Definition - What does Lime Sulfur mean?
Lime sulfur (lime sulphur in the UK) is a fungicide and insecticide used to remove, kill and/or treat grapevines that suffer from fungus, rot or mildew. It is applied to the grapevines either during the dormant season or during the growing season. Lime sulfur is safe to use on fruits, trees, vegetables and ornamental plants as well as grapevines. However, lime sulfur is corrosive; sulfur itself would cause burns through the foliage of the vine were it not buffered by the added lime, which acts to soften the effects of sulfur, diluting it so that it is beneficial rather than detrimental to the vines.
Lime sulfur is applied to the vines either as a liquid (reddish-yellow in color with a distinctive bad odor) or as a dust. It is effective against foliar fungus (and other fungi), black knot, bacteria, insects, scale, black rot, bunch rot, botrytis rot, trunk wood rot, diseases caused by phomopsis cane, leafspot (Phomopsis viticolb), powdery mildew (Erisphe necator), measles (both Togninmia and Phaeoacremonium), green berry (Cladosporium cladosporioides) and Petri disease.
WineFrog explains Lime Sulfur
Lime sulfur is composed of inorganic sulfur and lime. It is created by boiling calcium hydroxide and sulfur together with a small amount of surfactant (a substance that tends to reduce the surface tension of a liquid in which it is dissolved). The sulfur in the mix is the part that is toxic to pathogens; it kills through direct contact or fumigation by disrupting the transfer of electrons in the pathogen and transforming the sulfur into hydrogen sulfide, which is toxic to most cellular proteins. Winemakers use lime sulfur in conjunction with integrated pest management (IPM) and climate controls that encourage dry leaf and dry fruit surfaces, in order to know the best time to spray or dust the vines.
Lime sulfur is best used when sprayed in late winter or early spring when the temperature is above freezing but the leaves have not yet sprouted. The spray controls the dormant forms of disease. It can also be used during the growing season, so long as the winemaker takes care not to spray a too concentrated mixture. A more diluted mixture, with an increase of lime, is sprayed on the vines in the morning or late afternoon. Higher temperatures (over 80ºF) and dry weather increase the change of leaf injury from lime sulfur. The exact ration of lime and sulfur, and the exact application process, depend on the fungal pathogen and where the grapevine is in the growth cycle.
While lime sulfur is approved for organic production systems, it does have some negative side effects:
- Ineffective when it is windy
- Easily stray from vineyard to nearby residences or plants
- Toxic to some of the more beneficial insects and mites
- Visible in the air
- Irritating to vineyard workers (skin, eyes, respiratory system)