Walk into a rural store and you will see several bottles labelled “pyrethrum.” Some are commercial crop sprays. Some are fogging or multi-use concentrates. Some are garden lines that look related to the commercial packs. The front of the bottle does not always make the difference obvious.
This guide is for growers, farm-store staff, and anyone comparing concentrates at the counter. It explains what g/L pyrethrins means, how the common Australian strength tiers sit next to each other, and why mix rate (not just the number on the label) decides cost-in-use. Always read the current APVMA-approved label on the bottle in your hand. The label is the law.
Py-Bo is Pestech’s natural pyrethrum concentrate: 80 g/L pyrethrins + 320 g/L piperonyl butoxide (PBO), APVMA 53738. Typical horticultural mix is 1 mL per litre of water (check the current label). It is a contact spray with a 1-day withholding period on labelled edible crops. Packs: 250 mL / 1 L / 5 L / 20 L.
Related: Py-Bo product page · 1-day withholding explained · Py-Bo hub
What “pyrethrum concentrate” means on an Australian shelf
On an Australian agricultural chemical label, pyrethrum usually means natural pyrethrins extracted from Chrysanthemum cinerariaefolium (the daisy), often formulated with piperonyl butoxide (PBO) as a synergist. The strength line that matters for shelf comparison is:
- g/L pyrethrins — how much active insecticidal ester is in each litre of concentrate
- g/L PBO — how much synergist sits alongside those pyrethrins
- APVMA number — the registered product identity (Py-Bo is 53738)
A higher g/L figure does not automatically mean “stronger spray on the leaf.” It means more active in the bottle. What you put on the crop is decided by the mix rate on that product’s label (for example 1 mL/L vs a different rate on another pack). Two concentrates can both say “pyrethrum” and still be aimed at different jobs: commercial fruit and veg contact spray, fogging or multi-use flying-insect work, or home-garden lines.
Before you buy, check three things on the label in front of you:
- g/L pyrethrins (and PBO if listed)
- Approved uses and pests for your crop or situation
- Mix rate, withholding period, and any bee or re-entry directions
If those three do not match the job you have, it is the wrong bottle — even if the brand name feels familiar.
Strength tiers at a glance: ~80 · ~75 · ~40 · ~13 g/L
Australian farm-store and digital shelves commonly group natural pyrethrum concentrates into four strength bands. Use the tier, not the marketing headline, when you compare.
| Tier (approx.) | Typical role on the shelf | What to watch |
|---|---|---|
| ~80 g/L pyrethrins | Commercial horticultural EC (crop contact spray) | Highest concentrate band; Py-Bo sits here at 80 g/L + 320 g/L PBO |
| ~75 g/L pyrethrins | Commercial peers for veg / ornamentals contact spray | Close band; still check mix rate, solvent claims, and labelled pests |
| ~40 g/L pyrethrins | Fogging / multi-use lookalikes (surface + mist / fog narratives) | Often sold beside crop sprays; job and label may differ from a pure hort EC |
| ~13 g/L pyrethrins | Garden / home lines | Easy to confuse with commercial solvent-free packs if you only read “pyrethrum” |
Py-Bo at 80 g/L is the strongest concentrate in this comparison. You will not find a stronger pyrethrum concentrate. That claim is about grams per litre in the bottle, not a promise that every other product fails on every pest.
Do not treat “high concentration” marketing as a substitute for the g/L line. A 40 g/L fogging-style pack can still be described as strong relative to a 13 g/L garden line, while sitting well below commercial ~75–80 g/L crop concentrates. Read the number.
Garden ~13 g/L lines are the ones most often confused with commercial solvent-free concentrates when they share a brand family or sit in the same aisle. If your job is labelled fruit, vegetables, cut flowers or ornamentals at a commercial mix, confirm you have picked the commercial tier — not the home-garden pack.
How mix rate and spray volume decide cost-in-use
Shelf price per litre of concentrate is a weak way to compare products. What matters is how much spray you get from a litre of concentrate at the labelled rate, and whether that rate is the one you will actually use.
Simple maths only (no competitor prices):
- At 1 mL/L, 1 L of concentrate makes about 1,000 L of spray.
- At 1 mL/L, 5 L of concentrate makes about 5,000 L of spray.
- At 1 mL/L, 250 mL of concentrate makes about 250 L of spray.
- At 1 mL/L, 20 L of concentrate makes about 20,000 L of spray.
- If a label calls for 2 mL/L, the same 1 L of concentrate only makes about 500 L of spray — half the tank volume for the same bottle.
