Cabbage moths and other caterpillars (Helicoverpa, loopers): how to identify them and when to spray

Cabbage moths and other caterpillars are a named pest group on the Py-Bo label (APVMA 53738). In Australian horticulture that group is the surface-feeding larvae that chew fruit, vegetables, cut flowers and ornamentals: diamondback moth (cabbage moth, Plutella xylostella), Helicoverpa / heliothis (Helicoverpa armigera and H. punctigera), loopers (Chrysodeixis spp.), cabbage white (Pieris rapae) and other leaf-eaters.

They devalue a crop fast. A couple of days of unnoticed hatch can window leaves, foul heads with frass, or put holes in fruit and florets. Once a larva is inside a stem, cob, nut or fruit, a foliar contact spray cannot reach it. This page is about hitting larvae while they are still on the plant.

This page is for commercial Australian growers and anyone searching cabbage moth, diamondback moth, Helicoverpa, heliothis, tomato grub, loopers, cabbage white or caterpillar spray. It covers identification, life cycle, spray timing, and how to use Py-Bo (80 g/L pyrethrins + 320 g/L piperonyl butoxide, EC) as a contact spray. Always read the current APVMA-approved label. The label is the law.

Cabbage moth and other caterpillars are named pests on the Py-Bo label (APVMA 53738) for fruit and vegetable crops, cut flowers and ornamental plants. That is an on-label pest group. It is not a licence to spray every moth species on every crop. Use only the crops, pests and situations named on the current label. This page does not authorise off-label use.

Identification and symptoms

Caterpillars chew. They have mandibles, not a sucking beak. In a heavy infestation you can hear them. Disturbed larvae often drop on a silk thread (they abseil). Loopers walk by looping: hind prolegs plant, front end reaches forward, body arches, rear comes up. That is how you separate them from Helicoverpa in the row.

Cabbage moth (diamondback moth, Plutella xylostella)

This is the moth Australian brassica growers mean by cabbage moth. Adult about 10 mm, grey-brown. At rest the folded wings show a row of pale diamond marks down the back. Eggs are pale yellow, flat, oval, about 0.5 mm, on leaves (often beside veins or on the underside). Young larvae mine inside the leaf for a day or more, then feed on the underside. Mature larvae about 10 mm, plump, bright green, tapered at both ends; they wriggle backwards and drop on silk when disturbed. Pupae sit in a gauze-like silk cocoon on the plant — including inside broccoli florets and cauliflower curds.

Damage: pinholes, then “windows” (epidermis left), then tattered leaves. They tunnel into cabbage heads and Brussels sprouts and feed in florets. Once they are inside the head they are almost impossible to hit with a spray. Frass and cocoons in the product make it unsaleable. Life cycle can be under 20 days in hot dry weather. Overlapping generations. Known resistance to synthetic pyrethroids and several other groups in Australia.

Helicoverpa / heliothis (Helicoverpa armigera and H. punctigera)

Still called heliothis in many sheds. Also tomato grub, corn earworm, native budworm, cotton bollworm. Eggs are pearly white, ribbed, about 0.5 mm, laid singly on leaves, buds, flowers and developing fruit (often the top third of the plant). Colour shifts white → brown → black-head before hatch. Larvae grow to 40 mm, colour green, pink, buff or brown, with side stripes and sparse stiff hairs. H. armigera large larvae have a dark saddle on the fourth segment and white hairs around the head; H. punctigera lack the saddle and have black hairs around the head. Pupae are reddish-brown in a soil cell 5–10 cm deep. Moths fly at night.

Damage: chew leaves, buds and flowers, then bore into fruit, pods, lettuce hearts and sweet-corn cobs (down the silk channel). Large entry holes; rot follows. Target small larvae on the surface. H. armigera is the harder of the two because of insecticide resistance. Hosts include tomatoes, capsicum, chilli, beans, peas, lettuce, brassicas, sweet corn, greenhouse veg, ornamentals and cut flowers — plus many field crops and weeds.

