Plant Problem Diagnosis Key / Pests
Scale insects
Coccidae, Diaspididae
Insects that settle permanently under a waxy or hard cover and feed on sap. The young crawlers move the most and are the stage most treatments reach.
Signs
- Small bumps or shells along stems and leaf veins.
- Sticky leaves and sooty mold below (soft scales).
- Yellowing, dieback and thin growth on heavily covered branches.
What favors it
New plants that bring them in; outdoors, natural enemies usually keep them down later in the season.
Prevention
- Apply dormant oil before bud break on trees and shrubs.
- Inspect stems and leaf veins of new plants.
- Scrub light infestations off branches with a soft plastic brush.
Crops it shows up on
Apple, pear & stone fruit; Roses & ornamentals; Houseplants; Shade & ornamental trees; Evergreens & conifers (pine, spruce, juniper).
Often confused with
Sources
- Scale insects on Minnesota trees and shrubsUniversity of Minnesota Extension
- Oystershell ScaleMontana State University Extension
- Scale Insects on Indoor PlantsUniversity of Maryland Extension
Treatment by crop
Cultural, biological and chemical options in the order to use them, and notes written for each crop.
Identification is free. Treatment is on the Home and Pro plans.
Questions in the key that lead here
- Look the plant over, leaf undersides included. Are insects, mites, slugs, eggs, webbing or droppings on it?
Yes, something living or its traces - What is on the plant?
Bumps or cottony tufts stuck to stems and leaves - What are the bumps like?
Hard or waxy shells
Not a match? Start the key or describe what you see.
More photos
More from university Extension: search Extension pages on scale insects, or find a plant diagnostic lab through your state's Extension.
Other pests
- Aphids
- Bagworms
- Bark beetles of pine and spruce
- Broad mites and cyclamen mites
- Caterpillars
- Cicada and twig-cutting damage
- Colorado potato beetle
- Cucumber beetles
- Cutworms
- Elm leaf beetle
- Emerald ash borer
- Flea beetles
- Fungus gnats
- Galls on leaves and twigs
- Hemlock woolly adelgid
- Japanese beetles
- Lace bugs
- Leafminers
- Mealybugs
- Pine sawflies
- Root aphids
- Root-knot nematodes
- Russet mites
- Sapsucker damage
- Shore flies
- Slugs and snails
- Spider mites
- Spongy moth (gypsy moth)
- Spotted lanternfly
- Squash bugs and stink bugs
- Squash vine borer
- Tent caterpillars and fall webworm
- Thrips
- Whiteflies
- Wood borers