Two pests explain almost every holey kale leaf: white butterfly caterpillars, or slugs and snails. Check for a slime trail before doing anything else — trail present means slugs or snails, no trail with droppings or hovering white butterflies nearby means caterpillars. A scatter of many tiny round holes on a young seedling instead of a few big ones points to flea beetle, a less common third option worth ruling in only if the plant is still small.

Ranked, most likely first

  1. White butterfly caterpillars. The cabbage white butterfly lays eggs on leaf undersides; the caterpillars that hatch chew irregular holes that start small and spread fast. Droppings on the leaf or adult butterflies fluttering around the bed confirm it.
  2. Slugs and snails. Ragged holes and chewed leaf edges look similar at first glance, but the silvery slime trail left behind is the tell caterpillars never leave. They feed at night and shelter somewhere damp and dark through the day.
  3. Flea beetles. Dozens of tiny round punctures rather than a few large holes, almost always on young seedlings or fresh transplants rather than established plants. Worth checking for, but less commonly the culprit here than the two above.

Why this zone leans toward slugs and snails

Kale's sowing and transplant dates don't change by zone — August to October to sow, September to November to transplant, Egmont-sourced — so a young, tender plant is going into cool/mountain ground at the same point on the calendar as anywhere else in the country. What differs is how the two main pests respond to a colder, slower-warming spring here. White butterfly activity is temperature-driven, so it tends to build later and stay lighter through a cool/mountain spring than further north. Slugs and snails run the other way: they're most active in cool, damp conditions, and this zone holds onto both for longer into the season. If holes show up on a cool/mountain kale bed, slugs and snails are a genuinely stronger first guess here than they'd be in a warmer garden — check for the slime trail before reaching for anything caterpillar-specific.

Fixing it

  • Confirm the cause before treating it. A slime trail means slugs or snails; irregular holes with droppings or butterflies nearby mean caterpillars. Treating for the wrong one wastes a week.
  • Caterpillars: hand-pick eggs and small caterpillars off leaf undersides, and net the bed with insect mesh weighted down at every edge — this is the single most effective step against white butterfly and is worth having in place from transplanting, not after damage shows. For the full identification and spray options (including how this pest differs from diamondback moth, which also turns up on brassicas), see White Butterfly and Cabbage Moth on NZ Brassicas.
  • Slugs and snails: clear the damp hiding spots near the bed first — pots, boards, dense mulch pulled right up against the stems — then add a barrier or bait if pressure keeps up. A cool/mountain garden holds the damp conditions these pests want for longer, so this is worth doing as routine maintenance here, not just once when damage appears. Full control options are in Slugs and Snails in the NZ Vegetable Garden.
  • Flea beetles: a floating row cover from transplanting protects tender young growth, which is the stage they target; damage tapers off once the plant is established.

Cultivar notes

Kings Seeds NZ lists autumn, early spring, and late summer sowing across its kale range — Blue Ridge F1, Cavolo Nero, Noble, and Red Russian all carry the same sowing window options. Sowing later in that range, once the spring caterpillar build-up has eased, is a genuine way to sidestep the worst of the pressure rather than relying on netting alone. None of the sourced cultivar notes claim pest resistance specifically, so pick on those sowing-timing grounds rather than expecting one variety to shrug off holes better than another.

Next season

Have insect mesh ready before transplanting rather than after the first holes appear — it's the one step that heads off both caterpillars and flea beetles at once. Clear damp shelter near the bed as routine maintenance through the cooler, wetter stretches of the season rather than only after slug damage turns up, since that's when this zone's conditions favour them most.

More on this zone: see the full NZ Cool/Mountain Planting Calendar →.