Lime sulphur: applications, rates, phytotoxicity and toxicity

Concentrated lime sulphur solution in a beaker, showing its characteristic deep red colour — Figure 1. Concentrated lime sulphur solution. The **deep red to amber colour** is itself the signature of the active substance: it comes from the long polysulphide chains that form at alkaline pH. As pH falls the chains break, the colour fades and hydrogen sulphide is released, which is why **acidified water destroys the product rather than strengthening it**.

Savvas Pastopoulos, Agronomist MSc, Pastopoulos Agronomics, Neos Mylotopos, Pella, Greece

Lime sulphur is among the oldest plant protection products still in use, and at the same time one of the most misunderstood. It is taken for «mild» because it is permitted in organic farming, when in reality it is caustic, an irritant to the respiratory system, toxic to aquatic organisms and extremely hard on beneficial mites. What follows presents first the applications documented in the international literature and its eight authorised uses in Greece with the official rates. The risks come next, the limits of phytotoxicity, toxicity to the operator, the effects on beneficials and on the environment, and the chemistry and mode of action close the article.

The most dangerous point, before anything else Lime sulphur carries the classification «contact with acids liberates toxic gas» [1]. Under acidic conditions the polysulphide ions readily form hydrogen sulphide (H₂S) [1]. Mixing in a sprayer holding the residue of an acidic product, or rinsing with an acidic cleaner, generates a lethal gas in an enclosed space. This is not a theoretical risk: hydrogen sulphide is the toxicologically relevant compound of the whole product [1].

And one point that is often lost, because it shifts the hazard from the accident to normal use: at the commonly used spray rate of 2%, the dilute solution has a pH of 10 and constantly releases small amounts of toxic hydrogen sulphide vapours [2]. The release therefore does not require an acid; the acid makes it sudden and lethal. In the open field the amount is small, but mixing and loading in a closed shed, in a store or inside a vehicle is a different matter: hydrogen sulphide is heavier than air and collects low down.

8authorised uses in Greece

30days pre-harvest interval on all of them

29 to 32%calcium polysulphide under the FAO specification

58 to 100%mortality of orchard mites, beneficial and phytophagous, within 48 hours, trials in Washington

Contents

Applications documented in the international literature
Postharvest applications
Scale insects, what worked historically, what holds, and what is permitted
Regulatory status and the authorised uses in Greece
Phytotoxicity, where the limits are
Toxicity to the operator
The effect on beneficials
Environment and aquatic organisms
What it is and how it is made
The mode of action
A practical guide to application
The key points
Sources

1. Applications documented in the international literature

1.1 Apple and pear scab

This is the best-documented use. Trials have shown that both preventive and curative applications significantly reduce damage on the leaves and fruit of apple trees inoculated with Venturia inaequalis [2].

The curative action, what sets it apart The ability to act after infection is rare in a substance permitted in organic farming, and it follows from the penetration of the polysulphide into the mycelium [2]. In practice it means that after a wetness event that went uncovered, there is still room to act. The price is set out in the next section: phytotoxicity is frequently observed [2].

1.2 Brown rot of stone fruit

In Greece it is authorised on sweet cherry, apricot, plum and peach against brown rot, at 16 to 24 litres per hectare [5]. The long 30-day pre-harvest interval places it among the early treatments, winter spray, bloom and petal fall, and not in the pre-harvest period.

1.3 Powdery mildew of grapevine

In Greece it is authorised on table and wine varieties, at 10 to 20 litres per hectare [5]. Sulphur and its derivatives are among the oldest materials used against powdery mildew, but the dates circulating for the earliest use differ between sources and are not given here.

1.4 Blossom thinning in apple

This use has nothing to do with plant protection and is not covered by a Greek authorisation, but it is mentioned because it explains the toxicity data in section 8. In Washington State lime sulphur is applied as a blossom thinner at 8% by volume, with the recommended timing at 20% and 80% bloom [6]. That use drove consumption sharply upward: from 3% of the apple acreage treated in 1991 to 33% in 2005 [6].

