Tiny black specks on leaf surfaces

Likely causes, most likely first

Ranked for this sign on its own. Your stage, medium and readings change the order, so run the checker for your plant.

1. LikelyThrips

   PestDeal with it this weekRead: Thrips on cannabis: life table, temperature, scouting and biological control

   Fix: Two levels: predatory mites (Neoseiulus cucumeris, Amblyseius swirskii) or Orius on the foliage, plus soil predators (Stratiolaelaps scimitus) or Steinernema nematodes in the medium where they pupate. Blue or yellow cards to monitor. Sprays only in veg.

   Recovery: Card counts fall and no new silvering on new leaves within 2-3 weeks.

   How to confirm it

   • Magnifier check of leaf undersides and new growth. Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth.
   • Tap a branch over white paper. Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier.
   • Sticky cards for 1-2 weeks. Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby.

Look for

10x photo of black faecal dots on pale, scraped patches..