In horticulture, lime sulfur (lime sulphur in British English, see American and British English spelling differences) is mainly a mixture of calcium polysulfides and thiosulfate[1] (plus other reaction by-products as sulfite and sulfate) formed by reacting calcium hydroxide with elemental sulfur, used in pest control.
After elimination of residual solids (flocculation, decantation, and filtration), it is normally used as an aqueous solution, which is reddish-yellow in colour and has a distinctive offensive odor of hydrogen sulfide (H2S, rotten eggs).
The exact chemical reaction leading to the synthesis of lime sulfur is generally written as: as reported in a document of the US Department of Agriculture (USDA).
Lime sulfur is approved for use on organic crops in the European Union and the United Kingdom.
Without paint pigments, the lime sulfur solution bleaches wood to a bone-white color that takes time to weather and become natural-looking.
[6] In the very specific case of the bonsai culture, if the lime sulfur is carefully and very patiently applied by hand with a small brush and does not enter into direct contact with the leaves or needles, this technique can be used on evergreen bonsai trees as well as other types of green trees.
Diluted solutions of lime sulfur (between 1:16 and 1:32) are also used as a dip for pets to help control ringworm (a fungus), mange and other dermatoses and parasites.
Lime sulfur solutions are strongly alkaline (typical commercial concentrates have a pH over 11.5 because of the presence of dissolved sulfides and hydroxide anions), and are harmful for living organisms and can cause blindness if splashed in the eyes.
However by the 1940s, lime sulfur began to be replaced by synthetic organic fungicides which risked less damage to the crop's foliage.