Sources: 2 5 6

2. Postharvest applications

This field is scientifically mature but not covered by a Greek authorisation. It is set out as documentation of the substance's potential, not as a proposal for application.

Citrus, Smilanick and Sorenson

Immersion of lemons or oranges for 1 to 4 minutes in a warm solution at 40.6 to 43.3 °C containing 0.75% calcium polysulphide reduced green mould caused by Penicillium digitatum by 80% or more [7].
In three successive tests the reduction was 93%, 88% and 81% [7].
Sour rot caused by Geotrichum citri-aurantii was reduced by 35 to 70% [7]. In a laboratory test it fell from 64% in the controls to 35% in the treated fruit [7].
A 3% weight-to-volume solution corresponds to 0.75% active calcium polysulphide [7].

The problem of bath life The sulphide concentration in the solution declines by about 7% every 24 hours, at a rate similar across the whole 25 to 65 °C range, and this is accompanied by the formation of resistant deposits on the equipment [7]. That is, the bath loses strength every day and simultaneously damages the tank.

For stone fruit, postharvest application to peaches has been shown to reduce brown rot by up to 90% [2], while earlier work reported a reduction of about 60% without injury to the fruit [7].

Sources: 2 7

3. Scale insects, what worked historically, what holds, and what is permitted

The question comes up often, because the memory of the old practice is still alive: lime sulphur was the winter material par excellence against scale insects. It was used intensively as a winter treatment for scales, mites and certain diseases in fruit trees, until synthetic organic pesticides displaced it in the 1940s [2].

The mechanism explains why the treatment was a winter one. The toxicity of lime sulphur to insects and mites is attributed not to calcium polysulphide itself but to the hydrogen sulphide formed through reaction of the polysulphide components with water and carbon dioxide [2]. And for the spray to reach every point of the bark, the wood has to be bare: with foliage present, coverage is impossible.

The first resistance in history San Jose scale (Quadraspidiotus perniciosus) in Washington State was the first documented case of arthropod resistance to a pesticide, and the pesticide was lime sulphur. Melander published it in 1914 in the Journal of Economic Entomology, under a title that put the question directly, “Can insects become resistant to sprays?” [10]. At Wawawai in Washington the material worked; at Clarkston, however, 90% of the scales he had sprayed survived, and when he increased the active ingredient tenfold 74% still survived [10]. He himself wrote that the scale had “become acclimatized to a sulphur-lime environment” [10]. Lime sulphur is therefore not a material “free of resistance risk” merely because it is old and inorganic.

In Greece there is no authorisation against scale insects What precedes is history and physiology. In the current Greek Ministry approvals database, lime sulphur has eight authorised uses and no more, all against fungal diseases: scab on apple and pear, brown rot on sweet cherry, apricot, plum and peach, and powdery mildew on wine and table grapes [5]. No authorisation covers scale insects or mites. A lime sulphur spray applied for the purpose of controlling scale is therefore off-label use and is not permitted in Greece, whatever the foreign literature supports. These approvals are valid in Greece only; readers elsewhere must check their own national register.

There is, even so, a reality worth stating plainly without turning it into a recommendation. The authorised winter treatment on stone fruit against brown rot, at 1.6 to 2.4 litres per strémma (16 to 24 litres per hectare of product), is made at exactly the time and in exactly the manner that historically hit the overwintering stages of scale insects: bare wood, high spray volume, complete wetting of the bark [5]. Whatever is achieved there against scale is an incidental outcome of a lawful treatment aimed at something else. It is not a claim, it is not on the label, it is not measured, and it does not replace an authorised scalicide. Product choice for scale is made from the approvals database according to the crop and the species.

And a cost that does not show Calcium polysulphide is acutely toxic on contact not only to phytophagous mites but also to the predatory mite Galendromus occidentalis [6]. In a planting where the balance with beneficials is working, a winter application is not a neutral act; it takes out the ally along with the adversary. The same applies to products used in organic production: certification does not imply selectivity.

