Sulfur is a plentiful element found in nature. Though less commonly known than nitrogen or iron, sulfur is a vital mineral necessary for balanced soil, plant growth and reproduction. Sold as a fertilizer, an herbicide and an insecticide, sulfur affects soil pH and, therefore, must be used with care.
When the youngest leaves of a plant yellow first, a sulfur deficiency may be to blame. Before amending with sulfur, however, it is important to look at management practices that affect how minerals are accessible to the plant. Watering methods, soil pH, soil temperature and soil type affect nutrient availability to plants. Lack of water, for example, will hinder a plant's ability to take up nutrients. It is important to determine whether the deficiency is due to faulty practices or an actual lack of sulfur in the soil.
One of the oldest known pesticides, sulfur effectively controls eriophyid mites, spider mites, psyllids and thrips. As an herbicide, sulfur helps fight powdery mildew, downy mildew, apple and pear scab, peach leaf curl, certain rusts, leaf blights, fruit rots, anthracnoses and cankers. Generally used with vegetables and fruits, such as beans, potatoes, tomatoes, peas, nut crops and fruit crops such as grapes, apples, pears, cherries, peaches, plums and prunes. Sulfur in large doses lowers soil pH and, when necessary, is used to quickly acidify the soil.
Sulfurs come in many forms: dust, wettable powder, paste or liquid. Lime sulfur is a liquid combination of sulfur and lime used primarily as a dormant spray. Bordeaux mixture, generally used as a fungicide, is produced by a reaction between copper sulfate and calcium hydroxide.
To prevent plant injury, sulfur should not be used in dry, 90-degree Fahrenheit or hotter weather, nor should it be combined with other pesticides. Using sulfur on plants within 20 to30 days of applying spray oils can lead to phytotoxicity. Lime sulfur is considered dangerous because of its potential to burn skin and eyes and injure plants when used in 80 degree F or higher temperatures. Bordeaux mixture may be phytotoxic to plants when applied in cool, wet weather.
Proper garden practices, soil management and consistent irrigation methods often eliminate or, in the very least, minimize the necessity for insecticides and fungicides. With generously amended soil, the need for additional sulfur as fertilizer or pH adjuster is unlikely. Tending your garden with care is not only the best recipe for pest and disease prevention, but the safest.