We’ve struggled with spider mites in the past. Nasty pests. But this was a new one for me.
False spider mites.
We started to see damage on our mint at the end of March. Necrotic (dead) areas along the margins of the leaves and sometimes a whole leaf. This looked similar to some spider mite damage on mint that I’d seen before so I put out extra californicus mites that I happened to be distributing at about the time I noticed this problem.
I should have looked at it more carefully.
After about a week I looked at the leaf under a microscope and found some tiny red mites with black spots somewhat similar to spider mites (except that they were red and small). I called the sales rep who deals in bugs for us. He said that spider mites coming out of diapause (invertebrate hibernation) often looked reddish coloured so I ordered some persimilis mites to deal with the spider mites. (I use californicus for prevention and a small amount of control because they can live pretty long without much food if needed, and persimilis for outbreaks because they are more aggressive eaters but starve quickly if there’s no food).
A few weeks later the sales rep came out to the greenhouse and I showed him my weird, red spider mites. He said, “I don’t think these are spider mites, but I have no idea what they actually are.”
An entomologist reading this might think it’s interesting to have different kinds of bugs than they’ve seen before. As a grower it’s pure stress. Might as well have a doctor tell me that I have cancer but they don’t know what kind.
Several photos uploaded and phone calls later, “false spider mites.” (Latin name: Tenuipalpidae Prostigmata). It didn’t sound so bad.
“So how do I control them?”
“There’s no known biological control. There are some sprays that work.”
Since we don’t spray conventional chemicals this was depressing news. A few days later we put each mint pot in a garbage bag and pulled the whole lot out of the greenhouse. We mixed a strong soap solution and sprayed the whole area numerous times over several days.
We dumped the contents of the pots at the far end of the field, and those bins are currently sitting empty 100 feet from the greenhouse ready for a serious pre-washing and sanitizing before bringing them back into the facility.
It has been about 2 weeks since the mint exodus, and I have seen no evidence of the mites (knock on wood) since. It seems to easy. I keep scouting the area, but these mites are very small so it may be that there will have to be enough to do damage before we see how far they’ve spread.
I took a lot of pictures attempting to capture a good picture of the mite for identifying to the entomologists, but they make very poor models. Not only do they move when they are supposed to stay still, but they are tiny (even under my microscope). I will include several here to try to give an idea of what you are looking at, but there are better pictures elsewhere on the web.