4. Regulatory status and the authorised uses in Greece

Lime sulphur is an approved active substance in the European Union under Regulation 1107/2009 [4], and it is permitted in organic production as a substance of traditional use [2] [4].

A historical detail that explains the confusion The EFSA assessment of 2010 did not conclude in an approval: the process was terminated when the applicant withdrew its support, following the non-inclusion decision of 2008 [1]. The substance was approved later. Anyone finding the 2010 report today and concluding that lime sulphur is not permitted is reading an out-of-date document correctly. Its toxicological and ecotoxicological values, however, remain the most complete available and are used throughout this article.

4.1 The eight authorised uses

On the Greek market there is a single product with this active substance, at 38%, classified as a fungicide. The table gives the official authorised uses with their rates. One hectare equals ten Greek stremmata; the rates below are given per hectare.

Crop	Target	Rate	Pre-harvest interval	Maximum applications
Apple	Apple scab	12 to 22.5 litres per hectare	30 days	11
Pear	Pear scab	12 to 22.5 litres per hectare	30 days	11
Sweet cherry	Brown rot	16 to 24 litres per hectare	30 days	5
Apricot	Brown rot	16 to 24 litres per hectare	30 days	5
Plum	Brown rot	16 to 24 litres per hectare	30 days	5
Peach	Brown rot	16 to 24 litres per hectare	30 days	4
Wine grape	Powdery mildew	10 to 20 litres per hectare	30 days	5
Table grape	Powdery mildew	10 to 20 litres per hectare	30 days	5

Extracted from the authorisation database of the Greek Ministry of Rural Development and Food, data version 4 September 2026 [5]. These authorisations are valid for Greece only; in every other country the national authorisations apply. Authorisations change; confirmation is made on the authorisation page before every application, and the label prevails.

What the table shows

The pre-harvest interval is 30 days on every use. That is long, and it rules lime sulphur out of the treatments close to harvest, exactly where brown rot pressure is highest.
Eleven applications are permitted on pome fruit, four to five on stone fruit. The difference is not accidental: it reflects the greater sensitivity of stone fruit.
There is no authorised use as an insecticide or acaricide in Greece, although the substance has documented activity of that kind. The classification is fungicide.

Sources: 1 2 4 5

5. Phytotoxicity, where the limits are

Phytotoxicity is not the exception, it is the rule Although lime sulphur controls scab effectively, phytotoxicity is frequently observed [2]. This is not a rare accident but an expected cost that has to be weighed before the choice is made.

5.1 What the systematic trial showed

The work of Venzon and co-workers tested concentrations of 0, 5, 10, 15 and 20 mL per litre of 30 degrees Baumé lime sulphur, on two different species [8].

Species	Result
Chili pepper	Even the highest concentration, 20 mL/L, caused no toxicity in the field [8]
Physic nut (Jatropha curcas)	Showed severe toxicity symptoms, which would make the use impossible [8]

The conclusion with practical value Two species, the same concentrations, an entirely opposite outcome. Tolerance is a characteristic of the species and the cultivar, not a property of the product. Furthermore, symptom severity was higher five days after spraying than on the first day [8], meaning assessing a trial the next morning is misleading.

The rules that follow

A trial on a limited number of trees, always, with the same product at the same rate, and a wait of five to seven days before the general application. That wait is not a formality: symptoms intensify over the first five days [8].
Never in a heatwave and never on foliage under water stress. Spraying is done in the evening or early in the morning.
Incompatible with summer oils. The combination of sulphur materials with oil is a classic cause of scorch; a safety interval between the two applications is required, in line with the label.

Sources: 2 8

6. Toxicity to the operator

Here lime sulphur departs radically from the image of a «mild organic product». The classification in the EFSA assessment is unambiguous [1]:

Category	Classification
Ingestion	Harmful if swallowed [1]
Skin	Irritating; may cause sensitisation by skin contact [1]
Eyes	Irritating [1]
Respiratory system	Irritating to the respiratory system [1]
Chemical compatibility	Contact with acids liberates toxic gas [1]

The mechanism of poisoning

The toxicity arises from direct caustic injury to the oesophagus and stomach, from the generation of hydrogen sulphide and sulphate, and from the induction of metabolic acidosis [1]. The relevant NOAEL after repeated exposure is 150 mg per kilogram of body weight per day, based on precisely these two findings: metabolic acidosis and severe burns of the gastro-intestinal mucosa [1].

