What Are Horticultural Sprays?
Volk Oil also called Dormant Oil
One of the most effective and least toxic insecticides on the market are horticultural oil. There are two grades of horticultural oil. Volk Oil is the traditional heavier grade oil, which is used as a preventive spray on fruit trees in early spring,
Traditional heavy horticultural spray oils have a viscosity of 100 to 200. If used indiscriminately on plant foliage, they can clog the pores on leaves and buds, cutting off respiration and killing the plant. These dormant oil sprays were designed to be used in fall through early spring on plants that have lost their leaves during the winter, primarily fruit trees. Applied to branches and stems while trees are leafless, the oil smothers insect eggs hidden in the bark.
Light Horticultural Oil
Light horticultural oils are very effective insect controls because they can be used on foliage without harming trees even in the summer months. This newer type of oil, often called "superior" horticultural spray oil, is lighter and less viscous (60 to 70) than heavy oil and evaporates much more quickly from leaves and stems. Any common woody ornamental plant can tolerate a spray using a 2-percent solution of this oil, as long as the plant is healthy, soil moisture adequate, and the relative humidity creates conditions for fairly rapid evaporation of the oil.