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Kinzler: Prescription for keeping houseplants insect-free

Gardening columnist Don Kinzler offers tips for inspecting houseplants, a list of the most common houseplant insects and how to get rid of them.

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Early plant detection is a key to houseplant insect control.
David Samson/The Forum
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If houseplants generated electricity, would we call them power plants?

Even without electricity, houseplants are a hot gardening activity. Houseplant care bridges nearly all demographics, because we can grow them whether we’re young, old, rural, urban, apartment dweller or homeowner.

Humans aren’t the only ones enjoying the current upswing in houseplant popularity. Insects are always looking for a free meal, and it’s amazingly easy for pests to take up residence on our plants.

Following are guidelines for keeping houseplants insect-free.

  • Insect populations tend to balloon rapidly if we’re not observant, and early detection is key to controlling small outbreaks before they explode.
  • Isolate new plants for one to two weeks, giving any pests time to become more visible.
  • A good opportunity to look closely at plants is while watering.
  • A ten-power hand magnifying lens is helpful when looking for insects, because many are small and easily go undetected.
  • Inspect tops and undersides of leaves for insects themselves, or webbing, holes or eggs.
  • Watch for honeydew—a shiny, sticky substance made by aphids, mealybugs and scale insects—as they suck plant sap. Honeydew can be seen glistening on the upper surface of leaves, and on tabletops or floors, and is good indication insects are present.
  • Some insects like fungus gnats and whiteflies will move when disturbed at watering time.
  • Yellow sticky traps located near plants can detect presence of flying insects.
  • Examine leaves that are discolored, as this may be evidence of a pest problem.
  • Keep soil surface free of dead leaves, stems and flowers, which can harbor insects.
  • Never pot indoor plants using soil from the garden or flowerbeds. Use new, sterile, high-quality potting mix.
    More on houseplants
    The store, owned by brothers Casey and Kale McCollum, features over 4,000 houseplants, pottery, soil, plant care products and more.
  • Many insect problems can be managed without chemicals if caught early. Wiping leaves with a damp paper towel, changed frequently, cleans leaves and can dislodge insects. Washing leaves by spraying gently in the kitchen sink removes many small insects.
  • If insects are limited to a few leaves or stems, simply remove the plant parts and dispose.
  • In severe infestations, cutting the plant back can help eliminate pests, or make it easier to treat the remaining parts.
  • If a plant is heavily infested with insects, it might be wise to enclose the entire plant in a plastic bag and dispose, before the problem spreads to other plants.

Common houseplant insects

  • Mealybugs attach themselves to leaves or stems and cover themselves with a white cottony material.
  • Fungus gnats are small black flies that lay eggs in soil that hatch into larvae that morph into more adult flies, that lay more eggs, creating a continuous cycle of life.
  • Spider mites are barely visible until damage is evident. Watch for speckled discoloration on leaves, and severely infested leaves look bleached or pale green. Fine webbing is visible when populations explode.
  • Aphids have small, pear-shaped bodies, and can be green, whitish, red, green or brown. They often cluster on stem tips or leaf undersides.
  • Whiteflies cling to leaf undersides and flutter up when disturbed.
  • Scales are covered with a waxy shell-like covering, attach themselves to stems or leaves, barely move, and are brown, gray or white.
102222.F.FF.GrowingTogether
Garden cenyters sell many products for houseplant insects including systemic granules.
David Samson/The Forum

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Insecticidal products

  • Insecticidal soap is effective against scales, aphids, whiteflies and spider mites. It has no residual activity and must directly saturate insects to kill them. Homemade soap mixes aren’t advised, because they can burn some houseplants.
  • Neem oil disrupts insect growth and is effective against whiteflies and aphids.
  • Mosquito Bits is labeled for fungus gnat control, and when applied to the soil, breaks the life cycle of gnats by killing their larvae, eventually resulting in no more adult flies.
  • Systemic houseplant insecticides are applied to the soil, taken up by the roots, and protect plants internally for months as insects suck sap. Effective against mealybugs, scales, aphids, whiteflies and spider mites.
  • There are many brands of houseplant insect sprays available. If applying indoors, to avoid human exposure enclose the plant in a plastic bag and seal shut. Cut a small hole in the bag and insert the spray nozzle. Move the nozzle around to spray the plant’s upper and lower leaf surfaces, then quickly cover the hole with tape.
More gardening columns from Don Kinzler

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.
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