Acute oral toxicity in rats is LD₅₀ 1,343 mg/kg [1], and the acceptable operator exposure level was set at 1.5 mg/kg body weight per day [1].

The protection recommended, and why it concerns only one phase The assessment considered operator exposure negligible, provided respiratory protective equipment is used, and noted that exposure is possible only during mixing and loading [1]. Respiratory protection was proposed explicitly as a risk management condition [1]. Consequently, the filter mask is needed at the moment the container is opened and the tank is filled, not while spraying.

Sources: 1

7. The effect on beneficials

Here lies the most serious finding in the whole article, and it is the one usually ignored: lime sulphur is harder on the predators than on the prey.

7.1 The mites, Beers and co-workers

The study tested calcium polysulphide on three orchard mite species: the predator Galendromus occidentalis and two phytophagous species, twospotted spider mite and European red mite [6].

The result, without qualification Calcium polysulphide was acutely toxic on contact to adult females of all three species, causing 58 to 100% mortality within 48 hours [6]. In the rate-range bioassay, the 4% by volume rate gave 100% mortality in the predator [6]. Most of the mortality occurred in the first 48 to 72 hours [6].

7.2 How long the residues last

The most useful part for planning is what the residues do on the leaf over time. Measurements on predator larvae gave:

Residue age	Larval mortality
Fresh, up to 7 days	89% [6]
14 days	50% [6]
22 days	17% [6]
Untreated check	8% [6]

That is, it takes about three weeks for larval mortality to fall back towards the level of the check. Larval mortality was nearly 100% from both fresh and aged residues [6].

A contradiction worth explaining While direct contact with the spray solution kills, exposure to residues only two hours old caused no mortality at all in the adult predator [6]. That is, the risk is the moment of spraying for the adults, and the persistence of the residue for the larvae. These are two different mechanisms and they call for different thinking about timing.

7.3 The predator more sensitive than the prey

The work of Venzon and co-workers measured the concentration at which the population stops growing, the point where the instantaneous rate of increase reaches zero [8]:

Pest mite Polyphagotarsonemus latus: growth halted at 9.4 mL/L
Beneficial mite Amblyseius herbicolus: growth halted at 7.4 mL/L

The predator, therefore, stops reproducing at a lower concentration than the pest does [8]. Predator survival did not differ from the control up to 12.5 mL/L, but at the higher concentrations of 15 to 20 mL/L it was significantly reduced [8].

And the critical point for practice The concentrations that the Brazilian study reports as usual in the field, in the crops it examined, range from 20 to 40 mL/L [8], that is, two to four times above the point at which the predator population collapses. The comparison with Greek data is not direct: the study tested a 30 degrees Baumé formulation, whereas the formulation on the Greek market is 38% [5], so the mL per litre do not correspond to the same amount of active substance. The concentration sufficient for the pest is distinctly lower than the usual field rate.

7.4 Predatory insects

In the green lacewing Chrysoperla externa, survival was significantly reduced at concentrations above 15 mL/L [8]. At 20 mL/L only 10% of the larvae reached adulthood. Even at 10 mL/L, where survival did not differ statistically from the control, only 50% reached adulthood [8], a sublethal effect invisible if only mortality is measured.

7.5 The parasitoids

Recent work in Colombia examined calcium polysulphide in citrus against the psyllid Diaphorina citri and its two principal parasitoids [9]. The insect is not established in Greece; the study is used here only for the effect on the parasitoids. Concentrations of 0.24% and 0.31% significantly reduced the survival of nymphs and eggs of the psyllid [9].

