Spraying Lime Sulfur on Grapevines

Lime sulfur is a standard fungicide that is effective against various diseases of perennial fruit crops. Developed more than 150 years ago and made from basic natural materials, lime sulfur is considered relatively safe; some formulations are even approved for organic production by the Organic Materials Review Institute. Gardeners commonly apply lime sulfur to grapevines and other small fruit crops.

A French gardener concocted the original lime sulfur in 1851. He combined sulfur, hydrated lime and water, then boiled the mixture and collected the resulting liquid. First used to control mildews, gardeners soon found lime sulfur to be effective for other botanical disorders caused by fungi. The active agent is sulfur, which has been used as fungicide for 2,000 years and is now incorporated into a variety of commercial formulations. In some situations, sulfur is toxic to plants as well as fungi; the addition of lime reduces the toxicity of sulfur so that the resulting mixture is safer for plants yet still effective against fungal pathogens.

Gardeners usually employ lime sulfur as a dormant spray, meaning they apply it before new growth appears in the spring. The ideal time to apply is actually at the end of the dormant period -- that is, when leaf buds begin to swell but before any visible leaf tissue emerges. Lime sulfur is caustic and will burn sensitive leaf tips. Weather is variable at this time of year, so apply when temperatures are above freezing. An appropriate application rate for dormant spraying is 10 pounds of lime sulfur mixed into 100 gallons of water.

You can apply lime sulfur during the the growing season if this is your only chance to control a troublesome disease condition, but be especially careful to avoid injuring succulent leaf and vine tissue. Nondormant spraying requires a less-concentrated solution -- about 5 pounds of lime sulfate per 100 gallons of water. Weather conditions influence the degree of injury. Lime sulfur is more likely to burn your grape vines when the weather is dry and ambient temperatures are above 80 degrees Fahrenheit. If you cannot wait for a cool day, apply in the early morning or late afternoon.

Lime sulfur is a generic fungicide, so it is a good choice whenever you observe symptoms of a disease caused primarily by fungi. Dormant spraying of lime sulfur is an important technique for controlling a serious fungal disorder known as anthracnose of grape. You can use it also used for grape vines suffering from phomopsis, black rot or powdery mildew. Lime sulfur is not commonly employed as an insecticide, but it may be helpful if your grapes are afflicted by insects that overwinter on dormant vines.