Spider mites: A fine web of trouble
August 26, 2021
I made a rookie plant collector mistake the other day, and failed to properly quarantine alocasia plants I found at The Home Depot. They were just too pretty to hide away! As a result, a handful of my plants started showing signs of spider mites and I had to act quickly before they got out of hand.
Truth be told, I can't tell for certain if the mites came home on the alocasia, as there are a million and one ways that the pests can make it inside, but my recent infestation did not start until I introduced the new plants.
Since they occur naturally outside, it is possible that one of my dogs picked some up and brought them in from the garden or a walk. I could have brushed up against an infested plant and brought them home on my jeans. They could have come in from any of the houseplants that I have started bringing inside now that night time temperatures are dipping.
Named for the silk webbing that they spin on the leaves of plants, spider mites are a royal pain. They can be found on a broad array of plants, including herbaceous ornamentals and woody plants, vegetable plants, fruit-bearing plants, and even various trees. They feed on plant leaves through their piercing-sucking mouthparts, sucking up all of the contents from individual plant cells.
When the cells are empty, they turn a silvery color, which is one of the most noticeable signs of a spider mite infestation. Delicate webbing, often on the underside of leaves, accompanied by small specks of white or red, are tell-tale signs of the little pests.
If you suspect that spider mites might be a problem, grab a plain white piece of paper, place it under a leaf, and shake the leaf. You'll notice small specks moving around if your plant does have spider mites, however, you may need to use glasses or another magnifying device to see them. If you observe webbing, or can see the mites on the plant, that is also plenty of confirmation of an infestation.
Now, spider mites do not mean that you need to toss your plants. There are many safe, effective ways to fight infestations if you are willing to put in the work. The first step for me, personally, is to quarantine and manually wipe off all the mites and webs that I can see with my strong-lense-prescription-assisted eyes, before spraying with a safe bug soap.
I used a mixture of water and Captain Jack's Dead Bug Brew that I sprayed, very liberally, on the leaves and stems. It should be noted that I did spray all of my plants outdoors. Captain Jack's is a personal favorite because it's main active ingredient is a natural bacteria, Spinosad, and it is safe around people and pets and can be used on plants you plan on eating produce from. Neem oil is an effective and safe insecticide, as well as most insecticidal soaps, just be sure to carefully read all of the instructions before use.
I was able to get the mites under control with a good spray down routine, but plants that have a large infestation may not be as lucky. Biological control measures, using predatory mites, are a great option for large infections. Most of the harmful mites in the area will either be two-spotted mites (Tetranychus urticae), and bean spider mites (T. ludeni). Predatory mites are incredibly effective on outdoor plants, and are safe to use on fruit and vegetable-bearing plants.
If you suspect that two-spotted mites are your problem, you can purchase a packet of Swirski mites. They work best in temperatures above 68-degrees, are incredibly aggressive, and can be used to treat an entire garden or single plant. Suggested application is 5-10 mites per square foot, or per individual plant. Swirski mites also feed on thrips and whiteflies, which are equally maddening to try and clean off of plants.
Californicus mites are another two-spotted mite predator, and work very well in cooler temperatures. Application suggestions range between one and five mites per square foot.
Chemical control is a last-resort option in spider mite control, because it takes a great deal of reading and requires a thorough understanding of everything on the label. Chemical labels are the law, and not following the instructions can result in making you, the plants, or surrounding life very ill. If mite infection is bad enough to use chemicals, it is best to call a professional.
Spider mites are a pesky pest. Learn from my mistakes and just quarantine the new plants, especially if they are purchased from a nursery that has both indoor and outdoor plants, for up to 30 days. Don't worry- masks aren't required after this kind of quarantine!