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Break the pest life cycle: timing Py-Bo follow-up sprays

Break the pest life cycle: timing Py-Bo follow-up sprays

All plants are threatened by an insect pest at some stage of the year. Insects that evolved to eat plants will find one they like to eat. Those insects have a life cycle, and that life cycle is what you should aim to break.

One contact spray rarely finishes the job. Eggs hatch after you’ve sprayed, pupae come up out of the soil, and new adults fly in. This page explains the two kinds of insect life cycle and when to make the second spray. It then goes pest by pest through the insects named on the Py-Bo label for fruit and vegetable crops, cut flowers and ornamental plants.

Buy Py-Bo: 250 mL, 1 L, 5 L or 20 L · or ask at Nutrien Ag, E.E. Muir, Elders, Lindsay Rural or Fernland.

Product: Py-Bo Natural Pyrethrum + Piperonyl Butoxide Insecticidal Concentrate (APVMA 53738; 80 g/L pyrethrins + 320 g/L piperonyl butoxide). Always read the current label. The label is the law.

Breaking the life cycle

There are two main types of life cycle.

Egg – nymph – adult

Aphids, thrips, whiteflies, leafhoppers and others lay eggs (aphids can also give birth to live young). The eggs hatch into nymphs, and the nymphs shed their skin to become bigger nymphs. The last moult reveals an adult, ready to mate and lay more eggs.

Generally, the nymphs don’t leave the plant where their egg was laid. A contact spray will kill all the insects it hits, but that is not always the end of the infestation. Eggs are sometimes well protected and will hatch soon after the first spray. Make another spray before the oldest of those new nymphs become adults. By then the eggs have hatched, and there are no new adults to lay more eggs. The second application has broken the life cycle.

But thrips are the exception that proves the rule. Thrips hatch into nymphs, and when the third nymphal stage (the correct word is “instar”) is fully fed, it drops off the plant to the soil. The next stage doesn’t eat. Down in the soil it is busy turning itself into an adult with wings and reproductive organs, which takes a few days. Your first contact spray kills the adults and the nymphs on the plant. Thrips eggs are laid in slits in the plant tissue, so the contact spray has little effect on the eggs or on the stage in the soil. You need to spray again a few days after the first application. That kills the newly hatched nymphs and the newly emerged adults before they can mate and begin the next generation.

Life isn’t meant to be easy. Thrips can be carried long distances on the breeze, so a new invasion is always possible.

Systemic insecticides that run through the sap stream can be a better control method for some situations. Read their labels for the withholding period for your crop and whether your pest gets a mention. The label is the law. Contact killers such as natural pyrethrum, with a 1-day withholding period, have their place during the last weeks before harvest, or when you only need to treat part of a crop.

Egg – larva – pupa – adult

Moths and butterflies have a different life cycle. Eggs hatch into larvae (caterpillars). When the larvae are fully fed, they pupate, often in the soil, and change into adults. Eggs are laid where the hatching larvae can start feeding straight away, usually on the host plant, so the young caterpillars get straight into the leaves (or burrow into fruit, heads or nuts). Most adult moths and butterflies don’t feed on the crop.

Breaking this type of life cycle is much more difficult. You can spray the caterpillars on your plants and kill every one you hit, but moths and butterflies fly in over your boundary from distant parts and lay more eggs. A contact insecticide such as Py-Bo is great at rescuing a threatening situation. That takes you back to the first rule: look at your crop, often.

When to make the second spray

The Py-Bo label directs you to spray to contact the pests when infestation occurs. It does not set a repeat interval. The timings below are grower guidance from Pestech’s articles and Pest List, not label directions. Base the follow-up on what you see: fresh nymphs, new larvae, or adults flying back in.

  • Thrips: about 3–5 days after the first spray, to catch adults coming up out of the soil before they lay.
  • Aphids: check again within a week and re-spray if live aphids are building.
  • Leafhoppers: about a week later, to catch nymphs hatching from eggs in the leaf before they become adults.
  • Whiteflies: when young nymphs and adults are visible again on the undersides.
  • Caterpillars: about 7–14 days later if the next hatch is visible. Go sooner at high diamondback moth pressure in hot weather.
  • Earwigs and ants: when they are back on the plant. Spray earwigs at dusk.

Pest by pest: life cycles and spray timing

Aphids

  • Common pests: green peach aphid, tomato aphid, rose aphid, black citrus aphid, cabbage aphid and many other species.
  • Identification: adults about 2–3 mm, mostly wingless in the warm months, with winged forms appearing in late autumn. Nymphs are smaller and wingless.
  • Life cycle: egg to adult in about 1–2 weeks, through 4 nymph stages. Females live about 4 weeks and give birth to 3–4 young a day. Males appear in autumn. Autumn eggs and mature females may overwinter.
  • Where they hide: growing tips, usually exposed. Some are found under leaves and inside curled flush.
  • Crops: vegetables, tree crops and flowers, indoors or outdoors.
  • Damage: growing tips distorted by sap loss. Honeydew turns black with sooty mould and marks the produce, and ants come to feed on it. Aphids may spread plant viruses.
  • What a contact spray hits: nymphs and adults on exposed tips and leaves are easy to contact, and Py-Bo kills them in minutes. Aphids inside tight curls are much harder to reach.
  • Follow-up: begin spraying in early spring as colonies start. Check again within a week and re-spray if live aphids are building. More on the aphid page.

