Lime sulfur sprays can improve spring disease control
Early sprays of lime sulfur reduce disease inoculum in spring
Many diseases of woody perennial plants overwinter as lesions on the plant or areas that were killed the previous year. Spores from last year’s infection reinfest new growth in the spring. Caustic sprays in the early spring can burn the lesions, killing or damaging the fungal spores before they are released in the spring.
Lime sulfur is an effective dormant spray when applied early in the season as growth begins. When applied as a true dormant spray before growth begins, lime sulfur can be used with oil to increase the penetration of the caustic sulfur into the surface of the infected tissues. Once green tissue appears, oil should not be mixed with oil. Oil will carry sulfur into green plant tissue causing injury. It is generally recommended to not use oil within a week of a sulfur spray when green tissue is exposed. Lime sulfur rates should be reduced when green tissue is exposed. Recommended rates vary for different products with dormant rates in the 10 to 12 pounds per 100 gals of water to 5 or 6 pounds when green tissue is exposed.
Lime sulfur (calcium polysulfide) is a caustic material and after application it breaks down, releasing sulfur. It is very effective against diseases that overwinter on the host. Lime sulfur is also effective against many insect pests that overwinter on the plant.
Lime sulfur is registered for use on most fruits, but is most commonly used on small fruit. Lime sulfur is used on brambles to control anthracnose, spur blight and cane blight. In blueberries, the diseases controlled include phomopsis and anthracnose twig blights. In grapes, lime sulfur is effective against black rot, powdery mildew and phomopsis. Lime sulfur is also used in apples, pears, peaches and cherries.
Some formulations of lime sulfur are OMRI certified as organic, but check with your certifier for confirmation.
Sulforix is a commercial formulation of lime sulfur. It can also be used as a dormant spray to burn overwintering fungal lesions. Sulforix is also registered for application during the growing season in some crops, especially in the prebloom period.