Dormant oil is actually horticultural oil (mineral oil) applied during the dormant period. This pesticide is used to treat trees and shrubs that are susceptible to insects and mite attack. Sulphur slurry (sulphur lime) is mainly used on trees and shrubs as a fungicide. This pesticide is used to treat trees and shrubs with diseases that can attack them.
Horticultural oil and sulphur spray can be used during dormancy (in the spring, before buds hatch) or at lower concentrations during the growing season. During the dormant period, horticultural oil can be combined with sulphur spray, in accordance with the manufacturer’s recommendations. During the growing season, there is a 30-day delay between an application of horticultural oil and a sulphur spray treatment.
During dormant periods, horticultural oil should be sprayed before bud break and when there is no risk of frost or rain within 24 hours of application. To make the treatment more effective, it is best to wait until daytime temperatures reach 12 to 15°C for 3 to 4 days. An application too early will not give satisfactory results. On the other hand, if the oil is sprayed too late (when the buds start to open), it can damage several plants and even prevent fruit production for fruit trees.
Caution: Read the product label carefully before any treatment to find out how to apply it, the precautions to take during treatment, the risks of phytotoxicity to certain plants, etc. Always keep pesticides out of the reach of children.