Spider Mites Can Be Awful to Get Rid Of. Here's How to Do It
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If you grow plants, you will probably encounter spider mites sooner or later. They can show up in your garden or on your houseplants to wreak havoc. These minuscule plant pests are extremely common—and particularly destructive if left unchecked.
Spider mites feed on hundreds of different plants, including vegetables, fruits, flowers, shrubs, trees, and houseplants. As the name indicates, they’re related to spiders and have eight legs and one body part.
“They’re tiny creatures that use their mouthparts to poke holes in the leaves and feed on the sap inside plants.” says Cory Tanner, extension horticulturalist at Clemson University. “They can be very difficult to eliminate, though you can manage the population if you catch them early.”
When spider mites feed on a plant, small patches of cells are killed, resulting in “stippling” or tiny yellowish dots on the leaf surface. “On heavily infested plants, the leaves becomes bronzed or bleached,” says David Oi, PhD, research entomologist with the USDA Agricultural Research Service. “Spider mites also may cause deformities on the bud and growing shoots, and the plants eventually may die.”
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These voracious pests, which are about the size of a period on the page, also reproduce quickly with eggs hatching in less than a week, if conditions are right, says Tanner. The population can explode—seemingly overnight—destroying garden or houseplants in a matter of weeks.
Read on to learn how to deal with these persistent little pests:
What Are Spider Mites?
There are many species of spider mites, but the ones that you’ll most commonly encounter are two-spotted spider mites (Tetranychus urticae), says Tanner. They get their name from two red spots, which you may be able to see with magnification, on their bodies.
Other common types include the spruce spider mite (Oligonychus ununguis), which feed on conifers, hemlocks, arborvitae, spruce, fir and junipers, and the southern red mite (Oligonychus ilicis), which attacks broadleaf evergreens such as Japanese holly, azaleas, and camellias.
Spider mites live in colonies. They have no wings, so they scramble from plant to plant or are transported by the wind. They survive winter as eggs or hidden in the soil or protected places under bark or garden debris. Outdoors, they have many natural predators, such as lady beetles and other types of mites, which usually keeps their populations in check, says Tanner.
How to Tell If You Have Spider Mites
The best defense is a good offense, so inspect the tops and bottoms of plant leaves regularly.
“You’ll usually notice the stippling or bronzing of the foliage first, or maybe the leaves just look a little ‘off,’” says Tanner. They eventually produce webbing on leaves to protect the mites and eggs. “By the time there’s webbing, you have a large population,” says Tanner.
Certain environmental conditions also make spider mites very happy.
“They prefer warm temperatures and low humidity levels, which is why they love it in your house in winter,” says Oi. They also tend to thrive when plants are drought-stressed or when conditions are dusty and dry in the garden.
How to Get Rid of Spider Mites
Unfortunately, there’s no easy solution! “The key is vigilance and persistence,” says Tanner. If you spot them, try these steps:
For garden plants, use the hose to blast mites off, hitting the tops and bottoms of leaf surfaces. Recheck every few days, and hose them off again. This works fairly well for small populations, especially if you’re tenacious.
If that isn’t successful, spray plants with insecticidal soap or horticultural oil. Read the label and make sure the product is okay to use on the type of plant you’re treating. These products work by smothering the bugs, so you must make contact in order to kill them, says Tanner. Because these sprays have little residual activity, you’ll need to re-treat every 5 to 7 days to deal with newly-hatched eggs or mites you missed.
Avoid using broad-spectrum pesticides such as permethrin and carbaryl, which have been shown to cause pesticide resistance and an increase in spider mite populations. Unfortunately, there are no systemic products available to homeowners for treating mites.
For houseplants, follow the same steps as above. You can spray them off with the hose or in the shower, if it’s too cold to take the plant outdoors, says Tanner.
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How to Prevent Spider Mites
Your best bet is to take an integrated approach which includes regular inspections, hosing off affected plants, and treating infected plants with insecticidal soap or horticultural oil, says Tanner.
Also, keep plants healthy by watering properly so they don’t become drought-stressed, says Oi. Running a small humidifier near houseplants to boost humidity levels also may help discourage a full-scale infestation because mites like it dry.
If bringing outdoor plants in for the winter, wash off them off with the hose first, then treat with insecticidal soap or horticultural oil as an extra step to prevent any hitchhikers from making it indoors, says Tanner. Regular rinses in the sink or shower once indoors also may help knock down any early infestations.
Finally, know when to call it quits. If you’ve tried all these steps and you’re still losing the battle, it may be easier (and less frustrating!) to pitch the infected plant and start over, says Tanner. This is especially important indoors because sacrificing an infected plant can protect the rest of your houseplant collection from eventually becoming infected.
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