Loopers (Chrysodeixis spp.)

Vegetable looper (C. eriosoma), tobacco looper and related green loopers. Eggs pale yellow-green, slightly flattened, on the undersides of leaves. Larvae green with faint white lines, up to about 40–50 mm, only two pairs of abdominal prolegs — that is the looping walk. They chew large ragged holes, window young leaves, and can bore into heads, flowers and pods. Pupae in a thin silk cocoon on the underside or in a folded leaf. Hosts: leafy veg, brassicas, beans, tomatoes, potatoes, greenhouse crops, herbs and many ornamentals.

Other leaf-eaters on the same labelled group

Cabbage white (Pieris rapae): day-flying white butterfly, not the small grey cabbage moth. Velvety green larva with a thin yellow stripe; chews large irregular holes from the leaf edge; dark-green frass on the product.
Cabbage cluster caterpillar (Crocidolomia pavonana): larvae feed in groups; webbing and frass over cabbage heads.
Cluster caterpillar (Spodoptera litura): young larvae skeletonise together; older larvae chew holes separately.

Do not confuse these with borers that spend almost their whole larval life inside fruit, nuts or shoots (codling moth, oriental fruit moth, yellow peach moth, macadamia nut borer). Those may be “caterpillars”, but once they are inside they are not a foliar contact job. See what Py-Bo will not do.

Life cycle (what you are spraying, and what you are not)

Moths and butterflies lay eggs. Larvae chew. Pupae do not feed. Adults fly and lay the next lot. Warm weather shortens every stage. Helicoverpa runs egg to adult in about 5–7 weeks in summer. Diamondback moth can do it in less than 20 days. Generations overlap, so eggs, larvae and pupae are on the block at the same time.

Stage	Where	Rough timing	Hit by a foliar contact spray?
Egg	On the leaf, bud, flower or fruit surface (often undersides). Tiny.	Hatch ~3–8 days in warm weather	No — not reliably. Too small, often missed, not a feeding target.
Young larva (DBM first instar)	Mining inside the leaf for a day or more	~1–2 days	No — inside the leaf
Feeding larva on the plant	Undersides, hearts, new growth, flowers, fruit surface	~1–3 weeks (species and temperature)	Yes — if droplets contact them, including undersides. Disturbed larvae may drop on silk before the boom arrives.
Larva inside fruit, cob, nut, floret, head or stem	Inside plant tissue	Until they finish feeding	No
Pupa on the plant (DBM, loopers, cabbage white)	Silk cocoon or chrysalis on leaf, stem or in florets	~5–14 days in season	Only if a droplet hits the pupa — not a reliable kill, and a cocoon inside a floret is not contacted
Pupa in soil (Helicoverpa)	Soil cell 5–10 cm deep	~2 weeks in summer; overwinters in diapause	No
Adult moth / butterfly	Canopy; most moths fly at night	About 10 days (Helicoverpa); shorter for some moths	Only if droplets hit the insect

Beneficials (Diadegma on diamondback moth, Trichogramma on Helicoverpa eggs, predatory bugs, spiders) help. They are support, not a commercial guarantee when the buyer is counting holes. A contact spray will also kill beneficials it hits.

When to spray

Spray when larvae are on the plant and you can see feeding, frass or caterpillars. Contact insecticides only kill what they hit. Eggs, leaf-mining first instars, pupae in soil, and larvae already inside fruit or heads keep the cycle going.

Scout twice a week in warm weather. Hatch can run away in a couple of days. Shake plants over a sheet for Helicoverpa. Check undersides for diamondback moth and loopers. Look in hearts, florets and around fruit.
Target small larvae on the surface. Helicoverpa and diamondback moth are a different problem once they are in the cob, head or fruit.
Coverage is the job: undersides, inner wrapper leaves, growing tips, flower heads and the far side of the row. Missed tissue equals live caterpillars.
Expect larvae to drop on silk when the sprayer disturbs them. Slow enough, wet enough, and from more than one angle.
A spray that kills feeding larvae does not kill eggs already on the leaf. Those eggs can still hatch in about 3–8 days. Diamondback moth first instars then spend a day or more inside the leaf.
Plan a follow-up about 7–14 days after the first spray, when the next hatch is visible — sooner at peak diamondback moth pressure in heat. Do not treat Py-Bo as a six-week “protection” interval.
Helicoverpa pupae already in the soil can emerge and start laying after you spray. Adults also fly in from weeds and neighbouring crops.

