Pyrethrin: what it kills and what it harms
Pyrethrins are the natural insecticide in pyrethrum daisies. They are a broad-spectrum contact killer that knocks insects down fast and breaks down in sunlight within days. They are not the same as pyrethroids such as bifenthrin and permethrin, which are man-made copies built to last much longer and are far harder on beneficials. Many garden sprays add piperonyl butoxide (PBO), which makes pyrethrins stronger and makes them worse for predators. Pyrethrins are highly toxic to bees and fish on contact. For released beneficials, UC IPM rates them medium to high for parasitic wasps and medium for predatory mites, with only a short residue.
Also sold or listed as: pyrethrins, pyrethrum, PyGanic, Bonide Pyrethrin Garden Insect Spray, Pyrenone.
At a glance
- Active
- Pyrethrins from chrysanthemum (pyrethrum) flowers, alone or with the synergist piperonyl butoxide (PBO)
- Residue
- Short: hours to days; under 3% left on leaves after 5 days
- Caution
- 5 of 5 beneficials
What it works on
- AphidsOn both labels. UC IPM notes that soap-and-pyrethrin mixes give slightly more knockdown than soap alone.
- Flea beetlesListed on eggplant and cole crops (Bonide).
- Cucumber beetlesListed on the PyGanic Gardening label; Bonide lists the 12-spotted (spotted) cucumber beetle on beans.
- Harlequin and stink bugsHarlequin bug and stink bug are on both labels (Bonide lists them on cole crops).
- Mexican bean beetleListed on beans (Bonide).
- LeafhoppersListed on beans and other crops.
- CaterpillarsCabbage looper, imported cabbageworm and diamondback moth larvae are listed, but Bt kurstaki does the same job with little or no harm to lacewings, predatory beetles or parasitic wasps (NPIC).
Effect on beneficials
- Aphidius colemaniThe UC IPM tables disagree. The greenhouse and nursery table rates parasites high for pyrethrins with or without PBO, while the cucurbit and cole-crop tables rate them medium. Caution covers that range (M–H). In an Italian trial, a pyrethrin spray did not reduce A. colemani emergence from mummies; adult wasps were not tested. — UC IPM floriculture (2022), cucurbit (2016) and cole-crop (2020) tables; Lami et al. 2024, Insects 15:556Caution — moderate, 25–75 %
- Encarsia formosaNo Encarsia-specific data found. UC IPM rates parasites high for pyrethrins in greenhouse and nursery crops and medium in the cucurbit and cole-crop tables (M–H → caution). Residues are short-lived. — UC IPM floriculture, cucurbit and cole-crop tablesCaution — moderate, 25–75 %
- Phytoseiulus persimilisUC IPM rates pyrethrins medium for predatory mites, with or without PBO (M → caution). That rating is mostly from the western predatory mite. Impact is short, lasting hours to days. — UC IPM floriculture table (2022)Caution — moderate, 25–75 %
- Amblyseius cucumerisNo cucumeris-specific data found. UC IPM rates predatory mites medium for pyrethrins and for pyrethrins with PBO (M → caution). — UC IPM floriculture table (2022)Caution — moderate, 25–75 %
- Chrysoperla carneaUC IPM rates pyrethrins medium for predators other than mites (M → caution), and the cucurbit and cole-crop tables agree. Adding PBO raises the greenhouse rating to high, so choose a product without PBO if lacewings matter. — UC IPM floriculture, cucurbit and cole-crop tablesCaution — moderate, 25–75 %
No data never means safe: treat an unrated pairing as caution and try it on a small area first. See every product side by side →
How it works
Pyrethrins are six related compounds extracted from chrysanthemum (pyrethrum) flowers. They excite the insect nervous system, and insects that touch or eat them are quickly paralysed and die (NPIC). They kill mainly on contact, so coverage matters more than residue.
They break down fast. In sunlight, pyrethrin I (one of the six) has a half-life of about 13 hours on soil, and less than 3% remained on potato and tomato leaves after 5 days (NPIC). That short life is why UC IPM rates their impact on natural enemies as short.
Pyrethrins and pyrethroids are not the same thing. Pyrethroids (bifenthrin, permethrin, lambda-cyhalothrin, cyfluthrin) are man-made chemicals modelled on pyrethrins to last longer (NPIC). UC IPM rates bifenthrin and lambda-cyhalothrin high for predatory mites, predators and parasites, and bifenthrin's impact as long-lasting. Some pyrethroids are also a known trigger for spider mite outbreaks, because they kill mite predators (UC IPM). Check the active ingredient, not the word "pyrethrin" on the front of the bottle.
