http://www.ortho.com/index.cfm/even...l/documentId/a69ec3d28e01117707546b170426b519
Active ingredients: 97% petroleum oil
Where to Use: For outdoor use only. On conifers, roses, shrubs and trees, including apples, apricots, cherries, peaches, pears, plums and citrus (grapefruits, lemons, limes, oranges and tangerines)
Where Not to Use: Maidenhair ferns, red maples, Japanese maples or
non-woody plants unless otherwise specified. Volck® Oil Spray may cause discoloration to blue spruce.
Cautions: Only use this product outdoors.
http://www.yardener.com/UsingHorticulturalOil.html
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.