Two pests cause almost every case of holey kale, and one physical clue splits them apart instantly: look for a silvery slime trail. Find one and you're dealing with slugs or snails; find none, but droppings or hovering white butterflies nearby, and caterpillars are the culprit instead. A different pattern altogether — many small round punctures scattered across a young seedling rather than a handful of large ragged holes — points to flea beetle, a rarer third cause worth knowing about.

Ranked, Most Likely First

  1. White butterfly caterpillars. Eggs are laid on the leaf underside, and the caterpillars that hatch chew irregular holes that start small and grow fast. Droppings on the leaf, or adult white butterflies hovering around the bed, both confirm it.
  2. Slugs and snails. The ragged holes and chewed edges can look similar to caterpillar damage, but a silvery slime trail is the tell caterpillars never leave. They feed at night and shelter somewhere damp and shaded through the day.
  3. Flea beetles. Dozens of tiny round "shot holes" rather than a few large ones, almost always on young seedlings or fresh transplants rather than established plants — a less common cause, but distinctive enough to rule in at a glance.

Why This Zone Doesn't Get a Break From Either Pest

Kale follows the same calendar everywhere in NZ — sow August through October, transplant September through November, harvest November through January — so timing isn't what sets this zone apart. What does is that neither pest here gets the seasonal check the other zones see. Temperate gardens trade slug pressure for caterpillar pressure as the season dries out; cool/mountain gardens keep the reverse trade, damp conditions favouring slugs while cooler temperatures hold caterpillars back. This zone doesn't get that trade-off at all: warmth arrives earliest and lasts longest here, so caterpillar and flea beetle activity starts soonest and runs furthest into the year, while the humidity that comes with that warmth keeps things damp enough that slug and snail pressure never really eases the way it does once a drier zone's season turns. Netting against caterpillars and checking for slime trails both matter for a genuinely longer stretch of the calendar here than anywhere else this site covers.

Fixing It

  • Rule the cause in or out before treating anything. A slime trail means slugs or snails. Irregular holes with no trail, plus droppings or butterflies nearby, means caterpillars.
  • Caterpillars respond best to a habit of checking leaf undersides for eggs and small larvae and picking them off before numbers build. Sealing insect mesh over the bed from the day plants go in stops the butterfly laying eggs at all, which beats reacting to damage after the fact. If pressure gets ahead of that, two products are labelled for caterpillars on edible crops: Yates Success Ultra (spinetoram) and the BioGro-approved Yates Nature's Way (pyrethrum and canola oil). Telling this pest apart from diamondback moth is covered in White Butterfly and Cabbage Moth on NZ Brassicas.
  • Slugs and snails lose ground fastest once their daytime hiding spots go — pots, boards, and debris sitting near the stems. A crushed-eggshell band ringing the bed, or a trap emptied on a regular schedule, both bring numbers down without chemical input; pelleted bait is an option too, kept clear of anything actually edible on the plant. Slugs and Snails in the NZ Vegetable Garden covers the full approach.
  • Flea beetles are worth covering for specifically while seedlings and fresh transplants are still tender — row cover or insect mesh over that vulnerable stage handles most of it, since the damage tapers off once the plant toughens up.

Cultivar Notes

Kings Seeds NZ's kale range sourced for this zone — Blue Ridge F1, Cavolo Nero, Noble and Red Russian — all share the same three sowing windows: autumn, early spring, or late summer. Koanga Institute's Borecole takes a slightly different route: tray-sown, pricked out at 2.5cm spacing, transplanted at 40cm once around 8cm tall, or broadcast directly if you'd rather harvest it young for mesclun. None of the sourced notes claim better pest resistance for any of these, so variety isn't the lever here. Given how little seasonal relief this zone gets from either pest, netting from the day plants go in is worth treating as standard practice rather than an optional extra.

Next Season

Have insect mesh in place before transplanting rather than reaching for it once holes show up, and keep checking for slime trails through damp stretches for longer into the year than you might in a drier garden — neither pest genuinely stands down here the way it does further south.

More on this zone: see the full NZ Sub-Tropical Planting Calendar →.