Spider Mite Control: How to Spot and Stop Spider Mites on Plants

Your beans, tomatoes, marigolds or houseplant leaves have gone dull and speckled, and up close you can see fine silk strands across the leaf undersides. That pattern usually means spider mites. They are hard to see, they multiply fast in hot weather, and the wrong spray can make them worse. This guide shows you how to confirm them, change the conditions that favor them, and pick controls that work.

How to identify spider mites

Spider mites are not insects. They are tiny relatives of spiders, with eight legs and an oval body. Adults are under 1/20 inch long, so without magnification they look like moving dots. A 10x hand lens makes them easy to see.

The two-spotted spider mite is the one most gardeners meet. Adults are pale yellow-green to greenish, with two dark spots on the body once they have been feeding. Other species are red, brown or orange. You do not need to know the exact species to manage them.

The white paper test. Hold a sheet of white paper under a leaf with suspected damage and tap the leaf sharply. Wait a few seconds. Specks that start walking around are mites. Specks that stay still are probably dust.

If you find visible clusters and sticky leaves rather than webbing, read the aphid control guide.

Signs of spider mites

• Stippling. Mites suck out the contents of leaf cells, leaving tiny pale dots. Many dots together look like a sandblasted or faded patch.
• Bronzing and color change. Heavily fed leaves turn bronze, yellow or reddish and may drop.
• Webbing. High populations spin silk over leaf undersides, between leaves and stems, and over fruit. Webbing is the easiest way to tell mites from aphids and thrips.
• Specks on the underside. Colonies live mostly on leaf undersides. Look for the mites, their tiny round eggs and empty egg shells left after hatching.

Damage often shows up after the mites have peaked. Do the paper test before you treat: if no live mites drop, the outbreak may already be over, and plants often recover.

Why spider mites show up

• Hot, dry weather. Mites feed and reproduce faster when humidity is low. Outbreaks are common in mid to late summer.
• Dust. Plants along dirt roads, driveways and dusty paths get worse outbreaks. Dust on leaves also interferes with the predators that eat mites.
• Drought stress. Water-stressed plants tolerate mite feeding poorly and may be more nutritious to mites.
• Excess nitrogen. High nitrogen in foliage speeds up mite reproduction.
• Pesticides that kill predators. Carbaryl, some organophosphates such as malathion, and some pyrethroids kill the natural enemies of mites. Some of these can also spur mite reproduction. Outbreaks after these sprays are worst in hot weather.

How to get rid of spider mites, step by step

This follows the integrated pest management order: fix conditions first, spray last.

1. Confirm and check often. Use the paper test or a hand lens on leaf undersides weekly during hot weather, more often on plants that had mites before.
2. Water well. Keep plants evenly watered during hot, dry spells to reduce drought stress.
3. Hose them off. A forceful water spray aimed at leaf undersides knocks off and kills many mites, breaks up webbing and rinses away dust. Repeat every few days during an outbreak. This works on garden plants, shrubs and small trees.
4. Cut down dust. Wet down or mulch dusty paths and bare ground near affected plants.
5. Prune and remove. Clip and bag the most heavily infested leaves or shoots. Pull out spent annuals and vegetables that are covered in webbing rather than trying to save them.
6. Protect predators. Predatory mites, small, dark lady beetles called spider mite destroyers, minute pirate bugs, lacewings and predatory thrips all eat spider mites. Avoid the insecticides listed above. You can buy predatory mites, but they need prey and fairly humid conditions to establish, and results outdoors are mixed. They have a better record on indoor plants.
7. Spray oil or soap if you still need to. See the next section.

Do not spray a broad-spectrum insecticide to “clean up” mites. Carbaryl and many pyrethroids kill the predators that hold mites down, and the mites can bounce back in larger numbers within a couple of weeks.

Oils, soaps and miticides

Horticultural oil is one of the more effective mite sprays available to homeowners. Insecticidal soap also kills mites on contact, but results on two-spotted spider mites are less consistent. With both:

• They only kill mites they touch, so soak the leaf undersides.
• They do not keep working once dry, so plan on repeat applications while live mites remain.
• Do not spray water-stressed plants or when temperatures are above about 90°F. Test a few leaves first on sensitive plants.
• Do not apply sulfur within about 30 days of an oil spray, and do not use sulfur in hot weather. Together they can burn plants.
• Read and follow the label for the plants and crops it allows.

Miticides (also called acaricides) are products made to kill mites. Spider mites develop resistance quickly, and cross-resistance is common among products that share a mode of action. To slow that down:

• Check the mode of action group number on the label.
• Do not apply products from the same group back to back against the same generation of mites.
• Most miticides do not kill eggs, so a follow-up application, often 10 to 14 days later, is usually needed. The label sets the interval.
• Read and follow the label, which overrides any general advice, including limits on the number of applications per season.

Before buying any product, review using pesticides safely.

Spider mites on vegetable crops and onions

If you grow onions, beans, melons, squash or other vegetables on a larger scale, the same principles apply, with a few points that matter more in the field:

• Two-spotted spider mites attack onions. Look for fine stippling that turns into bronzed and browning leaves, plus webbing. Mites overwinter in crop debris and weeds, and they can go through many generations in one season.
• Avoid flaring mites with other sprays. Broad-spectrum insecticides, including malathion and pyrethroids used against other crop pests, can kill mite predators and stimulate mite reproduction. Choose selective products for other pests where you can.
• Manage water and nitrogen. Keep plants out of drought stress and use slow-release nitrogen rather than heavy doses.
• Clean up weeds and crop residue at field edges, where mites survive between seasons.
• Know the other onion mite. Bulb mites are creamy white and feed below ground on roots, the basal plate and bulb skins, opening the door to rots. Let crop residue break down before planting, use clean sets and transplants, rotate away from onions, and store bulbs cool and dry.
• Rotate miticide groups and keep records. For commercial crops, follow your state extension vegetable guide and the product label for the crop, rate and preharvest interval.

Spider mites on houseplants

Indoors there are few natural enemies to help, so soap and horticultural oil do most of the work. Treat every susceptible plant at once. Rinse small plants in the shower or wipe larger leaves, trim and bag heavily infested growth, and isolate infested plants. Horticultural oil or insecticidal soap labeled for indoor plants can follow, repeated every 1 to 2 weeks while mites persist.

When to call a professional

Most garden mite problems respond to water, dust control and patience. Bring in help if:

• Mites keep returning on large trees or shrubs you cannot reach with a hose.
• You manage a commercial crop and need help with thresholds, resistance and miticide rotation. Your county extension office is the place to start.
• You are unsure whether you have mites or a plant disease. Your county extension office can help with diagnosis.

Spider mite questions

Why did mites get worse after I sprayed? If you used carbaryl, malathion or a pyrethroid, you likely killed the predators that were keeping mites in check. Some of these products also spur mite reproduction, especially in hot weather.

How fast do they multiply? Very fast. In warm weather with plenty of food, a generation can go from egg to egg-laying adult in under a week.

Will my plant recover? Often, yes. If the paper test shows few live mites and new growth looks clean, keep the plant watered and leave it alone.