Bees: pyrethrins are dangerous to bees. The Py-Bo label says do not spray any plants in flower while bees are foraging. Apply after dark, when bees are in the hive. Residues continue to keep bees off treated surfaces into the next morning until UV degrades the pyrethrins (often around mid-morning). Do not treat as bee-safe in daylight on open flowers.

How to spray Py-Bo

Product: Py-Bo Natural Pyrethrum Insecticidal Concentrate (APVMA 53738)
Actives: 80 g/L pyrethrins + 320 g/L piperonyl butoxide (PBO), emulsifiable concentrate
Mode: contact only. Knockdown of insects the spray actually hits. Not systemic. Not residual in the plant. Pyrethrins break down rapidly in sunlight.
Labelled horticultural situation: fruit and vegetable crops, cut flowers and ornamental plants.
Labelled horticultural pests: aphids, ants, cabbage moth and other caterpillars, earwigs, leafhoppers, thrips, whiteflies.
Rate on that labelled horticultural use: 1 mL Py-Bo per 1 L water, or 100 mL per 100 L water. Do not invent another rate.
Withholding period: 1 day on labelled edible plants (do not harvest for 1 day after application). Confirm crop listing and WHP on the current label.

Cabbage moth and other caterpillars are the named pest group. Helicoverpa / heliothis, loopers and leaf-eating caterpillars sit in that group when they are on labelled fruit, vegetables, cut flowers or ornamentals and the spray can contact them. That is not a claim for every moth on every crop, and it is not a claim against borers already inside tissue. Check the current APVMA-approved label (and any current APVMA permit) for your crop and pest before you spray. This page does not authorise off-label use.

Mix 1 mL/L (100 mL/100 L) in clean water only if that is the rate on the label for your situation.
Apply so droplets contact larvae on foliage, flowers and fruit, including undersides and inner leaves. Thorough coverage of all foliage, including undersurfaces, is what the label requires on the horticultural use.
Prefer dusk / after dark. Do not spray plants in flower while bees are foraging.
If live larvae remain after the spray has dried, they were not contacted — or they dropped on silk. Change volume, droplet size or nozzle angle on a test run.
Follow up about 7–14 days later if the next hatch is visible.

Py-Bo is APVMA-approved for listed uses. Use only on crops, pests and situations named on the label. This page does not authorise off-label use.

What Py-Bo will not do

Will not kill borers already inside stems, fruit, nuts, cobs or florets. Codling moth in apples, oriental fruit moth in stone fruit, yellow peach moth in tropical fruit, macadamia nut borer in the kernel, Helicoverpa down a cob or inside a tomato, diamondback moth inside a cabbage head — contact pyrethrum does not move in sap and does not reach larvae inside tissue.
Will not reliably kill eggs on the leaf.
Will not kill diamondback moth larvae while they are mining inside the leaf.
Will not kill Helicoverpa pupae 5–10 cm in the soil, or other pupae the spray never hits.
Will not give a season-long residual. UV degrades pyrethrins; that is why WHP is one day and why you re-treat on hatch, not on a six-week “protection” interval.
Will not spare parasitoids and predators it hits.
Will not replace coverage. Contact product, contact required.
Will not make an unlabelled crop or pest legal. Named crops and named pests only. The label is the law.

FAQ

Are cabbage moths the same as cabbage white butterflies?

