The basic situation of chlorothalonil

Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) is a polychlorinated aromatic mainly used as a broad spectrum, non-systemic fungicide, with other uses as a wood protectant, pesticide, acaricide, and to control mold, mildew, bacteria, algae. Chlorothalonil-containing products are sold under the names Bravo, Echo, and Daconil. It was first registered for use in the US in 1966. In 1997, the most recent year for which data is available, it was the third most used fungicide in the US, behind only sulfur and copper, with some 12 million lbs used in agricultural alone that year. Including non-agricultural uses, the EPA estimates that on average almost 15 million lbs were used in annually from 1990-1996.
Chlorothalonil is commercially available in many different formulations and delivery methods. It is applied as a dust, dry or water-soluble grains, a wettable powder, a liquid spray, a fog, and a dip. It may be applied by hand, by ground sprayer, or by aircraft.