Thrips

  • Common pests: western flower thrips, onion thrips, plague thrips and many other species.
  • Identification: small, slender insects, black to light brown or yellowish. Adults have two pairs of narrow, hair-fringed wings.
  • Life cycle: 4 nymphal stages in about 2 weeks. The third-stage nymph drops off the plant into the soil or growing medium and spends about 3–5 days changing before it flies back onto the crop. Females live about 4 weeks and lay 2–10 eggs a day, in slits in the plant tissue.
  • Where they hide: undersides of leaves; some prefer flowers. They often fly long distances, breeze-assisted, to a new crop.
  • Crops: nearly all crops, indoors or outdoors.
  • Damage: marked flowers, young fruit and leaf tissue, and flower and young fruit loss. They may spread plant viruses.
  • What a contact spray hits: most thrips on the plant are exposed and easily hit, and Py-Bo kills them in minutes. Eggs in tissue and the stage in the soil are not hit.
  • Follow-up: re-spray about 3–5 days after the first spray, to kill new adults emerging from the soil before they begin laying eggs. For citrus, see Citrus aphids, thrips and whitefly.

Whiteflies

  • Common pests: silverleaf whitefly and many other whitefly species with various plant preferences.
  • Identification: tiny, moth-like adults with white-waxed wings. Adults are weak flyers, but they move to new plants or newer leaves. Nymphs look like small, flat scale insects.
  • Life cycle: the hatched nymph moves to select a spot to feed. It then goes through 4 nymph stages over about 4 weeks. The 4th stage does not feed; it changes into an adult. Females live about 4 weeks and lay 20–30 eggs.
  • Where they hide: all stages feed on the undersides of leaves.
  • Crops: brassicas and cucurbits are the most affected (cucumbers, pumpkins, tomatoes, broccoli), but many other crops are attacked, indoors or outdoors.
  • Damage: marked produce and lost photosynthesis. Honeydew goes black with sooty mould. They may spread plant viruses.
  • What a contact spray hits: adults, crawlers and young nymphs, if the underside is actually wet. Eggs and the later, settled stages are much harder. Large infestations curl the leaves, which makes contact harder, so spray early, before leaf distortion.
  • Follow-up: re-spray when young nymphs and adults are visible again. See Spray coverage for whitefly and earwigs.

Leafhoppers (jassids)

  • Identification: adults have four membranous wings; nymphs are a similar shape without wings. They’re called “hoppers”, but they don’t have specialised hopping legs like grasshoppers. They move quickly out of sight around the plant as you walk past.
  • Life cycle: egg to adult in about 1–3 weeks, through 5 nymphal stages, with several generations a year. Single eggs are inserted into slits in leaves and new stems.
  • Crops: a wide crop range: trees, shrubs, field crops and vegetables, indoors or outdoors.
  • Damage: they feed on any part of the plant, sucking sap, and can spread viral and fungal diseases. Generally a minor pest group.
  • What a contact spray hits: nymphs and adults. Eggs in slits can’t be hit.
  • Follow-up: a follow-up spray about a week later kills hatching nymphs before they become adults, mate and lay more eggs.

Caterpillars and cabbage moth

  • Common pests: diamondback moth (the “cabbage moth” of Australian brassicas), cluster caterpillars and armyworms, Helicoverpa and loopers. See Cabbage moths and other caterpillars.
  • Life cycle: moths and butterflies have an erratic flight and lay eggs on chosen crop or pasture leaves. Egg to adult varies widely: from under 20 days for diamondback moth in hot weather to 1–3 months for other species. Most adults live only 3–6 weeks. Cluster moths lay about 300 eggs; others lay fewer. Many pupate in the soil; diamondback moth and loopers pupate in silk on the plant.
  • Where they hide: larvae feed on the leaves and come out of hiding from birds in the evening.
  • Crops: many species attack field crops, tree crops, berries and vegetables, mostly outdoors.
  • Damage: loss of leaf function and unpresentable produce from holes and shredding.
  • What a contact spray hits: the larvae on the plant surface, which do the damage. Larvae that bore inside tissue (nut borers, leaf miners, larvae inside fruit or heads) are not contacted. Eggs are not reliably killed.
  • Follow-up: about 7–14 days later if the next hatch is visible. Spray in the evening, when larvae are exposed.

