Plant care guide

Calathea Thrips: Where They Hide and How to Treat Them Safely

Updated

Why does my Calathea have thrips?

Thrips on a calathea leave dull, silvery or pale-streaked patches and tiny dark, varnish-like droppings, mostly on leaf undersides. They hide in rolled new leaves and in the sheathing leaf bases, and their pupae can sit in the potting mix.

What to do first

Isolate the plant, rinse both leaf surfaces, look into rolled new leaves, and replace the top of the potting mix or repot. If thrips persist, use insecticidal soap or oil labelled for houseplants, tested on one leaf first, and repeat.

Thrips on a calathea are hard to see and slow to clear, which makes them stressful. They can be beaten with patience and repeat checks. The key on this plant is knowing where to look and how gently to treat.

Most plants sold as calathea are now Goeppertia. University of Maryland Extension’s thrips page says thrips feed on a wide variety of indoor plants. It warns they reproduce rapidly and readily become resistant to insecticides.

Confirm It Is Thrips

Maryland describes thrips as rice-shaped insects 1–2 mm (about 1/16 in) long, yellow, brownish or glossy black. Juveniles are wingless and often near-white or yellow.

Signs on a calathea:

  • Dull or silvery patches. The RHS indoor sap-feeders page says leaves become increasingly dull or silvery. On patterned leaves, compare with an untouched leaf of the same age.
  • Pale flecks in rows. Maryland says rows of stippling can merge into pale or silvery streaks.
  • Dark droppings. The RHS likens thrips excrement to small dollops of dark varnish.
  • Crinkled new leaves. Maryland says leaves that are still expanding when thrips feed can become permanently stunted, crinkled or curled.

Test it. UC IPM’s thrips notes suggest shaking foliage over white paper and hanging blue or yellow sticky traps. Spider mites cause similar stippling but leave fine webbing; see our calathea curling leaves guide if you find neither.

Where Thrips Hide on a Calathea

The RHS says thrips are found on both leaf sides but are generally more numerous underneath. Maryland lists young leaves, leaf margins, the main vein and the nooks where leaf stalks join the stem.

On a calathea, that means:

  1. Rolled new leaves. NC State Extension says new G. makoyana leaves grow rolled up. Shine a torch into the scroll.
  2. Leaf bases. NC State describes the petioles as sheathing at the base. Check where the stalks wrap each other at soil level.
  3. The midrib underside, especially on the purple undersides where dark droppings are harder to see.
  4. The potting mix. UC IPM says pupae often drop to the soil or leaf litter.

Treat a Thin, Sensitive Leaf

NC State describes G. makoyana leaves as papery thin. Treat in steps and check the plant between them.

  1. Isolate the plant. Clemson Extension’s houseplant pests factsheet advises isolating new plants for six weeks; treat an infested one the same way.
  2. Rinse both sides of every leaf. UC IPM’s houseplant problems page suggests washing thrips off with water. Support each leaf under a lukewarm shower, and let foliage dry afterwards.
  3. Trim the worst leaves. Maryland suggests removing disfigured leaves with thrips tucked inside.
  4. Replace the mix. Maryland says repotting into fresh mix may remove pupae in the soil. It adds that mixes high in organic matter may favour thrips.
  5. Use soap or oil if they return. Maryland lists horticultural oil and insecticidal soap as low-toxicity choices. Sprays must contact the thrips, and repeat applications are needed.

Spray safely on this plant:

  • Spot-test. UConn’s insecticidal soap factsheet says to wait at least 24 hours for spotting, burned tips or scorch. It lists soft new growth among the higher-risk tissue.
  • Use soft water. UConn warns soap in hard water may be less effective and more toxic to plants.
  • Avoid home remedies. Maryland advises against household soap or detergent sprays.

UC IPM calls spinosad generally more effective than soaps and oils for thrips. Clemson also lists spinosad. Follow the label for indoor use.

Prevention and When to Stop

Maryland says high humidity may discourage most thrips species indoors. That suits a calathea. It also advises against excess nitrogen, which produces tender growth thrips prefer.

Keep a blue sticky card near the plant and check new leaves weekly, as UC IPM advises for new plants. Damaged silvering will not turn green again, so judge success by clean new leaves.

Maryland notes that heavily infested indoor plants are often best discarded. Our thrips guide and pest treatment guide cover the full treatment ladder. The calathea hub lists our other guides.

Other calathea problems we cover: drooping, water quality sensitivity, leaf movement, sunburn treatment, root rot.

References

How this guide was put together: University of Maryland Extension, UC IPM, RHS, Clemson Cooperative Extension, NC State Extension and UConn guidance.

Other Calathea problems

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Knowledge record: pg-calathea--thrips