The adult parasitoids are wiped out

In Tamarixia radiata, adult survival at 0.1% was 36% at 24 hours and fell to zero by 144 hours. At 0.31% it dropped to 8% within 24 hours and to zero by 96 hours [9]. A similar picture emerged in the second parasitoid [9].

The reassuring finding: the percentage of parasitoid emergence from the mummies did not differ significantly between treatments [9]. The immature stage inside the mummy is protected. Therefore, a spray applied when the parasitoid population is mostly in mummies costs far less than one applied when the adults are flying.

7.6 Honey bees

Here the picture is distinctly better. Acute toxicity, both oral and by contact, is an LD₅₀ greater than 69 micrograms per bee, and the hazard quotient was found to be well below the trigger value [1]. The risk to bees, earthworms and other soil organisms was judged low for the use evaluated [1].

But not for the other arthropods In extended laboratory studies, effects of more than 50% were recorded on the parasitoid Aphidius rhopalosiphi and on the predatory mite Typhlodromus pyri, at an application rate of 3 kg of active substance per hectare [1]. The assessment itself noted that the risk assessment for non-target arthropods was not finalised, and further data were requested on whether recolonisation is possible within one year [1].

Sources: 1 6 8 9

8. Environment and aquatic organisms

Lime sulphur is toxic to aquatic organisms [1]. The values, expressed as total sulphur:

Organism	Test	Value
Fish, Oncorhynchus mykiss	96 hours	LC₅₀ 2.67 mg total sulphur per litre [1]
Aquatic invertebrate, Daphnia magna	48 hours	EC₅₀ 12.98 mg/L [1]
Algae	72 hours	EbC₅₀ 10.8 mg/L [1]

The buffer zone is not optional To achieve acceptable toxicity-to-exposure ratios, risk mitigation measures comparable to a 20-metre no-spray buffer zone from surface water are required [1]. It is among the widest buffer zones attached to any substance permitted in organic farming.

8.1 Soil and groundwater

The calcium added is not a pollutant: calcium cations have an important role in maintaining the physical and chemical properties of soils [1]. For sulphates, the assessment concluded that the potential for groundwater contamination above the drinking water limit of 250 mg/L is low [1].

The point that was left open Hydrogen sulphide forms under anaerobic conditions within the sediment, and for this no ecotoxicity data were submitted; the risk assessment could not be finalised [1]. The same applies to the impact of the quantity of hydrogen sulphide relative to natural background levels [1]. It is honest to say a gap exists, rather than treating as safe whatever was not measured.

8.2 The other use of the substance

Indicative of how chemically reactive the substance going into the tank actually is: calcium polysulphide is also used outside agriculture, for the removal of potentially toxic elements from the environment [3]. The documentation here reaches the level of the review abstract only, and the precipitation mechanism is not described in this article.

Sources: 1 3

9. What it is and how it is made

Lime sulphur, chemically calcium polysulphide, is not one compound but a mixture of inorganic complexes: divalent calcium cations (Ca²⁺) with anionic sulphur chains ranging in length from two to seven atoms [2]. The formula is written CaS_x, where x = 2 to 7 [2]. The molecular weight of calcium pentasulphide, the typical form, is 200.4 g/mol [2].

It is produced by reacting calcium hydroxide with elemental sulphur and water [2]. The final mixture also contains minor amounts of calcium thiosulphate, calcium sulphite, free sulphur and gypsum [2].

The specification, and what it means on the market Under the FAO specification for the liquid concentrate, the content of calcium polysulphide must be between 29 and 32% by weight, while calcium thiosulphate must not exceed 2.5% [1]. The thiosulphate has no fungicidal activity: the more of it a solution contains, the less active it is for its weight.

