Gardening Wisely... A cautionary tale of oil, copper and sulfur... organic options that do NOT play well together!
Just because it says "organic," does not mean we should use the product with impunity, without regard to timing, possible plant sensitivity or potential reactions with other products. We should also be aware that while an "Omri" (Organic Materials Review Institute) listing make "safer" control options more easily identifiable, companies must pay and subscribe to be included, to display this badge on their products. There are many products that unfortunately may be overlooked, that are produced in an environmentally-sensitive manner and that are indeed kinder to the environment than older, harsher controls. The fact that they are considered safer to use and may even be labeled as being favored by organic gardeners, is sometimes lost in the growing array of safer alternatives. So, do your research, talk to fellow gardeners and knowledgeable garden center personnel, as you seek safer control options.
Let's start with horticultural oil. Considered a safe control option, it works by suffocating insects and/or their egg cases. It is quite effective on mature scale, as well as the crawler stage. Scale insects are covered with either a waxy coating or an armored shell, but since all insects breathe through their bodies, oil will simply suffocate them. Obviously, it is important that you are very accurate in your application, as any missed will continue to thrive. There is no residual action with oil, so you "get what you hit"...no more, no less. You may or may not realize that horticultural oil is a petroleum byproduct. Because it is so highly refined, it is considered safe for the control of many pests on a diverse collection of plants. You may not find an "OMRI" listing on every brand, but you will often find the "For Organic Gardening" logo, as in that displayed on Bonide's All Seasons Oil.
Horticultural oil lists variable dilution rates, based upon season of application. The heavier, dormant season dilution provides effective control of both eggs and mature, overwintering insects, when applied during the March and November dormant seasons.
Mineral oil is sometimes available as a horticultural oil for growing and dormant season use. We do not have a source for this particular product.
You may find soybean oil, packaged for growing and dormant season application. Dr. C's Insecticidal Oil is one such product.
Canola oil is another plant oil, sometimes packaged for insect control.
Neem oil (derived from the neem tree of India, the oil is expressed from its seeds) provides mildew suppression, as well as a fairly broad-spectrum control of many insects. One of the safest means of control available, with low impact on beneficials, Bonide’s Neem Oil also provides control of overwintering pests when applied as a dormant season spray.
Many gardeners turning to oils as a natural control are discovering that the essential oils of such familiar plants as peppermint, rosemary, clove and cinnamon are useful in preventing and controlling many insects and diseases. Mildew, black spot, aphids, mealy bugs, scale, and beetles are among the problems that are safely addressed. Pharm Solutions is a company that offers quite an array of natural, plant oil-based controls, with a good overlap of insecticidal and fungicidal properties. Rose Pharm, Veggie Pharm, Flower Pharm, and Fungus Pharm are among their product line that we keep in stock.
Final word… this first statement bears repeating… "Just because it says 'organic,' does not mean we should use the product with impunity, without regard to timing, possible plant sensitivity or potential reactions with other products." To avoid phytotoxicity, follow this advice…… Allow 4 weeks between applications of copper and sulfur*… 4 weeks between horticultural oil and sulfur. Horticultural oil and sulfur do not play well together, nor do plant oils like canola or soybean oil. Horticultural oil and copper do play well together [this oil is frequently combined with LiqiCop or copper soap as a dormant season or delayed-dormant season spray].
*Typical example: You apply a combination of Bonide All Seasons Oil and LiquiCop in November and again in March. Your growing season control of choice is Bonide Orchard Spray. This pyrethrin/sulfur combination (both organic compounds) is invaluable for the first four spring applications… if most of March remains too cold for your dormant season application, you may not have 4 weeks between that oil/copper application and your first pyrethrin/sulfur home orchard spray, which should occur at green tip stage… beware of potential plant damage and avoid phytotoxicity by careful scheduling of all applications!