Insecticidal Soap vs Neem Oil vs Horticultural Oil
Quick answer
Use soap for aphids, whiteflies and mites you can wet directly; horticultural oil for scale, mites and dormant fruit-tree sprays; neem to stop young insects feeding; and Bt or spinosad for small caterpillars. Check each one’s bee rating, and use any product as the label directs.
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Insecticidal soap, horticultural oil and neem all work best on small, soft-bodied pests and young stages, and only when they touch the pest. Bt and spinosad are the caterpillar options. None is risk-free: check the bee rating before you spray, and use any product as the label directs.
Use any product as the label directsUMN Extension: “Always follow the pesticide label directions ... Be sure that the plant you wish to treat is listed on the label ... And observe the number of days between pesticide application and when you can harvest your crop. Remember, the label is the law.”
Side by side
| Product | What it controls | How it works and limits | Bee rating (UC IPM) | Cautions | Organic status |
|---|---|---|---|---|---|
| Insecticidal soap | “aphids, whiteflies, mites, and other soft-bodied insects” (UC IPM) | “complete coverage of pests is needed and sometimes a repeat application” | III | Not on “water-stressed plants or when the temperature exceeds 90°F”; test a few leaves first | Listed in 7 CFR 205.601: “Soaps, insecticidal” |
| Horticultural oil | “aphids, whiteflies, mealybugs, scale insects, spider mites, psyllids, and thrips” (UC IPM) | UNR: “The oil has no effect after it has dried.” | II (mineral oil) | Not above 90°F; not within 30 days of sulfur (UNR) | Listed in 7 CFR 205.601: narrow range oils as dormant, suffocating, and summer oils |
| Neem (azadirachtin) | UNR: “It reduces insect feeding, growth and egg laying ... effective against immature stages” | UC IPM: “has limited effectiveness but low toxicity to nontargets” | II | UNR: “slightly toxic to fish” | Check that the product is OMRI-listed or approved by your organic certifier. |
| Bt (kurstaki) | “controls leaf-feeding caterpillars” (UC IPM) | Must be eaten; works best on small caterpillars (UMN) | III | Caterpillars only | UC IPM: Bt sprays and the Entrust formulation of spinosad “are acceptable for use on an organically grown crop” (UC IPM). Check the product label. |
| Spinosad | “caterpillars, leafminers, thrips, and several other insects” (UC IPM) | Contact and ingestion | II | UC IPM: “it can also harm some beneficial insects”; Colorado potato beetle resistance reported (UMN) | UC IPM: Bt sprays and the Entrust formulation of spinosad “are acceptable for use on an organically grown crop” (UC IPM). Check the product label. |
Sources: UC IPM, Less Toxic Insecticides; UC IPM, corn earworm (organic acceptability); UC IPM, Aphids; UNR Extension, Horticultural Oils; UMN Extension, caterpillars on cole crops; UC IPM bee precaution ratings; eCFR 7 CFR 205.601.
When to pick soap
For aphids, whiteflies and mites, when you can wet every pest. UC IPM says soaps and oils “leave no toxic residue so they don't kill natural enemies that migrate in after the spray” (UC IPM), which is also why a repeat spray is often needed.
When to pick horticultural oil
For scale, mites and overwintering eggs on fruit trees. Oregon State says dormant oil goes on “in January or February ... when temperatures are above freezing and under dry conditions” (Oregon State). Keep oil and sulfur apart: UNR says “Oils cannot be combined with sulfur products or sprayed within 30 days of a sulfur application.”
When to pick neem
For young insects you want to stop feeding, such as squash bug nymphs (UMD) or Japanese beetles in small numbers (UMN). UNR says it is low risk to bees “if applied late evening or early morning when bees are inactive”.
Bt and spinosad for caterpillars
Bt only works when caterpillars eat it, so cover the leaves and spray while they’re small (UMN). Spinosad also kills on contact and reaches more pests, but it is bee rating II and “it can also harm some beneficial insects” (UC IPM), so spray outside bloom or after sunset where the label allows.
A note on copper
Copper fungicides are preventive (Rutgers: “Copper-based fungicides are preventative and should be used prior to disease infection”, Rutgers FS1315). Cornell warns copper “can accumulate in soil when used intensively over many years” (Cornell), and the organic rule requires use “in a manner that minimizes accumulation in the soil” (7 CFR 205.601).
See which pests each one fits on organic pest control for vegetable gardens, or browse the Organic gardening hub.
Frequently asked questions
Is neem oil better than insecticidal soap?
They do different jobs. Soap kills soft-bodied insects such as aphids, whiteflies and mites on contact (UC IPM). Neem reduces feeding, growth and egg laying and works best on immature insects (UNR). Soap is bee rating III and neem is II, so spray neem only in the evening or early morning when bees aren't active, and use either as the label directs.
Can I spray soap or oil in hot weather?
No. UC IPM says not to use soaps or oils on water-stressed plants or when the temperature exceeds 90°F.
Does Bt hurt bees?
UC IPM gives Bt kurstaki its lowest bee precaution rating (III), and UMN Extension says caterpillars must eat it for it to work. Use it as the label directs.
Are neem, Bt and spinosad allowed in organic gardening?
UC IPM says Bt sprays and the Entrust formulation of spinosad are acceptable for use on an organically grown crop; check the product label. For neem, check that the product is OMRI-listed or approved by your organic certifier. Insecticidal soaps and horticultural oils are listed in 7 CFR 205.601.
Sources
- University of California Agriculture and Natural Resources (UC ANR): Corn earworm; UC IPM, Less Toxic Insecticides; UC IPM, Aphids; UC IPM bee precaution ratings
- University of Nevada, Reno Extension: UNR Extension, Horticultural Oils
- University of Minnesota Extension: UMN Extension, caterpillars on cole crops
- Electronic Code of Federal Regulations (eCFR), 7 CFR 205.601: eCFR 7 CFR 205.601
- Oregon State University Extension: Em 9452 pest management schedules fruit trees eastern oregon
- Rutgers NJAES Cooperative Extension: Rutgers FS1315
- Cornell University Vegetable Program: Copper fungicides for organic disease management in vegetables