SPRING & AUTUMN · DAMP NIGHTS
Slugs
Ragged holes and slime trails, worst in damp weather. Clemson calls slugs the most common hosta problem.
Crop hub · Garden · Home garden
Hostas
Ragged holes in the leaves, silvery slime trails and nothing visible by day mean slugs or snails. Clemson calls garden slugs the most common problem of hostas, and the RHS and UC IPM both single hostas out among the plants slugs damage. They feed at night and in damp weather, so go out with a torch on a mild, damp evening to confirm it before you do anything else.
The other culprits leave different evidence. Earwigs also chew ragged holes at night; the University of Minnesota lists hostas among their food plants, and a torch will show them too. Clemson notes that deer eat the leaves and part of the leaf stalks, and that voles eat the roots and kill the plant. Brown or yellow blotches that stop at the veins, showing up in late summer, are foliar nematodes. UW–Madison says they spread in water splash and that home gardeners have no chemical control, so the infected plant has to go.
No single slug control is reliable on its own, so combine them: remove daytime shelter, hand-pick, trap, and use iron phosphate if you bait at all. UC IPM warns that metaldehyde baits are particularly poisonous to dogs and cats.
crop context · hosta leaf with ragged slug holes
What eats hostas
SPRING & AUTUMN · DAMP NIGHTS
Snails
The same ragged holes as slugs, by night. Handled the same way: hand-pick, trap, remove shelter.
LATE JUNE–OCTOBER
Earwigs
Ragged holes at night. They also eat aphids, so trap them near the damage rather than spraying.
ReleaseNothing to releaseTrap in rolled newspaper; empty each morning
Season calendar
US GARDENS · QUALITATIVE READING OF EXTENSION SOURCES| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Slugs | Jan: Quiet | Feb: Quiet | Mar: Building | Apr: Pest pressure high | May: Pest pressure high | Jun: Pest pressure high | Jul: Building | Aug: Building | Sep: Pest pressure high | Oct: Pest pressure high | Nov: Building | Dec: Quiet |
| Snails | Jan: Building | Feb: Building | Mar: Building | Apr: Pest pressure high | May: Pest pressure high | Jun: Building | Jul: Building | Aug: Building | Sep: Building | Oct: Pest pressure high | Nov: Building | Dec: Building |
| Earwigs | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Quiet | May: Building | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Building | Nov: Quiet | Dec: Quiet |
- Pest pressure high
- Building
- Release window
- Quiet
- Slugs · high pressure Apr–Jun, Sep–Oct
- Snails · high pressure Apr–May, Oct
- Earwigs · high pressure Jun–Sep
Starter program
There is nothing to buy and release for hostas outside California. This is the order of jobs, starting as the shoots come up.
- AS SHOOTS EMERGEClear daytime shelterBoards, stones, debris and dense ground cover near the crowns; water in the morning
- MILD, DAMP EVENINGSHand-pick by torchlightRepeat through the season; slugs return to the same plants
- EACH MORNINGEmpty the trapsBoards raised about 1 inch off the soil, or beer traps sunk level with deep sides
- IF YOU BAITIron phosphateIn the late afternoon or evening; rebait the same spots. Never metaldehyde where pets roam
- ALL SEASONGround beetlesKeep permanent edges and cover for them, but do not expect predators alone to protect hostas
Setting up the garden
A good deal of what goes wrong with hostas is not an insect, and several fixes happen at planting.
Water at the base, in the morning
Ground that is dry by nightfall helps against slugs (UC IPM), and keeping water off the leaves limits foliar nematode spread (UW–Madison).
Inspect new plants
Clemson suggests buying hostas in late summer or autumn, when foliar nematode damage shows, and passing over plants that are yellow or brown between the veins.
Treat barriers with caution
In an RHS trial, copper tape, grit, eggshells, bark and wool pellets did not reduce slug damage. UC IPM does recommend copper sheet barriers at least 2 in (5 cm) tall.
Brown edges in sun are scorch
Too much sun fades colour and can cause leaf dieback, especially in dry spells. Blue hostas need shade, and variegated leaves scorch first on their pale sections (Clemson). No pest is involved.