Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
See that web on the underside of that leaf? It wasn’t made by a spider. It was made by its cousin, the spider mite who got its name because it spins webs just like spiders.
What are Spider Mites?
Spider mites are not insects. They are spiders. You can tell by counting their legs. They have 8 legs like spiders instead of 6 legs which is characteristic of all insects. You’ll need a 10x magnifying lens to count the legs. Spider mites are tiny, only 1mm or 4/100ths of an inch in size and come in various colors. The easiest way to ID them is to place a sheet of paper under a leaf and shake the leaf. The tiny black dots that fall on the paper are the mites. It’s easier to see them on the paper with your magnifying lens than on the back of a leaf where they live.
Spider mites live fast and die young. They hatch within 3 days and mature within 5 days. Females can lay up to 20 eggs per day. During their brief lifetime of only 2 to 4 weeks, they can lay hundreds of eggs. This quick life cycle allows them to easily become resistant to chemical pesticides.
Spider mites live on the undersides of leaves. They have a varied diet, enjoying plants like tomatoes, peppers, potatoes, strawberries, corn and beans. They spin their characteristic webs to protect their colonies, especially their vulnerable eggs, from predators. Since the mites themselves are so tiny, their webs are usually the first sign you will see indicating their presence.
You may also notice that the leaves on your plants have developed yellow spots, have begun to curl or die and drop off of the plants. Spider mites feed by literally sucking the life out of your plants. They pierce the leaves and feed on the sap inside them.
Knock Them Off With a Hose
The best way to get rid of spider mites is with a hose. Attach a nozzle that will give you a strong spray and spray your plants, especially the undersides of the leaves. This knocks the mites off the leaves. You can do something similar for your houseplants. Turn them upside down in a sink and using the sprayer attachment, wash the leaves thoroughly. Alternatively, you can use a sponge to clean each individual leaf.
Use Neem Oil
Another tried and true method is to spray your plants with neem oil. It acts in different ways. It acts as a repellent preventing the mites from infesting your plants. It can interfere with their ability to feed. Neem can also interfere with their hormones making it difficult for them to lay eggs. You will need to spray for a couple of weeks, concentrating on the undersides of the leaves, to completely rid your plants of spider mites.
Use Insecticidal Soaps
Insecticidal soaps are an ecologically friendly way to get rid of spider mites and insects that damage your plants. They work by smothering the pests. Just as soap can dry out your skin, insecticidal soap dries out the insects’ bodies, killing them. Like the neem oil, you will need to spray for a couple of weeks to make sure that you have gotten rid of all the adults and eggs.
Use Beneficial Insects
Not all mites are bad. The predatory mite eats spider mites for breakfast. And lunch. And dinner. They love adults, juveniles, even eggs. They will happily eat up to 5 adults or juveniles each day or 20 eggs per day. You can purchase them for release in your garden. As with all predatory insects, don’t expect them to stick around forever. Once they have eaten all of the spider mites, they will move on in search of more food.
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Keep the Soil Moist
Spider mites thrive in hot, dry conditions. Keep your plants well-watered. The humidity from the moist soil will discourage the mites from moving in. If you allow your plants to become dry, especially in hot summer conditions, spider mites will make themselves at home.
Remove Infested Leaves and Plants
A good way to stop an infestation of spider mites is by throwing them away. The minute you see an infected leaf, remove and discard it in the garbage, not your composter, before the mites move on to the other leaves on the plant. If an entire plant is infested, dig it up, wrap it up and throw it in the garbage before it can infect your other plants.
Check Plants For Spider Mites Before Purchasing
You know that old saying about an ounce of prevention. When you are purchasing plants, examine them closely. If they show any signs of infestation, don’t buy those plants. Once you purchase your plants and bring them home, even if they seem perfectly healthy, isolate them from your other plants for at least a week to make sure that they aren’t harboring any unwelcome visitors.
Spider mites are tiny terrors. They reproduce quickly and suck the life out of your plants. Fortunately, getting rid of them is not difficult.
Questions & Answers
Question: If you spray them with Dawn soap diluted by water, will this mixture kill the plants?
Answer: Soap is will not harm plants, only the insects on the plants. This includes beneficial insects such as pollinators which you want on your plants so be careful where you spray your soapy mixture. Make sure that you are only spraying it on the pests that you want to kill.
Question: After getting rid of a plant, can I repurpose the dirt in the pot?
Answer: It is never a good idea to reuse potting soil. After getting rid of the plant, you should also throw out the soil, then clean and disinfect the pot before using it again.
Question: In the UK we are very lucky to have a viable, natural, alternative method for getting rid of spider mites. Do you not have this in the U.S. yet?
Answer: Actually, we do. Here in the U.S., you can order predatory mites to eat the spider mites that are infesting your plants.
Question: How does Dawn soap kill spider mites?
Answer: Soap kills spider mites by drying them out. Just as soap can dry out your hands, it also dries out insects that will kill them.
© 2018 Caren White
Caren White (author) on July 03, 2020:
Actually there are two reasons that the hose method works well. The first one is the obvious one that it knocks the spider mites off of your plants. The second was noted in my article: "Spider mites thrive in hot, dry conditions. Keep your plants well-watered. The humidity from the moist soil will discourage the mites from moving in. " So when you spray, you are creating a humid environment that drives them away from both the plant that you are spraying as well as the rest of your plants.
Elise Mazzoni on July 02, 2020:
Thanks for the info! Quick question, if I am spraying water to dislodge them, will they not just move to another plant? Shouldn’t I be killing them too? Or does the water somehow do that?
Caren White (author) on June 24, 2020:
The advice to remove aphid infested plants really only applies to smaller plants such as your veronica and phlox, not something as large as a climbing rose. Remove the most heavily infested canes plus any other infested plants in your garden and continue spraying daily. Rather than using Neem oil only, I would additionally use water from a garden hose sprayed hard enough to knock the aphids off the rose. Good luck! I hope that you are able to save your rose.
Caryn Wagner on June 23, 2020:
I took too long before realizing that my climbing rose was infested with spider mites since I had only had issued with them on dahlias, a type of Veronica and phlox in my garden. The rose is putting out a beautiful new shoot , and I’m prepared to remove most of it to get it back to health, but it seems you are suggesting that I take it out completely. I have been using Eight and neem oil alternately, and I’d love to save the rose, but I’ll wait for your direction. Thank you so much.
Caren White (author) on June 23, 2020:
At this point, it sounds like it is too late. The infestation is too great. Your best bet is to discard your rosemary and start over. To effectively rid plants of spider mites, you need to spray daily with Neem, insecticidal soap or water. Spraying weekly is not enough because of the spider mites' very short life cycle. You need to spray more frequently.
Christian on June 22, 2020:
I’ve been treating my rosemary bushes weekly with neem oil and half way through the week spraying off the mites with a strong hose. Is this treatment often enough? The infestation seems to get worse every week and we are desperate to relieve our rosemary from the reign of the spider mites!
Caren White (author) on August 25, 2018:
It depends on the species. Not all spiders are dangerous to humans.
Caren White (author) on March 12, 2018:
Thanks, Jo! Happy that you found it useful.
Jo Miller from Tennessee on March 12, 2018:
Great advice for gardeners. Thanks for the info.
Caren White (author) on March 05, 2018:
Peggy, I'm glad to hear those methods work for you. Thanks for reading and commenting.
Peggy Woods from Houston, Texas on March 05, 2018:
The advice you gave is exactly what I have tried in our garden. I use water spray from the hose and have also used soapy water on them. Fortunately we don't have to battle them that often.