Most holey kale comes down to one of two culprits: white butterfly caterpillars, or slugs and snails. The quickest way to tell them apart is a slime trail — present, and it's slugs or snails; absent, with droppings on the leaf or butterflies fluttering nearby, and it's caterpillars. A cluster of many small round holes on a young seedling rather than a few large ones suggests flea beetle instead, a less common third cause.

Ranked, most likely first

  1. White butterfly caterpillars. Eggs go on the underside of the leaf; the caterpillars that emerge chew irregular holes that start small and get bigger quickly. Spotting droppings, or the adult butterfly itself hovering around the bed during the day, both confirm it.
  2. Slugs and snails. The damage pattern — ragged holes, edges chewed away — can look similar, but they always leave a silvery slime trail behind, which caterpillars never do. Look for them, or their trail, in the evening or early morning; they hide somewhere damp during daylight.
  3. Flea beetles. Instead of a few large holes, dozens of tiny round punctures across the leaf — a "shot hole" pattern almost always seen on young seedlings or freshly transplanted kale rather than mature plants. Worth checking for on a young plant, but less often the actual cause than the two above.

Why caterpillars are the sharper first guess here

Kale goes in on the same calendar everywhere in the country — sow August to October, transplant September to November, harvest November to January, per the Egmont guide — so timing itself isn't what sets this zone apart. What differs is how fast the two main pests get going each spring. Temperate soil and air warm up faster than in a colder zone, and white butterfly activity tracks temperature closely, so caterpillar pressure tends to build earlier and stay steadier right through the transplant window here. Slug and snail activity, by contrast, is driven by cool, damp conditions, and those ease off sooner here as the season dries out. Put together: if holes show up on temperate kale, caterpillars are the stronger opening bet, though it's still worth a quick check for the slime trail before treating for one over the other — the balance runs the other way in a colder garden (see Why Is My Kale Full of Holes in NZ Cool/Mountain?).

Fixing it

  • Rule the cause in or out first. No slime trail plus droppings or butterflies nearby points to caterpillars; a visible trail points to slugs or snails instead. Getting this step right saves treating for the wrong pest.
  • For caterpillars, check leaf undersides every few days for eggs and small larvae and pick them off — cheap and effective while numbers are low. A well-sealed insect mesh over the bed from the moment plants go in is the strongest single step, since it stops the butterfly laying eggs in the first place. If pressure gets ahead of that, Yates Success Ultra (spinetoram) or the organic-approved Yates Nature's Way (pyrethrum and canola oil) are both labelled for use on edible crops. More detail on telling this pest apart from diamondback moth, which also turns up on brassicas: White Butterfly and Cabbage Moth on NZ Brassicas.
  • For slugs and snails, take away their daytime cover — pots, boards, mulch pushed up against the stems — before reaching for bait. A band of crushed eggshell or similar sharp material around the bed, or a trap checked regularly, both cut numbers without chemicals; pelleted bait works too but shouldn't touch the edible parts of the plant. Full walkthrough: Slugs and Snails in the NZ Vegetable Garden.
  • For flea beetles, cover seedlings and new transplants with row cover or insect mesh — that's when the damage is worst, and it drops off once the plant hardens up.

Cultivar notes

Kings Seeds NZ's kale range — Blue Ridge F1, Cavolo Nero, Noble, and Red Russian — all give the same three sowing windows: autumn, early spring, or late summer. None of the sourced notes claim any of these hold up better against pests, so the useful lever isn't which variety to plant but when: a later sowing, once the spring caterpillar surge has passed, sidesteps a good part of the pressure without extra netting or spraying.

Next season

Get insect mesh over the bed before transplanting rather than reaching for it once holes appear — caterpillar pressure builds fast here once spring warms up, and covering early beats treating late. Keep the same eye out for slime trails through any damp spell, since slugs and snails don't disappear here, they just lose ground to caterpillars as the faster driver of damage.

More on this zone: see the full NZ Temperate Planting Calendar →.