- Garden rates are often written differently (for example per garden sprayer fill). Convert everything to mL of concentrate per litre of water before you compare cost-in-use.
Py-Bo’s typical horticultural rate is 1 mL/L (always check the current label). That is why pack size maps cleanly to tank volume for growers who already spray at that rate.
Cost-in-use checklist at the counter:
- Note g/L pyrethrins on each bottle.
- Note the labelled mix rate for your crop or situation.
- Calculate litres of spray per litre of concentrate.
- Only then compare price per litre of finished spray — not price per litre of neat concentrate alone.
Two bottles can sit in the same ~75–80 g/L band and still work out differently if one label sends you to 1 mL/L and another to a higher rate for the same job. The mix rate is not optional fine print.
Contact spray basics: coverage, dusk/UV, 1-day WHP, bees
Natural pyrethrum concentrates used as hort sprays are contact products. Droplets have to hit the insect. They are not systemic. They are not baits. Missed undersides, tips, and the far side of the row mean live insects tomorrow.
Coverage. Walk the spray pattern the way you walk the pest. Aphids, thrips, whiteflies, leafhoppers, caterpillars, earwigs and ants named on the Py-Bo label only die where the spray reaches them. Eggs, pupae, and insects under leaves you skipped are still in the block.
Dusk and UV. Pyrethrins break down in sunlight. Short residue is the point for harvest-close work — and the reason you often spray after sundown when you can. UV has not already stripped the deposit, contact on the insect is better, and bee risk is lower than a daylight spray on open flowers.
1-day withholding on labelled edibles. On Py-Bo, the withholding period for labelled edible crops is one day: spray today, pick tomorrow (where the label allows). That is a legal harvest gap, not a week of residual “protection.” Read the 1-day withholding article for the grower-facing detail. Always confirm the current label for your crop.
Bees. Do not spray plants in flower while bees are foraging. Apply after dark when bees are in the hive. Residues can still keep bees off treated surfaces into the next morning until UV degrades the pyrethrins. Short residue is not the same as “bee-safe in daylight on bloom.”
Named horticultural pests on the Py-Bo label (as stated for labelled fruit and vegetable crops, cut flowers and ornamentals): aphids, ants, cabbage moth and other caterpillars, earwigs, leafhoppers, thrips, whiteflies.
Pyrethroids are not pyrethrins
Resistance talk on the farm often collapses two different chemistries into one word.
- Pyrethroids are synthetic residuals (the “-thrin” family many growers already know). They can sit on the leaf and keep selecting for resistant populations.
- Pyrethrins in a natural pyrethrum concentrate such as Py-Bo are the daisy esters, usually with PBO. They knock down on contact, then UV breaks them down.
Field resistance that wrecks a spray program is typically a pyrethroid story. That is not the same as claiming pyrethrum “has no resistance” or that it will always succeed where a pyrethroid failed. Coverage still decides it: if you do not hit them, they do not die. If a pyrethroid has already failed on the block, that is one reason growers look at natural pyrethrum — not a guarantee.
Matching the job: crop contact spray vs fogging / flying insects
Strength tier and job must match.
Crop contact spray (commercial hort EC). Use when the label covers your fruit, vegetables, cut flowers or ornamentals, and the pest is on the plant (aphids, thrips, whiteflies, caterpillars, leafhoppers, earwigs, ants as named). Py-Bo in the ~80 g/L tier is built for that hort contact job at a typical 1 mL/L mix. Follow the bottle.
Fogging / multi-use / flying-insect narratives. ~40 g/L packs are often sold with fog, mist, surface, mosquito or building-use stories. Those may be the right tool for a labelled fogging or multi-use situation — and the wrong tool if you only needed a commercial crop spray. Do not invent rates or situations this article does not cover. Follow the label on the bottle in your hand.
Garden / home lines (~13 g/L). Fine for labelled home-garden use. Not a silent substitute for a commercial concentrate if your mix maths and pack size assume an ~75–80 g/L hort EC.
If you are unsure which tier you are holding, read g/L, APVMA number, approved situations, and mix rate before the tank fill — not after.
Where to buy / ask
Buy Py-Bo (250 mL / 1 L / 5 L / 20 L) from Pestech:
Py-Bo Natural Pyrethrum Concentrate
Or ask at Nutrien Ag, E.E. Muir, Elders, Lindsay Rural, Fernland (and Pestech). Current pack pricing lives on the product page — it can move, so check there rather than memorising an old catalogue line.
More grower context: Py-Bo hub · Pyrethrum 1-day withholding
Always read the current APVMA-approved label and SDS before use.