Sulfur: what it kills and what it harms
Sulfur is mainly a fungicide against powdery mildew, rust and leaf spot, and it also kills mites. It is one of the oldest organic options, and its home-garden rules are about the plants rather than the bugs. Do not use it when temperatures are near or above 90 °F, and keep it at least 2 weeks away from an oil spray (some labels say 4 weeks). It burns some squash, melon, grape and fruit varieties. For beneficials it is middling: UC IPM rates the wettable form low to medium, sulfur dust is harder on them, and in field trials repeated sulfur sprays went with fewer predatory mites and more spider mites.
Also sold or listed as: sulphur, wettable sulfur, garden sulfur, Bonide Sulfur Plant Fungicide, Safer Brand Garden Fungicide.
At a glance
- Active
- Elemental sulfur (wettable or micronized powder, dust, or liquid)
- Residue
- Short (hours to days) for wettable sulfur; days to 2 weeks for dust
- Caution
- 5 of 5 beneficials
What it works on
- Powdery mildew, rust and leaf spotThe main use. It works as a protectant: spray it before the disease appears or at the first sign, and repeat. UC IPM prefers wettable sulfurs made with soap-like surfactants over dusts.
- Spider mitesListed as "red spider" on beans, peas, currants and fruit trees (Bonide). It can also backfire: in hop yards, repeated sulfur sprays were followed by 1.4–3.3 times more spider mites in summer (Gent et al. 2009).
- Tomato russet miteUC IPM lists mined sulfur dust or sprays as the organically acceptable treatment on tomatoes.
- Broad miteUC IPM lists wettable sulfur among the potentially effective home-garden miticides for broad mite, with horticultural oil, insecticidal soap and neem oil.
- Citrus mites, thrips and scaleOn the Bonide label for citrus: rust mite, two-spotted mite, citrus red spider (mite), thrips, and soft, red, yellow, purple, black and citricola scales.
- ChiggersBonide dust at about 2 lb per 1,000 sq ft of yard, repeated weekly (not in California).
Effect on beneficials
- Phytoseiulus persimilisUC IPM rates wettable sulfur low to medium and sulfur dust medium for predatory mites (→ caution). The UC cucurbit table rates sulfur low for pesticide-resistant predatory mite strains but high for native strains. These ratings are mostly based on the western predatory mite. In that species, dry flowable sulfur did not kill adults, but its residues were highly toxic to hatching larvae and strongly repellent to adults. In Washington hop yards, sulfur-sprayed plots had 10 times fewer predatory mites. — UC IPM floriculture (2022) and cucurbit (2016) tables; Beers et al. 2009, J. Econ. Entomol. 102:324; Gent et al. 2009Caution — moderate, 25–75 %
- Amblyseius cucumerisNo cucumeris-specific data found. UC IPM rates predatory mites low to medium for wettable sulfur and medium for dust in greenhouse and nursery crops, and the cucurbit table ranges from low (resistant strains) to high (native strains), so the rating is caution. Residue toxicity to young predatory mites and repellency are reported for another phytoseiid (Beers et al. 2009). — UC IPM floriculture (2022) and cucurbit (2016) tables; Beers et al. 2009Caution — moderate, 25–75 %
- Aphidius colemaniThe UC IPM tables disagree. The greenhouse and nursery table rates parasites low for wettable sulfur and medium for dust, while the tomato and cucurbit tables rate sulfur high for parasites. Caution covers that range. No Aphidius-specific trial was found. — UC IPM floriculture (2022), tomato (2016) and cucurbit (2016) tablesCaution — moderate, 25–75 %
- Encarsia formosaNo Encarsia-specific data found. UC IPM rates parasites anywhere from low (wettable sulfur, greenhouse table) to high (tomato and cucurbit tables), so the rating is caution. — UC IPM floriculture, tomato and cucurbit tablesCaution — moderate, 25–75 %
- Chrysoperla carneaUC IPM rates wettable sulfur low and sulfur dust low to medium for predators other than mites in greenhouse and nursery crops. The tomato table rates general predators medium and the cucurbit table medium to low (→ caution). — UC IPM floriculture, tomato and cucurbit 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
Sulfur kills fungi on contact. Exactly how is not settled; the main theory is that it gets into fungal cells and disrupts respiration. It also kills mites and some insects that touch or eat it (NPIC). It does not cure an established infection well, so treat early.
It comes as a fine powder that can be dusted on or mixed with water (Bonide, 90% sulfur), or as a ready-mixed liquid (Safer Brand Garden Fungicide, 0.4% in the ready-to-use spray and 12% in the concentrate). UC IPM calls sulfur dust harder to use, irritating to skin and eyes, and limited in the plants it suits.
