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Spider Mites

Garden pest · Tetranychidae

Description​

Spider mites are tiny, plant-feeding arachnids in the family Tetranychidae, not insects. Several species attack garden and houseplants; the two-spotted spider mite is especially common. They usually live on the undersides of leaves, where they pierce plant cells and feed on their contents. Early damage appears as scattered pale dots. As feeding continues, leaves may look yellow or bronze, dry out, and fall. Heavy infestations can slow growth and cover leaves and stems with fine silk webbing. Spider mites reproduce quickly, particularly during hot, dry weather, so a small population can become conspicuous within weeks. They affect vegetables, ornamentals, fruit crops, and indoor plants. Wind, clothing, tools, and newly acquired plants can help them spread. Although healthy plants can tolerate a little feeding, prolonged infestations reduce vigor and may seriously damage seedlings or plants already stressed by heat or drought.

Symptoms​

  • Pale speckles or stippling
  • Yellowing leaves
  • Brown or crispy leaf edges
  • Fine webbing
  • Leaves dropping
  • Stunted growth
  • Insects visible on the plant

How to Identify​

Inspect the undersides of affected leaves with a hand lens. Spider mites look like tiny moving dots, often with eggs and shed skins nearby; adults have eight legs. Tap a leaf over white paper to make moving mites easier to see. Look for fine, pale stippling that progresses to yellowing or bronzing, and, in heavier infestations, delicate webbing around leaves or stems. Dust or nutrient problems can also discolor leaves, but they do not produce moving mites or silk. Spider webs made by ordinary spiders tend to have coarser strands and are not accompanied by widespread feeding speckles. Check several leaves: early infestations may have no visible webbing.

Prevention​

Inspect new plants, especially leaf undersides, before bringing them into the garden or home. Keep new houseplants apart from established ones briefly so emerging problems are easier to spot. Check susceptible plants regularly during hot, dry periods; finding mites before webbing develops makes control easier. Water plants according to their needs, since drought stress makes mite damage more severe. Avoid excessive nitrogen fertilizer, which can encourage tender growth attractive to mites. Where practical, rinse dusty foliage and maintain suitable humidity and airflow without keeping leaves constantly wet. Avoid unnecessary broad-spectrum insecticides: they can kill predatory mites and other natural enemies, allowing spider mites to rebound. Remove heavily infested weeds and spent plant material, and clean up infestations before moving plants close together.

Treatment​

Start by isolating affected potted plants and spraying leaf undersides with a firm stream of water to dislodge mites. Repeat every few days, checking that the plant can tolerate the spray. Remove and bag badly infested leaves, but do not strip a plant of most of its foliage. For persistent infestations, thoroughly coat leaf undersides with an insecticidal soap or horticultural oil labeled for the plant and site. Test a small area first, follow the label, and avoid application during high heat, strong sun, or drought stress. Repeat as directed because eggs and newly hatched mites can survive an initial treatment. Predatory mites can be effective, particularly in greenhouses and indoor growing spaces, if conditions suit the species used and incompatible pesticides are avoided. If damage remains severe, consider a miticide specifically labeled for spider mites and the affected plant; follow all directions and rotate labeled modes of action to limit resistance.

Plants Affected​

Abelia, Amaryllis, American Basswood, Anthurium, Arborvitae, Arrowroot, Bald Cypress, Banyan, Bay Leaf, Bell Pepper, Bird of Paradise, Bougainvillea, Burning Bush, Butterfly Bush, Cedar, Chrysanthemum, Cork Arborvitae, Cork Bristlecone Pine, Cork Fir, Cork Hemlock, Cork Juniper, Cork Spruce, Corpse Flower, Cosmos, Cotoneaster, Cranberry Bean, Crown of Thorns, Curry Leaf, Cypress, Date Palm, Desert Rose, Douglas Fir, Edamame, Eggplant, Euonymus, Fir, Frangipani, Freesia, Galangal, Gardenia, Geranium, Gerbera Daisy, Heliconia, Hemlock, Hibiscus, Honey Locust, Hyacinth Bean, Impatiens, Indian Rubber Tree, Jade Vine, Jasmine, Jicama, Juniper, Kadupul Flower, Lemongrass, Lima Bean, Littleleaf Linden, Locust, Marigold, Marjoram, Milkweed, Mint, Morning Glory, Myrtle, Oleander, Orchid, Orchid Cactus, Oregano, Palm, Passionflower, Plumeria, Potentilla, Rose of Sharon, Rosemary, Sacred Fig, Sage, Savory, Soybean, Spirea, Spruce, Thuja, Thyme, Ulex, Weeping Fig, Weigela, Xylosma, Yardlong Bean, Yew, Yucca, Zinnia

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