Thrips: silvered leaves with black specks, and flecked flowers

Check your plant with the questions

Thrips are easier to recognize by their leftovers than by sight. A leaf they have fed on goes dull first, then develops a silvery or whitish sheen, usually across the top surface, and that pale area is sprinkled with tiny black spots like drops of dark varnish. The spots are droppings, and silvering paired with black specks points strongly to thrips.

The insects themselves

Adults are thin, narrow-bodied insects, under a tenth of an inch in length. They carry two pairs of slim wings edged with a fringe of hairs, folded back along the body when resting. Color varies with the species: most adults fall somewhere between pale yellowish and dark brown or near black. The young, called nymphs or larvae, lack wings and are paler, often creamy yellow.

Many kinds work out of sight, deep in flower buds, inside unopened shoot tips, or under the sepals, and they move off quickly when disturbed. On houseplants they use both faces of a leaf, with more of them underneath. Shake a leaf or flower over white paper and any thrips that fall show up as short slivers; a magnifying lens brings out the fringed wings. Sticky cards in bright yellow or blue, hung among the plants, catch the winged adults and give a rough count.

Kinds found on houseplants

• Banded palm thrips live on indoor plants year-round and prefer tough foliage: palms, citrus, ficus, monstera, dracaena and schefflera. Adults are a blackish brown, their wings banded in brown and white, and the leaves they attack silver over large areas.
• Western flower thrips go for leaves and blooms of many plants kept indoors or in a greenhouse, among them African violet, streptocarpus, gloxinia, cyclamen, fuchsia, pelargonium and impatiens. Plants stop growing well, petals become flecked, and flowers age early.
• Greenhouse thrips keep breeding all year in heated greenhouses. They silver upper leaf surfaces and mark them with small brown excrement spots. This species is sluggish, its adults seldom fly, and groups feed together under the leaves, so an infestation begins on one patch of a plant and widens slowly.

Not every thrips is a pest. Many feed mostly on pollen or fungal spores and do little harm, though pollen feeders can leave untidy pollen on orchid and African violet flowers and shorten how long they last. A few species hunt mites and small insects.

Damage that shows up late

Feeding in a bud or shoot tip only becomes obvious as the tissue expands. New leaves emerge curled, twisted or stunted, some turn papery and fall early, and petals open streaked or flecked where their pigment was killed before the bud opened. Badly attacked buds may stay shut. By then the culprits have often left, so find live insects before settling on thrips as the cause. Mites and certain true bugs stipple leaves in much the same fashion. The likeliest mix-up is spider mites, which leave silk webbing rather than black specks.

Silvered tissue stays silvered. A leaf that has lost its green does not get it back once the insects are gone, and no spray repairs it. The plant looks right again only after damaged leaves drop or are cut off and clean growth takes their place, so judge any treatment by the leaves and flowers that come next.

Two species, onion thrips and the western flower thrips, also spread plant viruses. The second carries tomato spotted wilt virus as well as impatiens necrotic spot virus, both capable of crippling or killing soft-stemmed ornamentals. Insecticides act too slowly to stop an infected thrips from passing a virus on, and a plant can be confirmed as infected only by a laboratory test.

A life cycle partly out of reach

Females insert their eggs into leaves, buds and other soft tissue, one or two a day and up to around a hundred in all. Two feeding nymph stages follow, then two stages that do not feed, known as prepupa and pupa, which many species spend in the potting mix or in sheltered corners of the plant. In warmth the whole cycle can take as little as two weeks; three to five weeks is more typical when conditions are good. Indoors and in a greenhouse they can breed through every season. Eggs inside tissue and resting stages in the mix are out of a spray's reach, which is one reason a single treatment seldom ends an infestation.

Getting on top of them

Cut off distorted shoot tips, flecked flowers and heavily silvered leaves and throw them away, because they carry insects as well as damage. Water evenly without overwatering, and go easy on nitrogen-rich fertilizer, since both overwatering and extra nitrogen are linked with bigger thrips populations. Picking or wiping them off achieves little; they move too fast.

