They can be useful in controlling a wide variety of soft-bodied pests. But beware - they eliminate a broad array of pests. Care must be taken not to eliminate overwintering or slow-moving larval beneficial insects. They act as an excellent surfactant and wetting agent for fungicides such as lime sulfur and copper, also used during the dormant season. Pests have developed little or no resistance to horticultural oils, unlike numerous other pesticides on the market.
Horticultural oils are relatively inexpensive.
They are less harmful to adult beneficial insects. They are certified for organic use. Horticultural oils are by no means perfect, warned Gredler. Under the wrong conditions, horticultural oils may cause some damage or burning to certain plant foliage. To ensure against harm to your foliage, spray a small area first and wait a few days to see the effects.