9.1 Physical properties

Property	Value
Appearance	Amber to deep ruby-red or orange liquid [1] [2]
Odour	Strong, of rotten eggs, from the release of hydrogen sulphide [1] [2]
Solubility	Soluble in water above pH 8; dissolves with simultaneous precipitation of elemental sulphur [1] [2]
Reaction with acids	Releases toxic hydrogen sulphide vapours [1] [2]
Reaction with oxidisers	Forms explosive mixtures if heated to dryness [2]
Flammability	Not auto-flammable and not explosive in the 29 to 30% form [1]

Why the pH of the solution decides what is in the tank At neutral to alkaline pH the long chains dominate, the ions S₆²⁻, S₅²⁻ and S₄²⁻ [1], and the active substance is soluble only above pH 8 [1]. Under acidic conditions the polysulphide ions turn into hydrogen sulphide [1], and contact with acids liberates toxic gas [1]. In the field, acidified spray water does not «activate» lime sulphur, it decomposes it and generates gas. This is the opposite of the habit formed with other products.

Sources: 1 2

10. The mode of action

The fungicidal, insecticidal and acaricidal properties rest on related mechanisms involving impaired electron transport and hydrogen sulphide formation [2].

The three strands

Sulphur penetrating the tissue. Lime sulphur prevents disease by allowing sulphur to penetrate leaf tissues and kill germinated spores [2].
Penetration of the mycelium. The polysulphide component is capable of penetrating the fungal mycelium itself in the water phase [2], and this is what separates it from plain sulphur.
Interception of electrons. Interference in the respiratory chain reduces elemental sulphur to hydrogen sulphide, which is toxic to most cellular proteins [2].

The consequence for resistance Because the action does not target a single enzyme but hits many biochemical targets at once, lime sulphur belongs to the multi-site materials. It does not select resistant strains, and for that reason it has a particular place in programmes where the single-site actives have to be protected. The same argument applies to the other multi-site products, as set out in the article on brown rot of stone fruit.

It is this penetration that makes lime sulphur an eradicant rather than merely a protectant, and it explains why, unlike plain sulphur, it also has a curative action after infection [2].

Sources: 2

11. A practical guide to application

Before mixing

A clean tank, with no residue of an acidic product. Contact with acid liberates hydrogen sulphide [1]. Rinsing is done with plenty of water, never with an acidic cleaner.
A filter mask during mixing and loading. This is the phase with meaningful exposure, and respiratory protection was proposed explicitly as a condition [1].
Mixing in the open, in a ventilated place, never in a closed shed or inside a vehicle. Even without contact with an acid, the 2% solution at pH 10 constantly releases small amounts of hydrogen sulphide [2], and the hazard becomes acute in enclosed spaces [1].
Gloves and eye protection. The product is irritating to skin and eyes and may cause sensitisation, meaning repeated unprotected exposure creates a permanent problem [1].
Never mix to dryness and never near strong oxidisers [2].

During spraying

A 20-metre buffer from surface water [1].
Evening or early morning, never in a heatwave, never on foliage under water stress.
A trial on a few trees and a wait of five to seven days before the general application. Phytotoxicity symptoms intensify within that period [8].
No mixing with oil without the safety interval stated on the label.

Timing in relation to the beneficials

Winter and dormancy: the safest moment. Populations of beneficial mites are at their lowest.
Growing season: the residues remain lethal to predator larvae for at least two weeks, returning close to the check after about three [6]. Any plan to release beneficials has to take that interval into account.
Parasitoids: the treatment costs far less when the population is at the mummy stage than when the adults are flying [9].

Sources: 1 2 6 8 9

12. The key points

Twelve conclusions

Contact with acids liberates hydrogen sulphide [1]. It is the gravest hazard and it concerns mainly cleaning and mixing in the tank. Even without acid, however, at 2% and pH 10 the solution constantly releases small amounts of hydrogen sulphide [2], so mixing is done in the open, in a ventilated place.
Soluble only above pH 8 [1]. Acidified water does not help it, it decomposes it.
It is multi-site, hitting many targets at once [2], so it does not select resistant strains.
It has curative as well as preventive action against scab [2], rare for a substance permitted in organic farming.
In Greece it has eight authorised uses, all with a 30-day pre-harvest interval [5]. It is not a tool for close to harvest.
Phytotoxicity is frequently observed [2], and tolerance differs radically between species [8].
Phytotoxicity symptoms intensify over the first five days [8]. A trial is not assessed the next morning.
58 to 100% mortality of both beneficial and phytophagous mites within 48 hours [6].
Residues kill predator larvae for three weeks: 89% at 7 days, 50% at 14, 17% at 22 [6].
The predator is more sensitive than the prey: population growth halts at 7.4 against 9.4 mL/L [8], while field rates are 20 to 40 mL/L [8].
For honey bees the risk is low, LD₅₀ above 69 µg per bee [1].
A 20-metre no-spray buffer from surface water [1]; LC₅₀ in rainbow trout 2.67 mg/L [1].