No. In Australian brassicas, cabbage moth usually means diamondback moth (Plutella xylostella) — a small grey moth with diamond marks on the back. Cabbage white (Pieris rapae) is a day-flying white butterfly with a velvety green caterpillar. Both chew brassicas. Both sit in the labelled “cabbage moth and other caterpillars” group when they are on labelled vegetable or ornamental uses. Identification still matters for monitoring and resistance management. Diamondback moth is the harder pest.

Is Helicoverpa / heliothis on the Py-Bo label?

The current public Py-Bo label (APVMA 53738) names cabbage moth and other caterpillars as a horticultural pest group, on fruit and vegetable crops, cut flowers and ornamental plants. It does not list Helicoverpa species by scientific name. Helicoverpa / heliothis, loopers and leaf-eaters are the commercial “other caterpillars” when larvae are exposed on those labelled uses. Confirm your crop and pest on the current label. This page does not authorise off-label use.

Will Py-Bo kill caterpillars inside fruit or stems?

No. Py-Bo is contact only. It is not systemic. Larvae already inside apples, stone fruit, tomatoes, sweet-corn cobs, nuts, florets or stems are not contacted. Spray while larvae are still on the leaf, flower or fruit surface. Once they have bored in, choose a product and strategy registered for that borer — that is a separate label decision.

What rate of Py-Bo, and what is the withholding period?

On the labelled horticultural use: 1 mL per 1 L of water (100 mL per 100 L). The withholding period on labelled edible plants is 1 day. Always confirm the crop, pest and WHP on the current APVMA-approved label. Do not invent rates.

Will one spray fix it for the season?

No. Py-Bo is a contact knockdown with no residual. Missed eggs hatch in a few days. Diamondback moth first instars mine the leaf. Helicoverpa pupae in the soil still emerge. Adults fly in. Plan a follow-up about 7–14 days later when the next hatch is visible, and keep scouting. Diamondback moth can turn over in less than three weeks in heat.

What about bees?

Dangerous to bees. Do not spray any plants in flower while bees are foraging. Spray after dark when bees are in the hive. Residues keep bees off treated surfaces into the next morning until UV degrades the pyrethrins. Do not treat it as bee-safe in daylight on open flowers.

What about codling moth, oriental fruit moth and nut borers?

Those larvae feed inside fruit, shoots or nuts. A foliar contact spray can only hit a larva in the short window after hatch, before it enters. It will not kill a larva already inside. Do not treat this page as a codling moth, oriental fruit moth or macadamia nut borer registration. Named crops and named pests only.

Quick reference

Label pest group: cabbage moth and other caterpillars (APVMA 53738) — this is an on-label group
Common names: cabbage moth, diamondback moth, Helicoverpa, heliothis, tomato grub, corn earworm, native budworm, loopers, cabbage white, leaf-eating caterpillars
Scientific names: Plutella xylostella; Helicoverpa armigera, H. punctigera; Chrysodeixis spp.; Pieris rapae and other leaf-eaters
Labelled crops: fruit and vegetable crops, cut flowers and ornamental plants (named uses only)
Symptoms: windowed or holed leaves, frass, chewed flowers, holes in fruit/heads; larvae may drop on silk when disturbed
Eggs: on the plant surface; hatch ~3–8 days in warm weather; not a reliable contact kill
Larvae (contact window): on undersides, hearts, flowers and fruit surface. Not once inside tissue. DBM first instar mines the leaf.
Pupae: DBM/loopers in silk on the plant; Helicoverpa 5–10 cm in soil (not contacted)
Spray timing: on live surface larvae and fresh chewing; follow-up ~7–14 days if the next hatch is visible; after dark if bees are working
Py-Bo: 80 g/L pyrethrins + 320 g/L PBO; labelled horticultural rate 1 mL/L (100 mL/100 L); 1 day WHP on labelled edible plants; contact only. Will not kill borers inside stems or fruit.

Always read and follow the current APVMA-approved label. The label is the law. Named crops and named pests only. Py-Bo is available through Pestech Australia’s Ag resellers or direct.