PBO (piperonyl butoxide) is a synergist. It is not meant to kill insects on its own. It blocks some of the enzymes insects use to break insecticides down, so insects are less likely to recover from a pyrethrin spray (NPIC). The Bonide concentrate is 1% pyrethrins with 10% PBO. PyGanic is pyrethrins alone, labelled for organic gardening. With PBO added, UC IPM's rating for predators other than mites rises from medium to high.
Using it
- Products
- PyGanic Gardening (1.4% pyrethrins, no PBO; EPA Reg. 1021-1771). Bonide Pyrethrin Garden Insect Spray Concentrate, also sold as Pyrenone Garden Spray (1% pyrethrins + 10% PBO; EPA Reg. 4-371).
- Rate
- PyGanic Gardening: 1–1.4 fl oz per gallon of water per 1,000 sq ft, or 1½–2 tsp in a 32 oz spray bottle to cover 250 sq ft. Bonide: 1.5 fl oz (3 Tbsp) per gallon, and no more than 1 gallon of spray per 1,000 sq ft outdoors.
- Interval
- Bonide: no more than 10 sprays a season, and not within 3 days of the last one except under extreme pest pressure, and even then not within 24 hours. In April 2026, EPA approved removing the one-day repeat allowance from the PyGanic label.
- Days to harvest
- Bonide says it can be used on vegetables up to the day of harvest. The PyGanic farm label says not to harvest until the spray has dried, and the Gardening label says it can be used on the day of harvest.
- Re-entry
- Both labels: keep adults, children and pets out of the treated area until the spray has dried.
- Timing
- Spray early in the morning or late in the evening, when bees are not foraging (PyGanic). Hit the insects directly.
Cautions
- Bees
- Both labels say: "This product is highly toxic to bees exposed to direct treatment on blooming crops or weeds. Do not apply this product or allow it to drift to blooming crops or weeds while bees are" foraging or actively visiting the area. UC IPM gives pyrethrins bee precaution I, the strictest: never on or drifting onto flowering plants, weeds included. NPIC notes that the slight repellency and rapid breakdown limit some of the risk.
- Fish and water
- Highly to very highly toxic to fish, and very highly toxic to shrimp and aquatic insects (NPIC). The Bonide label says to cover fish aquariums before spraying, and PyGanic forbids spraying on or near water or drains. PBO is also moderately toxic to fish and highly toxic to tadpoles (NPIC).
- Pets and people
- Low toxicity to mammals, but it can irritate skin and airways (NPIC). Bonide: remove pets and birds before spraying, and keep people and pets out until the spray has dried. Both labels carry a CAUTION signal word, and the Bonide concentrate contains petroleum distillate. EPA classifies PBO as a possible human carcinogen; IARC calls it not classifiable (NPIC).
- Plants
- Bonide: use caution on new growth and tender foliage, and do not wet plants to the point of runoff. PyGanic: try it on a few plants and watch for damage for 10 days before spraying widely.
Use instead
- For aphids where parasitic wasps are working: insecticidal soap, which UC IPM rates low for predatory mites, predators and parasites.
- For caterpillars: Bt kurstaki, which targets caterpillars and has little or no toxicity to lacewings, predatory beetles or parasitic wasps (NPIC).
- For Colorado potato beetle larvae: Bt tenebrionis where you can buy it.
- If you must use a pyrethrin, choose one without PBO (such as PyGanic). Never switch to a pyrethroid such as bifenthrin or permethrin expecting the same short residue.
Other products
Sources
NPIC, Pyrethrins General Fact Sheet (reviewed 2014)
NPIC, Piperonyl Butoxide (PBO) General Fact Sheet (reviewed 2017)
UC IPM, Relative toxicities of pesticides used in floriculture and nurseries to natural enemies (2022)
UC IPM, Relative toxicities tables for cucurbits (2016) and cole crops (2020)
UC IPM Pest Notes: Aphids, Pub. 7404 (2013); Spider Mites, Pub. 7405 (2011)
MGK, PyGanic Crop Protection EC 1.4 II / PyGanic Gardening label, EPA Reg. 1021-1771 (amended Apr 2026)
Bonide, Pyrenone / Pyrethrin Garden Insect Spray Concentrate label, EPA Reg. 4-371 (2021 notification)
Lami et al. 2024, Insects 15:556 (natural insecticides, Aphidius colemani and a ladybird)
NPIC, Bacillus thuringiensis General Fact Sheet
Drafted from the cited sources, then checked claim by claim against those sources on 23 September 2026.
Always follow the label. Labels are legally binding; this page is not.