Pests

Scale insects

Also called: soft scale, brown scale, armoured scale

Small brown or tan bumps glued to stems and leaf veins that do not move — until you look closely.

What you'd see

Raised oval bumps, 2–5 mm, brown, tan or white, along stems and leaf midribs
Bumps flick off with a fingernail and leave a pale mark
Sticky honeydew and sooty mould (soft scales only)
Yellow patches on leaves above a colony; general lack of vigour

Where to look

Undersides along the main vein, stems, and where petioles join the stem. Ficus, citrus, ferns and bay are favourites.

How it spreads

The adults are fixed in place; the near-invisible crawlers walk to new leaves and neighbouring plants.

Is it really this? Look-alikes

Fern spores — Spore cases on ferns are arranged in neat regular rows or patterns on the underside; scale is scattered.
Natural stem bumps (lenticels) — Lenticels do not flick off and are evenly distributed.

What's going on

Scale insects settle as crawlers, push in a feeding tube and never move again, building a shell over themselves. Soft scales stay attached to their shell and excrete honeydew; armoured scales build a separate hard cover and do not.

Their shell is the reason sprays bounce off. The crawler stage, lasting a few days, is the only time contact treatments reach them.

Why?

Once you know only crawlers are vulnerable, the strategy is obvious: scrape off adults by hand now, and spray repeatedly over several weeks to catch each generation of crawlers as it hatches.

Grandmother's remedies

What people have always done — with an honest note on each.

Fingernail and alcohol
Scrape each bump off with a nail or old toothbrush; dab the spot with rubbing alcohol on a cotton bud.
Verdict: Still the most reliable method for houseplants. Slow, thorough, works.
Soap and old toothbrush
Scrub stems gently with mild soapy water.
Verdict: Good for removing adults on woody-stemmed plants like ficus.

Modern remedies

What growers and extension services reach for today.

Horticultural oil
Sprayed to smother crawlers and young scale every 7–10 days for 4–6 weeks.
Verdict: The best spray option; oil smothers where soap cannot penetrate.
Systemic insecticides
Soil-applied products carried in the sap.
Verdict: Effective on soft scales; less so on armoured scales, which feed differently.

Honest verdict

Scale is a marathon. A plant that looks clean after scraping is not finished — crawlers hatch for weeks. Set a reminder and check every Sunday for six weeks.

Prevention

Inspect stems and midribs of new plants under bright light
Keep plants vigorous — scale settles hardest on weakened plants
Wipe leaves seasonally

Plants this commonly troubles

Monstera Fiddle-leaf fig