It is fairly easy to accidentally damage your plants or nearby environments when applying horticultural oils. Here are some important points to consider before using these oils:
Only spray plants with confirmed pest problems in order to conserve the beneficial insects in your garden and landscape.
Be aware that junipers and spruce often lose their blue color when oil is applied.
Oil and water do not mix: horticultural oil will inhibit oxygen transfer, which can kill fish. Keep applications and their airborne oil drift out of waterways.
For information on how to use horticultural oils successfully, see the WSU Extension fact sheet Pesticide Ingredient: Horticultural Oil.
Submitted by: Catherine Daniels, Jan. 7 2016