Lime sulfur

In horticulture, lime sulfur (British spelling lime sulphur) is a mixture of calcium polysulfides formed by reacting calcium hydroxide with sulfur, used in pest control. It can be prepared by boiling calcium hydroxide and sulfur together with a small amount of surfactant. It is normally used as an aqueous solution, which is reddish-yellow in colour and has a distinctive offensive odour.

A New York State Agricultural Experiment Station recipe for the concentrate is 80 lb. of sulfur, 36 lb. of quicklime, and 50 gal. of water. About 2.2:1 is the ratio (by weight) for compounding sulfur and quicklime; this makes the highest proportion of calcium pentasulfide. If calcium hydroxide (builders or hydrated lime) is used, an increase by 1/3 or more (to 115 g/L or more) might be used with the 192 g/L of sulfur. If the quicklime is 85%, 90%, or 95% pure, use 101 g/L, 96 g/L, or 91 g/L; if impure hydrated lime is used, similarly increase its quantity. Avoid using lime that is less than 90% pure. Boil for an hour, stirring and adding small amounts of hot water to compensate for evaporation.

Lime sulfur is sold as a spray for deciduous trees to control fungi, bacteria and insects living or dormant on the surface of the bark. Lime sulfur burns leaves so it is not as useful for evergreen plants.

Bonsai enthusiasts use undiluted lime sulfur to bleach, sterilise, and preserve deadwood on bonsai trees while giving an aged look. Rather than spraying the entire tree, as with the pesticidal usage, lime sulfur is painted directly onto the exposed deadwood, and is often colored with a small amount of dark paint to make it look more natural. Without paint pigments, the lime-sulfur solution bleaches wood to a bone-white color that takes time to weather and become natural-looking. Because the lime sulfur does not contact the leaves or needles, this technique can be used on evergreen trees as well as other types of trees.

Diluted solutions of lime sulfur (between 1:16 and 1:32) are also used as a dip for pets to help control ringworm (fungus), mange and other dermatoses and parasites. Undiluted lime sulfur is corrosive to skin and eyes and can cause serious injury like blindness.

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