Tenuipalpus pacificus. In fact, this looks rather like the example female shown on the University of Florida "Featured Creatures" website. 

This mite looks a bit beat up, missing some legs and antennae.

Perhaps an immature stage of mite- maybe an egg?

In researching mites, it seems that they are not affected by most pesticides-- a specific miticide is necessary. In the US, it is possible to purchase miticides such as Avid, but they are quite toxic and I grow my orchids inside my house and have young children. 

Therefore, I decided to try predatory mites. In my research, Amblyseius swirskii seemed to be a good predator for my suspected mite population. I decided to hit them hard with 4,000 live mites and 10 slow release sachets to keep up the pressure. The 4,000 live mites come in a little shaker filled with bran. Apparently the bran creates a habitat for the mites and provides bran mites to keep the mites alive in transport. 

According to the directions, you should release as soon as you receive your mites, and preferrably at night when the plant lights are off. You can buy little boxes to put the bran in, but I went for the direct method and shook it onto my plants. After a couple of days, I cleaned them off by shaking it off or spraying with water to clean the leaves and stems. 

The slow release sachets can be hung on the plants or the plant pots. I have tried to hang them where the pest mites were most active, and under the leaves to protect them from light. 

It is probably just a coincidence or a psychological effect, but it seemed to me that I was seeing a flush of new growth only days after the introduction of the mites. It has now been 3 weeks, and I have seen very few live mites. The sachets only last 30 days, so I plan to introduce some new ones shortly. 

Unfortunately, I have lost one plant that was badly affected by mites and wasn't doing so great to begin with (Phalaenopsis Kaoda Twinkle), but the others (there are more than 50 phalaenopsis in my collection) seem to be recovering and moving into their summer growth cycles.