Related articles and tools

Brown rot of stone fruit, the main target of lime sulphur in stone fruit
Tomato diseases, the same logic of multi-site products in resistance management
Plant protection products authorised in Greece, searchable by crop, active substance and target, in Greek

13. Sources

What changed in the September 2026 source audit

The audit followed a question about whether what the article says on hydrogen sulphide holds. The points concerning the mechanism were confirmed verbatim, two citations were corrected, and four points were removed because they do not stand.

Penetration of the scale cover by hydrogen sulphide. No source documents it. Removed, with an explicit note in section 3.
The return to Europe around 1850 and the use in California around 1900 against San Jose scale, aphids and mites. Both rested solely on source [3], whose full text could not be accessed. Other accounts give different dates for the same history, so both were removed rather than kept on doubtful documentation.
The chemistry of the polysulphides by pH, specifically that below pH 8 the species S₅²⁻, S₄²⁻ and hydrogen sulphide dominate. Same reason. What remains in the box in section 9 now rests on [1] alone: dominance of the long chains at alkaline pH, solubility only above pH 8, and conversion to hydrogen sulphide under acidic conditions. The practical conclusion does not change.
The reducing action against heavy metals and radionuclides with precipitation as insoluble sulphides. Narrowed to what the abstract of [3] supports, that is the use for removing potentially toxic elements outside agriculture.

In place of the earlier Melander attribution, the primary 1914 publication [10] was added, which also gives more precise figures than the general description that stood before.

The numbers in the text refer to the list below.

