Growing grapes can be a fun and exciting pastime for you and your children that provide fresh, juicy fruit for your little ones to snack on. Grapes (Vitis spp.), which grow throughout U.S. Department of Agriculture plant hardiness zones 5 through 9, are susceptible to a number of fungal disease that may require spraying the grapevines with lime sulfur to control. Before the treatment, however, familiarize yourself with lime-sulfur spray and its warnings to reduce risk of harm to your family and your grapevines.
1. What is Lime-Sulfur Spray?
Lime sulfur is a fungicide and insecticide used to control a wide array of diseases and pests, including powdery mildew, scale, black rot and phomopsis. It is safe for use on most fruits, trees, vegetables and ornamental plants. In 1851, the head gardener at the vegetable houses in Versailles, France developed lime sulfur while he was searching for a fungicide to protect his plants from mildews. It is the sulfur in the mixture that is toxic to fungal pathogens, killing them through fumigation or direct contact. However, sulfur is also toxic to some plants causing a phytotoxic reaction. By adding lime to the mix, the possibility of a phytotoxic reaction is reduced and makes the solution safer for plants.
2. Grapes and Lime Sulfur
Certain species of grapes are sensitive to sulfur. Sulfur sensitive grapes include “Concord” (Vitis labrusca “Concord”), "DeChaunac" (Vitis “DeChaunac”), “Chambourcin” (Vitis “Chambourcin”), “Ives” (Vitis labrusca "Ives"), “Chancellor” (Vitis “Chancellor”), "Marechal Foch" (Vitis “Marechal Foch”), “Rougeon” (Vitis “Rougeon”) and “Foch” (Vitis “Foch). Gardeners should seek out an alternative to lime sulfur for fungal disease control on these grapes species. Grapes of all types can experience injury if lime-sulfur spray is applied improperly. Signs of sulfur damage include chlorosis of the leaves, which is a yellowing edges or spots on the affected leaves, leaf distortion and reduction in fruit size. The best way to prevent sulfur injury is to follow the instructions on the lime-sulfur package and avoid applying the fungicide to sulfur sensitive or unhealthy plants.
3. When to Apply Lime Sulfur
Lime sulfur can be applied in dormant or growing season. However, high concentrations of lime sulfur should only be used when grapes are dormant, because the sulfur spray may cause damage if applied when the green foliage appears, according to the Ohio State University website. A more diluted lime sulfur can be applied in the growing season if sprayed in the morning to prevent leaf injury. Furthermore, avoid applying lime sulfur during periods of dry weather or when the temperature is 80 degrees Fahrenheit or above. The exact application time and rate varies depending on the fungal pathogen you are trying to control and whether the grapevine is dormant or growing. For example, one brand of liquid lime sulfur suggests spraying the grapes in the summer when shoots are between 6 and 8 inches long, and applying a second treatment after bloom to help control anthracnose and powdery mildew.
4. Warnings and Considerations
To prevent injury, keep children and pets, as well as pregnant and nursing women away from the area while handling and applying lime sulfur. Lime sulfur can cause skin and eye irritation, and in some instances, lead to severe corneal injury and corrosion of the skin. Ingesting lime sulfur leads to corrosion and irritation of the gastrointestinal tract and results in vomiting and diarrhea. If lime sulfur encounters stomach acid, toxic hydrogen sulfide can evolve. For contact with skin or eyes, flush the area thoroughly for 15 minutes with water. If ingested, immediately contact poison control.