Sulfur is one of the most ancient fungicides used for the plant health defense. Generally the sulfur is used to fight the Oidium of the grapes, of the fruit plants, of the vegetable crops, of the cereals and sugar beet. The sulfur results effective for other diseases too such as grape excoriose, septoria, fusarium and rust of wheat. Sulfur is explicating also a collateral insecticidal action against the neanic stages of aphids, thrips and acaricidal against the pear leaf and grape leaf blister mites.
The action of sulfur against Oidium is preventive given that it avoids the germination of conidium, curative because acts on the mycelium during the incubation and eradicator because eliminates fungus when visible. The fungicide activity of the sulfur is due to its capability to penetrate in the fungal cell, given its fat-solubility, breaking the cell membrane. This causes the leakage of the water from the fungus and its consequent death for dehydration.
The fungicide activity of sulfur depends from the temperature, from the related environmental humidity and the fineness of the particles. Sulfur explicates its action passing from solid to the vapor state and consequently low temperatures and high humidity reduce its effectiveness. The thinnest sulfurs start to become active around 10-12 °C while the roughest ones become active at temperature at least 18-20 °C. Beyond 28 °C sulfur becomes phytotoxic.
The sulfur products for plant health are available in the market in various formulations. The sulfurs for powdery treatments are divided in sublimated sulfurs, obtained from the distillation of the raw mineral and constituted by particles included between 5 and 14 microns; ventilated sulfur obtained by the grinding of the raw mineral and constituted by particles between 15 and 150 microns. Wettable sulfurs are divided in common wettable sulfurs obtained from the ventilated sulfur with the addition of wetting agents; micronized sulfurs obtained through grinding of sublimated or ventilated sulfurs and colloidal sulfurs, obtained trough chemical processes with sulfur at the colloidal state, finer than the micronized one. The effectiveness of sulfur requires a tight contact among the cells of the parasite and the fungicide product.