[1] European Food Safety Authority (2010). Conclusion on the peer review of the pesticide risk assessment of the active substance lime sulfur. EFSA Journal 8(11):1890, 45 pp. The principal regulatory source: the FAO specification of 29-32%, the hazard classification, the NOAEL of 150 mg/kg/day, the LD₅₀ of 1,343 mg/kg, the acceptable operator exposure level of 1.5 mg/kg/day, hydrogen sulphide as the toxicologically relevant compound, the values for fish, Daphnia, algae and bees, the 20-metre buffer, and the data gaps for sediment and non-target arthropods.
[2] Lime Sulfur, Technical Evaluation Report, Crops. Pesticide Research Institute for the USDA National Organic Program, 3 December 2014, 15 pp. Source for the composition CaSₓ with x = 2 to 7, the molecular weight of 200.4 g/mol, the physical properties, the mode of action through impaired electron transport and hydrogen sulphide formation, the penetration of the mycelium, the curative action against scab together with the frequent phytotoxicity, and the reduction of brown rot in peaches by up to 90%. Also, after the September 2026 audit, the source for three points previously misattributed elsewhere: the intensive historical use as a winter treatment for scales, mites and certain diseases in fruit trees, the attribution of the toxicity to insects and mites to the hydrogen sulphide formed through reaction of the polysulphide components with water and carbon dioxide, and the constant release of small amounts of toxic hydrogen sulphide vapours from the dilute 2% solution at pH 10. Full text.
[3] Dahlawi, S.M. & Siddiqui, S. (2016). Calcium polysulphide, its applications and emerging risk of environmental pollution, a review article. Environmental Science and Pollution Research. Environmental Science and Pollution Research 24(1):92-102, published online 2016, January 2017 issue. Source, at the level of the abstract only, for the use of calcium polysulphide outside agriculture in the removal of potentially toxic elements from the environment. The full text could not be accessed, which is why everything previously attributed to this source for the chemistry of the polysulphides by pH and for the history of use was removed from the article during the September 2026 audit.
[4] Lime sulphur, Pesticide Properties DataBase, Agriculture & Environment Research Unit, University of Hertfordshire. Source for the current approval status of the active substance under Regulation 1107/2009.
[5] Plant Protection Products authorisation database, Greek Ministry of Rural Development and Food. Data extracted 4 September 2026. Source for the eight authorised uses in Greece, the rates, the pre-harvest intervals and the maximum number of applications.
[6] Beers, E.H., Martinez-Rocha, L., Talley, R.R. & Dunley, J.E. (2009). Lethal, sublethal, and behavioral effects of sulfur-containing products in bioassays of three species of orchard mites. Journal of Economic Entomology 102(1):324-335. Source for the 58 to 100% mortality within 48 hours, the residue decline of 89% / 50% / 17% at 7, 14 and 22 days, the absence of mortality from two-hour-old residues, the 100% at 4% by volume, and the blossom-thinning timing at 20% and 80% bloom.
[7] Smilanick, J.L. & Sorenson, D. (2001). Control of postharvest decay of citrus fruit with calcium polysulfide. Postharvest Biology and Technology 21:157-168. Source for the reduction of green mould by 80% or more with a 1 to 4 minute immersion at 40.6 to 43.3 °C in 0.75% calcium polysulphide, the figures of 93%, 88% and 81%, the reduction of sour rot by 35 to 70%, and the loss of sulphide of about 7% per 24 hours.
[8] Venzon, M., Oliveira, R.M., Perez, A.L., Rodríguez-Cruz, F.A. & Martins Filho, S. (2013). Lime sulfur toxicity to broad mite, to its host plants and to natural enemies. Pest Management Science 69(6):738-743. Source for the zero growth rate at 9.4 mL/L for the pest and 7.4 mL/L for the predator, the field rates of 20 to 40 mL/L, the effect on the lacewing, the absence of phytotoxicity in chili pepper at 20 mL/L and the severe symptoms in physic nut, and for the intensification of symptoms by day five.
[9] Restrepo-García, A.M., Largo-Diaz, C.F. & Soto-Giraldo, A. (2025). Effect of calcium polysulfide on Diaphorina citri (Hemiptera: Liviidae) and its primary parasitoids. Revista de Ciencias Agrícolas 42(3):e3274. Source for the reduced survival of nymphs and eggs at 0.24% and 0.31%, the mortality of adult parasitoids, and the finding that emergence from the mummies is unaffected.
[10] Melander, A.L. (1914). Can insects become resistant to sprays? Journal of Economic Entomology 7(2):167-173. Source for the first published description of arthropod resistance to a pesticide: 90% survival of the scales at Clarkston, 74% still surviving at a tenfold rate, and the wording “become acclimatized to a sulphur-lime environment”. The verbatim quotations and the bibliographic details were used; the full 1914 text was not read.

Disclaimer

This article is general technical information and not individual agronomic advice or an instruction to apply anything. No commercial products are named. The rates given are the official authorised values from the Greek Ministry database at the date of extraction [5] and are provided as information, not as a recommendation. Authorisations change and differ by country; the label always overrides every other source of information.

Lime sulphur is caustic and irritating. Contact with acids liberates toxic gas [1]. Respiratory protection is required during mixing and loading, together with gloves and eye protection, and all contact with acidic products or cleaners must be avoided.

Every foliar spray on trees carrying fruit carries a risk of fruit marking and leaf scorch. A prior trial on a limited number of trees is required, with the same product at the same rate, and a wait of five to seven days before the general application. Spraying is done in the evening or early in the morning, never in a heatwave and never on foliage under water stress. Every treatment is carried out at the user's own responsibility, following on-site assessment by a licensed agronomist. Pastopoulos Agronomics accepts no liability for damage or loss of production arising from the application of this information without individual technical guidance.