Garden & Greenhouse October 2017 Issue - Page 51

the spray, so it is desirable to rinse off soap sprays 12-24 hours after application. This can be done by following sprays with a good water rinse or foliar feeding. Water Quality is very important to the effective- ness of soap sprays. Hard water reduces the effec- tiveness of soap sprays and may even render them useless. Using the purest water available is best, so it is recommended to use distilled water with soap sprays. It is best to spray a fine mist over plants rather than drenching them. Spray bottles that can produce a fine mist are available at dollar stores, but commercial sprayers that have wands make it easer to spray the underside of leaves, which is important to achieve complete coverage. The same sprayer may be used for soap and/or oil sprays as well as foliar feeds, but a separate sprayer must be used for her- bicidal sprays. As with anything that is sprayed on plants, soap sprays are best applied when it is cool, either in the morning or evening. Oil Sprays Oil sprays have been used for centuries, either alone or in combination with soap or other ingredi- ents to combat many of the same pests controlled by insecticidal soaps. Oil provides an added benefit because it has a different impact than soap on pest’s ability to survive. It has the added benefit of help- ing sprays to stick to leaves, and may provide some control of funguses such as powdery mildew, as well. Oils pose few risks to people or to most desirable species, including beneficial natural enemies of insect pests. This allows oils to integrate well with biologi- cal controls. Many gardeners use common cooking oils in their sprays, but the type of oil used can greatly im- pact the effectiveness of the spray. Cottonseed oil is generally considered the most insecticidal of the vegetable oils. Soybean oil runs a close second. The advantage of purchasing horticultural oils specifically designed for use on plants is that horticultural oils are normally combined with an emulsifying agent that allows the oil to mix well with water. Regard- less of the oil used, the mixture usually consists of a 2 percent dilution, which is similar to that used for insecticidal soaps. One to two teaspoons liquid soap added to 1 quart of water is a good general guideline. Another oil that deserves consideration for oil sprays, and has received considerable attention as an effective insecticide with some additional fungicidal properties, consists of extracts from seeds of the neem tree (Azadirachta indica). Now that we have a good understanding of op- tions and uses of soaps and oils as natural insecti- cidal controls, and hopefully an appreciation for the added benefit of combining the two, we can consider some additional natural insecticide and fungicide tools. October 2017 51