Heat: sulfur burns leaves in hot weather. UC IPM says not to apply it when the air is near or above 90 °F. The Safer label sets the limit lower, at 85 °F. The Bonide label says to avoid high temperatures and to use its lower rates above 90 °F.
Oil: sulfur and oil together injure plants. The gap between them varies by source. UC IPM's powdery mildew guide and the Bonide label say 2 weeks (Bonide says 3 weeks on citrus). UC IPM's spider mite guide says 30 days, and the Safer label says at least 4 weeks after an oil spray. Neem oil counts as an oil. Follow the label in your hand, and if in doubt use the longer gap.
Using it
- Products
- Bonide Sulfur Plant Fungicide, a micronized spray or dust (90% sulfur, EPA Reg. 4-62). Safer Brand Garden Fungicide, a concentrate (12%, EPA Reg. 42697-37) or ready-to-use spray (0.4%, EPA Reg. 42697-17).
- Rate
- Bonide: 1–3 Tbsp per gallon depending on the crop, for example 1½–3 level Tbsp on beans and peas, and 2–2¼ level Tbsp on roses and ornamentals. Safer concentrate: 4 Tbsp (2 fl oz) per gallon for powdery mildew, and 8 Tbsp (1 part in 30) per gallon for black spot, leaf spot and rust and in home greenhouses.
- Interval
- Every 7–10 days on beans and peas, and every 5–10 days and after rain on roses (Bonide). Otherwise, repeat as needed.
- Days to harvest
- Bonide allows use up to the day of harvest on the listed fruit and vegetables. Safer allows up to the day before harvest on beans, peas and strawberries, and not within 21 days of harvest on wine grapes.
- Re-entry
- Bonide: do not enter treated areas within 24 hours without long sleeves, long pants, shoes and socks. Safer: avoid contact with plants until the spray has dried.
Cautions
- Heat and oil
- No sulfur near or above 90 °F (85 °F on the Safer label). No sulfur within 2–4 weeks of an oil spray, depending on the label, and no oil within 2 weeks of sulfur (UC IPM).
- Sensitive plants
- Sulfur can damage some squash and melon varieties (UC IPM). The labels also warn against McIntosh, Golden Delicious and Jonathan apples, Anjou and Comice pears, Concord and other labrusca grapes, Boston fern, spinach, apricots, filberts, walnuts and viburnum. Do not spray young cucumber, squash, tomato or strawberry plants, and melon leaves are very prone to sulfur burn (Safer). Test on a few plants first.
- Bees
- UC IPM gives sulfur bee precaution III: no bee precaution unless the label requires one. NPIC reports sulfur as practically non-toxic to honey bees, and the home labels carry no bee statement.
- Pets
- Sulfur is low in toxicity to people, but animals that eat too much can be poisoned, sometimes fatally (NPIC). The Bonide label says it is harmful if swallowed, inhaled or absorbed through the skin, although it is also labelled as a flea and tick dust for dogs outside California.
- Fish
- The Bonide label says it is toxic to fish, though NPIC reports sulfur as practically non-toxic to bluegill, trout and water fleas. Keep it out of drains and ponds either way.
- Fire and drift
- Sulfur dust hanging in the air ignites easily, so keep sparks and cigarettes away while dusting (Bonide). Drift can injure nearby sulfur-sensitive plants (NPIC).
Use instead
- Where you have released predatory mites such as Phytoseiulus persimilis, avoid repeated sulfur. UC IPM suggests a soap spray to knock spider mites down before releasing predators. See insecticidal soap.
- For mild or moderate powdery mildew that is already visible, UC IPM rates horticultural or neem oil as better eradicants than sulfur. Never use oil within 2 weeks of sulfur. See horticultural oil.
Other products
Sources
UC IPM Pest Notes: Powdery Mildew on Vegetables, Pub. 7406 (Davis, Gubler & Koike, updated 11/2008)
UC IPM Pest Notes: Spider Mites, Pub. 7405 (Godfrey, updated 12/2011)
UC IPM, Relative toxicities of pesticides used in floriculture and nurseries to natural enemies (2022)
UC IPM, Relative toxicities tables for tomatoes (2016) and cucurbits (2016)
UC IPM Pest Management Guidelines: Tomato, Tomato Russet Mite
Bonide Sulfur Plant Fungicide label, EPA Reg. 4-62 (2021 notification)
Safer Brand Garden Fungicide labels, EPA Reg. 42697-37 (2010) and 42697-17 (2009)
NPIC, Sulfur General Fact Sheet (reviewed 2017)
Beers et al. 2009, J. Econ. Entomol. 102:324–335 (sulfur products and orchard mites)
Gent et al. 2009, J. Econ. Entomol. 102:274–286 (mildew fungicides, spider mites and predators in hops)
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.