Is it Safe to Mix DiPel With Sulfur to Spray Tomatoes?

Tomato Woes

• Early blight, anthracnose, virus wilts and mosaics are but a few of the diseases that afflict the tomato. Blights, viruses and many insect pests are unaffected by the kurstaki subspecies of Bacillus thuringiensis, which is the active ingredient in DiPel. Many problems, such as blossom end rot and catfacing, have environmental causes and require cultural solutions. Of the molds that afflict tomatoes, only powdery mildew responds to sulfur dust – so the use of both DiPel and sulfur is limited in tomatoes.

Dipel, the Organic Alternative

• DiPel is a branded microbial pesticide that contains a species of Bacillus thuringiensis. The Organic Materials Review Institute lists several Bt compounds on its list of approved products for organic gardening. Bt-kurstaki is fatal only to the larval forms of moths and butterflies -- caterpillars -- which include tomato pests such as hornworms and fruit worms, also known as corn earworms. The pesticide is effective when caterpillars are young in the spring. At other times, predators such as parasitic wasps might be more effective. DiPel is sold as a vegetable and fruit dust or as a concentrate that may be mixed in a solution of 1 to 2 teaspoons per gallon of water for home crops.

Sulfur, a Versatile Garden Aid

• Sulfur has several uses in the home garden, including soil improvement. Sulfur dust kills mites, but mites are not common on tomatoes. Sulfur offers good control of powdery mildew when used on very young plants. Powdery mildew occurs primarily in late summer or fall when nighttime temperatures begin to fall -- and when mature plants can typically withstand the mold. Sulfur should not be used when temperatures rise above 90 degrees Fahrenheit or within two weeks of use of an oil spray, such as neem oil. Clemson University recommends 20 to 30 days between use of sulfur and horticultural oils. Sulfur is sold in powder form for the home gardener and as wettable powder, but it must be carefully mixed and applied uniformly to avoid burns.

Timing and Compatibility Concerns

• Although some combinations of DiPel and sulfur are marketed for agricultural use, the Environmental Protection Agency canceled registration for older combinations of Bt and sulfur. Clemson University recommends against mixing sulfur with other pesticides. HORTUS, an Australian consultancy, says Bt is incompatible with lime sulfur but can be paired with wettable sulfur. Considering the differences in timing and application for Bt and DiPel to tomatoes, home gardeners should use products specifically labeled for use on tomatoes separately rather than mixed.