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Scale Insects

Scale Insects

Superfamily Coccoidea

Insectalso: Scale

Odd, stationary sap-suckers that look more like bumps, crusts, or specks on stems and leaves than insects. They cling in place under a waxy or shell-like cover, weakening woody plants, citrus, and houseplants, and the soft kinds drip sticky honeydew that grows black sooty mold.

🔎 How to spot it

Look for small, immobile bumps or flat scaly specks, often brown, gray, white, or black, stuck along stems, twigs, and leaf undersides; they do not look like typical insects and are easy to mistake for bark or disease. Armored scales sit under a hard cover that lifts off the insect, while soft scales are larger, rounder, and excrete honeydew. The only mobile stage is the tiny, newly hatched crawler.

🥀 Damage it causes

Scales suck sap, and heavy infestations yellow leaves, stunt growth, cause dieback of twigs and branches, and can kill a stressed plant over time. Soft scales coat the plant and everything below it in sticky honeydew that turns black with sooty mold, fouling leaves and fruit. Citrus, fruit trees, woody shrubs, and houseplants are common hosts.

🛡️ Prevent it

Inspect new plants and prune out and destroy heavily encrusted twigs and branches before scales spread. Keep plants healthy and unstressed, since vigorous plants tolerate scale better, and avoid the excess nitrogen and dust that favor outbreaks. Protect and encourage the lady beetles and parasitic wasps that are the main natural controls by avoiding broad-spectrum insecticides, which trigger scale flare-ups.

🧯 If it is already here

For light infestations, scrub scales off with a soft brush or dab them with a cotton swab, or prune out infested wood. The standard control is horticultural oil, which smothers scales and their eggs: spray thoroughly to coat stems and leaf undersides, timed to the spring crawler stage and repeated, with a dormant-oil application on deciduous trees in winter. Control the ants that protect soft scales for their honeydew.

💡 Good to know

Timing is everything: scales are nearly immune to sprays under their covers, so target the brief crawler stage in late spring (a piece of sticky tape on a twig shows when crawlers are out). Their many natural enemies usually keep scale in check, and most flare-ups follow the loss of those beneficials to broad-spectrum insecticides or to ant tending.

🌱 Plants it attacks

714 plants in the library can be attacked by this pest

Acorn SquashAdirondack Blue PotatoAdzuki BeanAfrican Blue BasilAfrican MarigoldAgapanthusAgeratumAgrimonyAji Amarillo Pepper🍓Albion StrawberryAlice du Pont Mandevilla🥔All Blue PotatoAlmondAloe VeraAmbrosia CornAmerican BasswoodAmerican Beauty Dragon FruitAmerican BeechAmerican PersimmonAmethyst Falls WisteriaAmish Paste TomatoAnaheim PepperAnemoneAngelique TulipAngeloniaAniseAnise HyssopAnjou PearAnnabelle Smooth HydrangeaAnnual VincaApeldoorn TulipApple MintApril Tryst CamelliaArbequina OliveArizona Sun Blanket FlowerArkin CarambolaArmenian CucumberAroniaArp RosemaryArugulaAshwagandhaAsian PearAsian PersimmonAtemoyaAtlantic Giant Pumpkin🥕Atomic Red CarrotAucubaAugust Beauty GardeniaAunt Molly's Ground CherryAutumn Joy SedumAvocadoBachelor's ButtonBalsam FirBalsam PoplarBanana PepperBarbara Karst BougainvilleaBartlett PearBay LaurelBayberryBeach PlumBeauregard Sweet PotatoBecky Shasta DaisyBee Balm🍅Beefmaster TomatoBenarys Giant ZinniaBengal Tiger CannaBetter Boy Tomato🥬Bibb Lettuce🍅Big Beef TomatoBig Boy TomatoBilberryBing CherryBitter MelonBlack BeanBlack Beauty EggplantBlack Beauty ZucchiniBlack Beluga LentilBlack Cherry TomatoBlack CrowberryBlack Currant🍉Black Diamond WatermelonBlack Kabouli ChickpeaBlack Krim TomatoBlack RaspberryBlack Sapote🥬Black Seeded Simpson Lettuce🥕Black Spanish RadishBlack Tartarian CherryBlack WalnutBlack-Eyed PeaBlack-eyed Susan VineBlood OrangeBloomsdale SpinachBlue Bird DelphiniumBlue Bird Rose of SharonBlue FescueBlue Lake Green BeanBluecrop BlueberryBocking 14 ComfreyBok Choy

For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.