Pyrethrins, neem oil, insecticidal soap and horticultural oil control thrips feeding in the open, greenhouse thrips in particular, but only where the spray lands. Drench shoot tips and buds, plus leaf undersides, and keep repeating while both thrips and tender growth are present. Thrips sheltering in curled leaves escape these sprays. These short-lived products also act on whitefly and aphids. Spinosad usually works better: it soaks a short way into the leaf, reaching thrips in protected spots, and stays active for a week or more. It harms bees and some beneficial insects for about a day after spraying, so keep it off plants in flower.

Some familiar products are poor choices. Imidacloprid commonly fails against thrips. Acephate, carbaryl, malathion and pyrethroids such as bifenthrin and permethrin do little to most thrips; by killing the predators that keep spider mites in check, they can bring on an outbreak of mites instead.

In a greenhouse, biological control is another route. Predatory Amblyseius mites, Orius laevigatus (a predatory bug), the rove beetle Atheta coriaria, and two nematodes, Steinernema carpocapsae and S. feltiae, are all sold against thrips. Most pesticides kill these helpers, so pick one approach or the other.

Keeping them out

Look over a new plant before buying it, flowers first, and leave behind any with pale flecks on the petals. Quarantine new arrivals away from other plants long enough for hidden insects to show. Clear away dead leaves and spent flowers, which can shelter thrips.

Plants whose sources name thrips

Each plant below is drawn automatically from records this site keeps, which list thrips as a pest wherever the RHS page or the NC State Extension page for that plant mentions them.

• African Spear NC State Extension
• African violet RHS
• Angel's Trumpet RHS
• Ara Banyan RHS
• Areca palm RHS
• Arrowhead plant NC State Extension
• Avocado RHS
• Bamboo Palm RHS
• Banana leaf fig NC State Extension
• Bearded iris RHS
• Begonia taliensis RHS
• Begonia venosa RHS
• Bengal Cardamom NC State Extension
• Blushing Philodendron NC State Extension
• Brazil Raintree RHS
• Calla lily RHS
• Canary Date Palm RHS
• Candy Leaf RHS
• Canterbury-Bell RHS
• Cape Primrose RHS
• Cast iron plant RHS
• Chamaedorea metallica RHS
• Chinese banyan RHS
• Chocolate Soldier RHS
• Christmas Orchid RHS
• Christmas Palm NC State Extension
• Cocktail Orchid NC State Extension
• Common fig RHS
• Creeping fig RHS
• Crimson Cattleya RHS
• Crucifix Orchid NC State Extension
• Delta Fig RHS
• Dracaena RHS
• Dracaena reflexa RHS
• Dwarf Palm RHS
• Dwarf umbrella tree NC State Extension
• Easter Cattleya RHS
• Easter lily RHS
• False Aralia RHS
• Fatsia RHS
• Ficus binnendykii RHS
• Fiddle-leaf fig RHS
• Fishtail Palm NC State Extension
• Flame Violet RHS
• Garden Croton NC State Extension
• Gardenia NC State Extension
• Gold Dust Dracaena RHS
• Green Zebra NC State Extension
• Hala NC State Extension
• Heartleaf philodendron NC State Extension
• Hoya NC State Extension
• Inch plant RHS
• Inch Plant RHS
• Indian Laurel RHS
• Iron Cross Begonia RHS
• Ivy Geranium RHS
• Kentia palm RHS
• Lacy tree philodendron NC State Extension
• Lady palm NC State Extension
• Lucky bamboo NC State Extension
• Madagascar dragon tree RHS
• Majestic Palm NC State Extension
• Mason's Congo Snake Plant NC State Extension
• Moses-in-the-Cradle RHS
• Moth orchid NC State Extension
• Parlor palm RHS
• Peepul Tree RHS
• Phalaenopsis schilleriana NC State Extension
• Polka dot begonia RHS
• Pothos NC State Extension
• Purple Heart RHS
• Pygmy date palm NC State Extension
• Rex begonia RHS
• Rubber plant RHS
• Schefflera RHS
• Silver Sword Philodendron NC State Extension
• Snake plant NC State Extension
• Tree Ivy NC State Extension
• Wax begonia RHS
• Weeping fig RHS
• Willow Leaf Fig NC State Extension
• Winterbourn Philodendron NC State Extension
• Zonal geranium RHS

Leaves speckled but webbed rather than spotted black belong on the spider mites page. For anything that fits neither, work through the diagnosis.

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