Spider Mites on Houseplants

The following questions were sent to the P&PDL diagnosticians here at Purdue University:

Question 1: I have a problem with spider mites on two large ficus here in the office. It's to the point where the leaves are turning yellow and falling off in mass. I've taken the plants outside, hosed them off, let them dry, then I drenched them in Safer Brand Insecticidal Soap for Houseplants. That was two days ago. How do I tell if I've gotten all the little monsters? Should I respray them again at any time soon?

Answer 1: Yes, it may take a couple of days to see the results of the soap treatment but you should inspect again very carefully after 5 - 7 days. If you see the tiny mites then retreat. Otherwise continue to monitor occasionally until the plant becomes healthy again.

-Tim Gibb, Entomologist

Question 2: I have spider mites on my houseplants! I've been told that the problem originated through the potting soil I was using. Unless the soil is sterile, there's a good chance that the eggs of these mites are most likely present. I'm not comfortable enough to have my plants completely rely on me for their food, so, sterile soil is not the answer for me. How would you most effectively handle the mites in a safe (non-toxic), and simple manner? I've heard about using predator mites, but how?? Where do I get them? Please keep in mind that I have pets and wish not to endanger their health either.

Answer 2: The spider mites are not likely to have come from the soil. They probably came in from other plants before or after you purchased them. For mites I recommend trying either insecticidal soap at 2%, or you can release spider mite predators. The best predator to release is Phytoseilus persimilus. I have had good results purchasing them from IPM Labs, Inc. in Locke New York. 315-497-2063.

-Cliff Sadof, Extension Entomologist