Insecticidal soap: what it kills and what it harms
Insecticidal soap kills soft-bodied pests such as aphids, mites, whiteflies, mealybugs, young scale and thrips, but only the ones the spray wets. Once dry it does nothing. That makes it one of the gentlest sprays for beneficials that arrive afterwards, though it can kill small beneficials it hits directly. Use a labelled product: dish soap is not the same thing, and it can burn plants.
Also sold or listed as: fatty acids, potassium salts, potassium laurate, soap salts.
At a glance
- Active
- Potassium salts of fatty acids
- Residue
- None once dry. It kills on contact only and leaves no active residue (Colorado State; UC IPM rates its duration 'short' to 'short to none').
- Caution
- 6 of 7 beneficials
- Safe
- 1 of 7 beneficials
What it works on
- AphidsIts best-known use. Aphids inside curled leaves escape it, because the spray has to wet them (Colorado State). The Safer label says to check again after two days and spray again if needed.
- Spider mitesOn the label. Colorado State says repeat sprays every 4 to 7 days may be needed for spider mites. The label says to time a second spray to catch newly hatched young.
- WhitefliesOn the label for vegetables, herbs and fruit.
- MealybugsOn the label. A monthly soil drench of 1–2 tbsp of concentrate per quart of tepid water reduces root mealybugs in houseplants.
- Scale crawlersOnly the young, mobile crawler stage. Spray to wet the bark when crawlers are active.
- ThripsOn the label, including blossom thrips on African violets. Spray the blooms directly.
- EarwigsOn the label. Disturb their hiding places and spray the earwigs directly.
- Not caterpillars or beetlesColorado State says larger insects such as caterpillars, sawflies and beetle larvae are generally immune. The label allows a stronger 4 fl oz per gallon mix for young tent caterpillars on their tent.
Effect on beneficials
- Phytoseiulus persimilisIn a lab contact test, insecticidal soap was 'very toxic' to P. persimilis adults. UC IPM's floriculture table rates its effect on predatory mites low, and UC IPM lists soap as having direct but no residual toxicity. It kills mites it wets but not those released after it dries, so this is rated caution. Colorado State says beneficial mites are affected as well as pest mites. — Bostanian & Akalach 2006, Pest Manag Sci 62:334; UC IPM floriculture table (2022)Caution — moderate, 25–75 %
- Amblyseius cucumerisWe found no trial on A. cucumeris. Colorado State says soap affects beneficial mites as well as pest mites, and UC IPM's floriculture table rates predatory mites low. Rated caution as a direct-contact risk, like P. persimilis. — Colorado State fact sheet 5.547; UC IPM floriculture table (2022)Caution — moderate, 25–75 %
- Aphidius colemaniIn a lab test, insecticidal soap killed half of adult wasps within 24 hours at 2.75 g/L and all of them at 17.5 g/L. Wasp larvae developing inside treated aphids were unharmed, though females laid fewer eggs in treated aphids. UC IPM rates parasites low (floriculture) to moderate (tomato). A related wasp, A. rhopalosiphi, was unharmed by soap residues (Jansen et al. 2010). Rated caution. — Tremblay et al. 2008, Pest Manag Sci 64:249; UC IPM floriculture (2022) and tomato relative toxicity tablesCaution — moderate, 25–75 %
- Encarsia formosaResidues from poinsettia cuttings dipped in 0.5 % soap plus Beauveria had little effect on Encarsia survival. A direct spray was not tested. UC IPM rates parasites low to moderate. Rated caution because a direct spray is still a contact risk. — Buitenhuis et al. 2016, Insects 7:48; UC IPM floriculture (2022) and tomato relative toxicity tablesCaution — moderate, 25–75 %
- Chrysoperla carneaUC IPM rates general predators low (floriculture) to moderate (tomato). Colorado State says the larval stages of larger insects may be susceptible. We found no C. carnea trial. Rated caution. — UC IPM floriculture (2022) and tomato relative toxicity tables; Colorado State fact sheet 5.547Caution — moderate, 25–75 %
- Orius insidiosusIn a lab contact test, insecticidal soap was 'very toxic' to Orius nymphs. A 2025 lab study exposed eggs, nymphs and adults to soap at the high vegetable label rate and at a tenth of it, and found some lethal and sublethal effects. Rated caution because it kills on contact but leaves no lasting residue. — Bostanian & Akalach 2006; Gaire & Amarasekare 2025, J Econ Entomol 118:2195Caution — moderate, 25–75 %
- Samurai waspFemales kept for 7 days on dried potassium-salt residue at the field rate (20 ml/L): 20.1 % ± 9.2 mortality, not different from the untreated control at day 4. This was a residue test; a direct spray was not tested. — Chierici et al. 2025, Sci Rep 15:4622Safe — low toxicity, under 25 % effect
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
Insecticidal soaps are potassium salts of fatty acids. They damage an insect's cell membranes, so it dries out fast. They may also strip the protective wax from some insects (Colorado State).
