White spots on cannabis leaves can come from a few different issues.

Common Causes for White Spots

Biological causes

Powdery mildew:

Looks like a fine white powder on leaves.

Usually starts as small spots, spreads fast in high humidity or poor airflow.

Spider mites:

Tiny pests that suck sap, leaving small white/yellow speckled dots.

Flip leaves over to check for moving dots or fine webbing.

Other pests (thrips, leaf miners, etc.):

Thrips can cause silvery-white streaks or spots.

Leaf miners make winding white trails inside leaves.

Environmental and nutrient causes

Light burn / bleaching:

If spots are near the top under strong LEDs or HPS, too much light intensity may bleach tissue.

Nutrient deficiencies:

Calcium deficiency sometimes shows as irregular white or light spots.

Usually comes with other leaf damage (brown edges, curling).

What to Do about the White Spots

1.Inspect the undersides of leaves with a magnifying glass for mites or thrips.

2.If you see powdery mildew, lower humidity (below 50%), increase airflow, and treat with organic fungicides (sulfur, potassium bicarbonate, or neem-based sprays in veg stage).

3.If it’s light burn, raise your lights or reduce intensity.

4.Check your nutrient mix and pH to rule out deficiencies.