Gnats, mealybugs and spider mites on houseplants

A new plant can bring pests home with it. Look over every part of a plant and its pot before you bring it in, and keep it apart from your other plants for one to two weeks so any pest has time to show.

What you need

• A magnifying glass and a sheet of white paper
• Cotton swabs and rubbing alcohol
• Yellow sticky traps
• Insecticidal soap labeled for houseplants

Steps

1. 1

   Isolate the plant

   Keep it away from your other plants until the pest is gone.

   2 min

2. 2

   Identify the pest

   Fungus gnats are small, dark flies with clear wings. Mealybugs are soft-bodied, about 3/16 inch long, and covered in white, powdery wax. Spider mites are about 1/50 inch long, so you'll usually need the magnifier. Tap a leaf over white paper and look for moving specks, fine webbing and a speckled look on the leaves.

   5 min

3. 3

   Wash the plant

   Wipe the leaves with a damp paper towel, changing towels often. Rinse a small plant in the sink and a large one in the shower. Wash your hands and tools afterward so you don't carry the pest to the next plant.

   10 min

4. 4

   Treat fungus gnats at the soil

   The larvae live in damp soil and feed on decaying roots and fungi, so gnats rarely harm the plant. Let the top of the soil dry as much as you can between waterings without letting the plant wilt. Yellow sticky traps catch some adults but won't solve it alone.

   3 min

5. 5

   Pick off mealybugs

   Use tweezers, or a cotton swab dipped in alcohol. Check along the veins under the leaves and where the leaves join the stems.

   10 min

6. 6

   Spray spider mites

   After washing, spray with insecticidal soap or a plant oil extract. Mites thrive in warm, dry air.

   5 min

7. 7

   Check again in a week

   Look over the leaves, stems and soil with the magnifier. No new specks, webbing or gnats means the plant can go back with the others.

   2 min

Signs to watch for

A shiny, sticky film on the leaves, or on the table under the pot, is honeydew. Mealybugs, scale and aphids leave it behind. Look closely at yellowing or discolored leaves too, and at the rims, edges and bottom of the pot and saucer.

When to let a plant go

A heavily infested, badly damaged plant can spread its pests to your other plants.

Using any product

Make sure the plant is listed on the label, and follow the label directions. A homemade soap mix can burn the leaves. Insecticidal soap labeled for houseplants is made for this. Water the soil a day or two before you spray, and never spray a plant that's dry and stressed. If a plant spends summer outdoors, skip imidacloprid, a systemic product that is toxic to bees.

If something goes wrong