Scale

Bumps that never move?

Tiny shells drinking your plant. Meet what eats them.

Check that it's scale

Is it scale?

Scale gives itself away three ways.

1

Shells along the stems.

Small shells or domes, lined up along stems and leaf veins.

Leaves blackened with sooty mold over scale honeydew

2

Sticky leaves, or black mold.

Soft scale drips honeydew, and sooty mold grows on it.

Tiny yellow-orange scale crawlers on a stem

3

Tiny moving crawlers.

Yellow to orange young. The sign scale is still active.

Not quite matching?

Bumps, but not scale?

Mealybugs

White, fuzzy and cottony, tucked into the leaf joints.

How to treat mealybugs

Whitefly young

Flat pale ovals under the leaves, with white fliers nearby.

How to treat whiteflies

Aphids

Soft-bodied clusters that walk, mostly on new growth.

How to treat aphids

Scale it is. Meet them ↓

Which scale?

Hard or soft. Your fingernail decides.

Armored scale

Flat and hard. The cover pops off dry and the body stays behind. No honeydew.

Soft scale

Larger and rounded. Squashes wet and leaves the plant sticky.

Karen's noteKaren Horn, owner

Wash your hands either way.

Meet the scale

A sap-drinker under a shell.

No obvious head, and no rush.

Scale are sucking insects related to mealybugs and aphids. Each one lives under a cover from 1/25 to 1/4 inch long.

What it eats

A straw in the stem, for life.

Scale push tiny mouthparts into stems and leaves and drink the sap. Leaves yellow and drop, and twigs can die back.

Where it lives

Where the sap runs.

A houseplant with scale along its stems and leaf veins

Stems and leaf veinsThe adults.

Lined up along the plant's plumbing.

New growthThe crawlers.

Walking off to find a spot of their own.

Under the coverThe eggs.

Many kinds keep them under the shell.

How they grow up ↓

The life cycle

Crawl first. Then settle for good.

Crawlers hatch, wander, then settle. Once they settle, their legs drop off.

Egg

Under the mother's cover.

Crawler

Yellow to orange. The only stage that moves.

Settled

Growing its cover.

Adult

Under its finished cover.

Swipe for the next stage →

Spray droplets beading on scale covers along a stem

Why sprays miss

Armor is the point.

A hard cover keeps sprays out, and some systemic insecticides don't control armored scale at all.

Who's guarding them ↓

Strange company

The ants are farming it.

Soft scale drips honeydew. Ants guard it to keep the supply coming, and they attack beetles too.

Who eats scale? Two beetles.

What to get

Find the right beetle in two questions.

Question 1 of 2

Which did your scale do?

Question 2 of 2

How many plants?

Count every plant with scale, not just the worst.

How to count

Count a typical six-inch plant as 1, a large 8 to 10 inch plant as 2, a dense shrub or specimen as 3 to 4. A potted citrus by its leaves; between two sizes, the larger.

See all picks

Find the right beetle in two questions.
If you see	Our pick	Why
It pops off dryArmored scale	Rhyzobius lophanthae	Rhyzobius, for armored scale.
It squashes wetSoft scale. Sticky leaves usually mean this one	Cryptolaemus montrouzieri	Cryptolaemus, for soft scale.
I scraped a few and got bothSome pop off dry, some squash	Rhyzobius lophanthae	Rhyzobius, for a mix.

Our suggested plan

The crawlers set the pace.

1
Release day
The beetle for your scale.
Onto the worst stems.
2
Every 2–3 weeks
Another round.
While crawlers keep turning up.
✓
Stop
No new crawlers for two weeks.
You're done.

A light case may need just one round. Go by the crawlers, or ask us.

How to release

Ants first. Then beetles.

Before it arrives

Confirm it's scale. Small shells along the stems and veins.

Take yellow cards down. Adult beetles fly, and the cards catch them.

Wait out any spray.

Once dryNeem or horticultural oil

1 dayInsecticidal soap

21 daysSulfur

NeverSystemic insecticides

Another product? Tell us its active ingredient. The label's wait wins if it's longer.

Cartoon: a sticky band around a plant stem to stop ants — **Stop the ants.**
Bait or block them 2 to 3 days before.

Release day

Cartoon: misting a stem, then opening a tube right against it — **Mist, then open at the scale.**
The day they arrive, right against the stems.

Cartoon: releasing beetles onto the worst of three plants — **Start on the worst plant.**
Then the next worst.

What to expect

Look for crawlers, not shells.

A Rhyzobius beetle feeding on armored scale

Right after release
Small, dark, quick beetles are Rhyzobius. White, woolly larvae that pass for mealybugs are Cryptolaemus. Both are ours.
As it takes hold
Rhyzobius larvae are scruffy and gray, like tiny alligators. Leave them be.
When it's working
Fewer new crawlers, and dry, chewed shells.

Live crawlers still turning up? Go again.

Why treatment fails

Too soon, too far, too wet.

Cartoon: a calendar with four weeks marked beside a plant

1

Judged too soon.

Scale is slow. Give it about four weeks.

Cartoon: beetles let out on a clean plant while the scale is on another

2

Released far from the scale.

The beetles do their best work right on the colony.

One less common reason

A wet spray at release. It coats and kills the beetles.

Cartoon: a hand checking the stems of a new plant

Prevention

Scale picks favorites. So can you.

Most scale stick to a few kinds of plant. If one plant keeps getting it year after year, it may be worth growing something scale leaves alone.

Field Notes

Scale, under the shell.

Questions

Shells, beetles and the odd male.

Will the beetles fly away?

While there's scale to eat, they stay. Once it's gone, the adults fly off to find more.

Can I use a systemic insecticide too?

No. A systemic moves into the scale and reaches the beetle eating it.

Do scale insects have males?

Some do. They're tiny, delicate and winged, and rarely seen. Some kinds have no males at all.