Earwigs

  • Identification: the European earwig is dark brown, 12–24 mm, with pincers at the rear (curved in males, straighter in females).
  • Where they hide: they are nocturnal. By day they hide in soil, rough bark and leaf litter, and once bunch fruit fills, inside the bunch.
  • Damage: chewed stems (cherries can drop), shallow feeding on ripening fruit, and contamination at picking, on crops such as cherries, tomatoes and grapes.
  • What a contact spray hits: earwigs reached by the droplets, in the bunch or the hide. Earwigs in the soil are not a foliar kill.
  • Follow-up: re-treat when they are back on the plant. Spray at dusk or after dark, when they come out of hiding.

Ants

  • Where they are: on the canopy, farming the honeydew made by aphids and whiteflies.
  • What a contact spray hits: workers on the plant, if the spray hits them. A Py-Bo spray is not a nest treatment.
  • Follow-up: control the aphids and whiteflies making the honeydew, and the ants lose their reason to be there.

Monitoring and beneficials

As the grower, it’s your job to look at your crop more than occasionally. Walk it at least twice a week in warm weather. Look for live insects, yellowed leaves, chewed leaf edges, spotting where insects have fed, honeydew and sooty mould, and frass. Turn leaves over, check flowers and curled leaves, and shake plants over a sheet or tray.

Read the result after each spray. Py-Bo knocks labelled contact pests in minutes. Dead insects mean the droplets hit them. Live ones after the spray has dried were not contacted. Change the application rather than the rate.

Beneficials (ladybirds, lacewings, hoverfly larvae, parasitoids, Orius) eat aphids and thrips. A contact spray kills beneficials it hits, but Py-Bo residues break down within hours of sunlight. If pests have too much of a head start, a contact spray can bring numbers down, and beneficials can go back in a few days later. Use Py-Bo as a knockdown or harvest-close flush, not as a weekly cover spray. See IPM insects and mites: which pests Py-Bo can hit, and which it cannot.

How to spray Py-Bo: rate, withholding and bees

From the Py-Bo label directions for use:

Situation Pests Rate Critical comments
Fruit and vegetable crops, cut flowers and ornamental plants Aphids, ants, cabbage moths and other caterpillars, earwigs, leafhoppers, thrips, whiteflies 1 mL in 1 L of water or 100 mL in 100 L of water Mist or spray to contact the pests when infestation occurs. Thorough coverage of all foliage including undersurfaces is essential.
  • Withholding period: edible plants, do not harvest for 1 day after application. That’s why a follow-up spray close to harvest is practical. See Py-Bo 1-day withholding.
  • Bees: dangerous to bees. Do not spray any plants in flower while bees are foraging. Spray at dusk or after dark, when bees are in the hive.

Pyrethroids are not pyrethrins

The names sound alike, but they are different chemistry. Pyrethroids are man-made insecticides built to last longer on the leaf. Pyrethrins are the natural esters in pyrethrum. Py-Bo pairs them with the PBO synergist, and they break down in sunlight within hours.

Natural pyrethrins don’t have the resistance problems pyrethroids do. Py-Bo is a contact spray, so it has to hit the insect to kill it. If you’re not getting the kill rate you want, change the spray application, direction and droplet size. That’s what makes the difference.

Where Py-Bo is registered: three situations

The Py-Bo label covers three situations, each with its own pests and rate:

  • Fruit and vegetable crops, cut flowers and ornamental plants: aphids, ants, cabbage moths and other caterpillars, earwigs, leafhoppers, thrips and whiteflies. 1 mL in 1 L of water (100 mL in 100 L). Mist or spray to contact the pests when infestation occurs, with thorough coverage of all foliage including undersurfaces.
  • Buildings: domestic, commercial, industrial and public buildings (including food processing, shops, factories, hotels, shipping containers, offices, schools, storerooms, warehouses, hospitals and barracks), plus agricultural buildings such as storage sheds, milking sheds, other high-density animal production sheds, barns, kennels and stables. Mosquitoes, flies, midges, ants, silverfish, moths, cockroaches, grain weevils, spiders, earwigs, beetles and other flying insects. Surface spray at 60–80 mL per 100 m², or space mist or fog at 18 mL per 1,000 m³. Use regularly to kill emerging insects before they can reinfest or spread.
  • Outdoors: adult mosquitoes, midges, flies and other flying insects. 250 mL per hectare, diluted with water or oil and applied through misting or fogging equipment.

Always read the label on the pack and follow the rate and directions for your situation.

More reading

Buy Py-Bo natural pyrethrum

Py-Bo comes in 250 mL, 1 L, 5 L and 20 L. At 1 mL/L, 1 L makes about 1,000 L of spray, enough for a first spray and a follow-up across a good-sized block.

Buy Py-Bo online, or ask at Nutrien Ag, E.E. Muir, Elders, Lindsay Rural or Fernland. Questions: Freecall 1800 12345 7.

Always read and follow the current APVMA-approved label. The label is the law.