What is eating holes in my leaves?

Q: What is eating holes in my leaves?

Holes in cannabis leaves are usually chewing pests, and the clue left behind names them. Dark frass pellets mean caterpillars; silvery slime trails mean slugs or snails; ragged margins on outdoor edge plants mean grasshoppers; a seedling cut through at the soil line means cutworms. Indoors, chewers are rare: holes there are more often dead, dried tissue from nutrient or burn spots falling out. Check at night with a torch.

Short answer

Holes in cannabis leaves mean a chewer, and the evidence it leaves tells you which: frass for caterpillars, slime for slugs, ragged edges for grasshoppers, cut stems for cutworms. Indoors, holes without frass are usually dead spots dropping out, not pests. Established.

Why

Caterpillars leave droppings. Young larvae chew small holes in leaves; older corn earworm larvae, up to about 25 mm (1 in), bore into buds, and their frass lets bud rot in ^[1]^[3].

Outdoor chewers come from the surroundings. Grasshoppers move in from field edges in dry summers, and cutworms hide in soil by day and cut young stems at night; both are listed among hemp pests ^[2].

Slugs and snails feed at night and in wet weather, leaving ragged holes and slime on seedlings and low leaves.

Leafminers make tunnels, not holes: pale winding trails inside the leaf ^[4].

Indoors, chewing pests are uncommon and usually arrive through open intakes or doors ^[1].

The numbers

Clue	Likely cause	Where
Holes plus dark frass pellets	Caterpillars	Outdoors mostly; buds in flower
Ragged holes plus slime trails	Slugs, snails	Seedlings, low leaves, after rain
Missing leaf margins, edge plants first	Grasshoppers	Outdoors, dry summers
Seedling cut at soil line	Cutworm	Fresh outdoor transplants
Pale winding trails	Leafminer	Fan leaves
Brown-edged holes, no frass	Dead spots falling out	Indoors

What to do

Look on and under leaves at dusk and after dark with a torch.
Search for frass, slime, larvae and cut stems.
Hand-pick caterpillars, slugs and cutworms; bag damaged bud sections.
Use stem collars on transplants and fine netting where practical.
From early flower, scout upper colas twice weekly for eggs and frass.
Indoors with no frass, check nutrients, pH and spray or light burn.

Common mistakes

Spraying before identifying the culprit.
Ignoring leaf holes in late summer until buds rot.
Using Bt on large larvae already inside buds.
Blaming insects for nutrient spots indoors.

Full article: Caterpillars and budworms on cannabis
Answer: What can I spray in flower?
Article: Rust or brown spots on leaves
Terms: slugs and snails · cutworm · grasshopper · leafminer

Follow-up questions

What is eating my cannabis leaves at night?

Leaves of cannabis eaten overnight point to night feeders: slugs and snails, which leave ragged holes and silvery slime trails, caterpillars, which leave dark frass pellets, and cutworms, which chew young stems through at the soil line. Go out an hour or two after dark with a torch, especially after rain, and look on and under the leaves and around the stem base.

Why are there holes in my leaves indoors with no bugs?

Holes in indoor cannabis leaves with no bugs and no frass are usually dead tissue falling out, not feeding. Brown or rust spots from nutrient problems, spray burn or light burn dry out and crack away, leaving holes with brown edges. Chewing pests are uncommon indoors and usually arrive through open intakes or doors. Check leaf undersides with a lens before blaming insects.

Do I need to treat for caterpillars if I see holes?

A few caterpillar holes in fan leaves cost little, but they warn you that moths are laying eggs, and in flower the larvae bore into buds and start bud rot. Hand-pick larvae at dusk or dawn, scout upper colas for eggs and frass from early flower, and use fine netting where practical. Bt works only on small larvae, under about 12 mm (0.5 in).