It works only as a contact spray. It has to wet the insect, and once it dries it has no effect (Colorado State; Clemson). That is its weakness, since you must cover the undersides of leaves and repeat. It is also why UC IPM puts soaps among the least-toxic choices for natural enemies: a dry leaf is safe for beneficials that arrive afterwards.
It still kills small, soft beneficials that the spray hits, predatory mites among them (UC IPM: direct toxicity yes, residual no). Large adult flying insects such as bees and ladybirds are generally not affected, but larvae may be (Colorado State).
Using it
- Rate
- 2.5 fl oz (5 tbsp) of concentrate per gallon of water, a 1:50 mix, for indoor plants, outdoor flowers, vegetables and fruit. Use soft water where possible, and mix fresh (Safer Insect Killing Soap Concentrate, EPA Reg. 42697-1). Ready-to-use sprays come pre-mixed.
- How often
- Spray when pests appear, and wet every infested surface. Indoors, repeat weekly (every 7 to 10 days) as needed, up to three times; on outdoor vegetables, weekly to fortnightly, up to three times. Do not make repeated sprays at short intervals without thoroughly rinsing the leaves (label).
- Heat
- Do not spray above 90°F (32°C) or in the heat of the day. Spray cucumbers at night or in the coolest part of the day (label; UC IPM).
- Houseplants
- Labelled for indoor plants at the same rate. Clemson says a soap spray can often clear an infestation in its early stages. Test first on the sensitive plants listed below.
- Harvest and re-entry
- May be used up to and including the day of harvest (label). The agricultural product M-Pede carries a 12-hour restricted-entry interval. The home label gives none.
Cautions
- Plant injury
- Do not spray new transplants, fresh cuttings or drought-stressed plants. The label names bleeding heart, gardenia, jade plant, lantana and sweet peas as plants not to spray, and crown of thorns among houseplants. Some varieties of azaleas, begonias, camellias, fuchsias and impatiens are soap-sensitive. Test first on euphorbias, dracaena, delicate ferns, dieffenbachia, ornamental ivies, palms, succulents and chrysanthemums. On trees, avoid chestnut, Japanese maple, mountain ash and Colorado blue spruce.
- Fruit marking
- It may mark some apple and pear varieties, spot nectarines and remove the waxy bloom from plums and spruce (label).
- Homemade dish-soap sprays
- Colorado State advises against them. Dish soaps contain strong detergents that can injure plants, damage soil and contaminate waterways. Homemade mixes are not consistently made or tested, so there is no evidence they work. Household soaps are also not exempt minimum-risk pesticides, so using them this way is of questionable legality.
- Bees
- The home label we read carries no pollinator statement, and UC IPM gives soap no bee precaution (rating III) beyond the label. The label still says to avoid spraying fruit and nut crops while blossoms are present.
- Fish
- 'This product may be hazardous to aquatic invertebrates.' Do not apply it directly to water, and do not contaminate water when cleaning equipment or disposing of leftover spray (label).
- Eyes
- The concentrate carries a WARNING signal word, because it causes substantial but temporary eye injury. Wear eye protection when mixing.
Use instead
- Spider mites under glass or indoors: release Phytoseiulus persimilis. If you spray soap first, wait until it has dried.
- Aphids outdoors: leave room for hoverflies and ladybugs. In a greenhouse, use Aphidius colemani.
- Scale and overwintering eggs on dormant trees: horticultural oil.
- Caterpillars: Bt kurstaki. Soap does little to them.
Other products
Sources
Colorado State University Extension, Insect Control: Insecticidal Soap, fact sheet 5.547
EPA label, Safer Insect Killing Soap Concentrate, EPA Reg. 42697-1 (2009 master label)
EPA label, M-Pede (Gowan), EPA Reg. 10163-324, 21 Jan 2021
UC IPM, Relative toxicities of pesticides used in floriculture to natural enemies and honey bees (2022)
UC IPM, Relative toxicities of insecticides used in tomatoes to natural enemies and honey bees
UC IPM Pest Notes: Biological Control and Natural Enemies of Invertebrates (toxicity table)
UC IPM Pest Notes: Aphids, UC ANR Pub. 7404
Clemson HGIC 2252, Common Houseplant Insects & Related Pests (rev. 2021)
Tremblay et al. 2008, Insecticidal soap and Aphidius colemani. Pest Manag Sci 64:249
Bostanian & Akalach 2006, Six insecticides on P. persimilis and Orius nymphs. Pest Manag Sci 62:334
Jansen et al. 2010, Organic insecticides on four aphid natural enemies. Pest Manag Sci 66:650
Buitenhuis et al. 2016, Biopesticide dips for Bemisia on poinsettia cuttings. Insects 7:48
Gaire & Amarasekare 2025, Low-risk insecticides and Orius insidiosus. J Econ Entomol 118:2195
Chierici et al. 2025, Natural products vs Halyomorpha halys and Trissolcus japonicus. Sci Rep 15:4622
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.