Many people like to purchase organic produce because they believe that it has not been sprayed with pesticides. This is not a correct assumption. The fact is most organic fruits and vegetables have been sprayed, but with different products.
Without treatment, many crops such as apples, tomatoes, cabbage and cherries would be of such poor quality due to insect and disease damage that most people would refuse to eat them. Although pest occurrence and level of damage can vary in different areas of the country, just about all farmers must apply some pesticides in order to maximize yield and crop quality.
The purpose of this article is not to pass judgment on how growers and gardeners decide to protect their investment, but to provide you – the consumer – with some information about the types of products that are used on organic produce.
Organic growers have a number of options when trying to manage insects and diseases. They may use pesticides that are derived from plants. These include neem, pyrethrum, rotenone and Sabadilla. They can be a contact or stomach poison or will disrupt certain metabolic processes. There are other insecticides that are living organisms such as Bacilli bacteria. These are called biopesticides. There are now more that 200 in existence formulated into more than 800 products.
The Bacillus genus of bacteria is just one example. They occur naturally in the soil. Various species are used to control moth larvae including cabbage worms, tomato hornworm and various fruit worms. Other preparations are effective against potato beetles, mosquitoes and certain disease pathogens.
Diatamaceous earth, which is silicon dioxide from deposits of fossilized diatoms, is used to kill certain ground-dwelling insects while Spinosad, a metabolite resulting from fermentation of the bacteria Saccharopolyspora spinosa, works well against a wide variety of insects. Insecticidal soaps which are potassium fatty acids are used against soft-bodied insects such as aphids, immature scale and spider mites (which aren’t really insects.)
When weather conditions are right, disease-causing pathogens can cause great crop loss if not protected by chemicals called fungicides. Organic growers have fewer options in this area, but they are not totally at the mercy of Mother Nature. Sulfur has been used since the Greek empire. Bordeaux mixture (a combination of hydrated lime and copper sulfate) has been used for over a hundred years. Other copper preparations, potassium bicarbonate, neem and horticultural oils and a bacilli bacteria all have some disease prevention abilities.
In order for any of these products to be used for organic production, they must be certified by the Organic Materials Review Institute (OMRI). OMRI is a private organization that provides organic certifiers, growers, manufacturers and suppliers an independent review of products intended for use in certified organic production, handling, and processing.
If you would like additional information on using organic pesticides, watch my “Using organic pesticides in the garden” video.
--by Gary L. Heilig, Michigan State University Extension