A few ideas about the invention of safe biopesticides

Editor’s Note:  The materials discussed below may be applicable to organic farmers in Canada, however, it should be noted that studies still are needed to verify the effectiveness of the materials discussed.  

By André Comeau
Agriculture and Agri-Food Canada, 2560 Hochelaga, Québec, QC, G1V 2J3
May 2010

Plants contain many fungitoxic, repellent and insecticidal substances; however, using these compounds as biopesticides is not easy.  Some of these substances are volatile, others are unstable in the presence of oxygen or UV radiation, and some may be degraded by microorganisms.  In addition, an organic product must wet and adhere to the organs to be protected while negating the risk of the development of harmful organisms on these protected surfaces.

More ideas come to mind when reading Mineral Nutrition and Plant Disease (2007), a book edited by L. E. Datnoff,  W. H. Elmer and D. M Huber. Micronutrients applied to seeds as oxides have been used with some success as seed treatments against cereal diseases, and this comes from the fact that many micronutrients (and macronutrients as well) have a lot to do with natural plant resistance to diseases.

Therefore, perhaps acceptable means of improving natural plant defense systems could be found through better mineral equilibrium in plant nutrition, and through the use of extracts that contain natural defense compounds present in other plants.  When considering these strategies, we cannot ignore that protocols in organic agriculture must meet strict safety standards.
 
The use of certain micronutrients as plant defense compounds has a long track record. In France, "bouillie bordelaise", bordeaux mix, is accepted in organic culture, over time it can lead to excess copper in soils. Dr. Caetano, a Brazilian researcher, worked with EMBRAPA scientists to field-test new formulae that were much lower in copper.  The information on these tests was released for organic growers, in a Brazilian publication by Meirelles and Rupp (2005).

Dr. Caetano also performed tests with various other plant extracts. He strongly recommends flax based products.  But, he also suggests that other products that contain natural unsaturated oils could also be used.  Such product would, however, likely need to be harvested before ripening so as to have the correct properties (wetting and sticking). Thus, the timing of harvest is critical and, for most crops, too difficult. Who could, for example, harvest soybeans or sunflowers while still green, at a point when, in theory, their compounds might work?  Flax is ideal because the ripe seeds are easy to store, and known to work as spreader-sticker (possibly a result of its omega-3 oils). Avocado fruits taken at a precise ripening stage (still quite hard) were also found to be useful.
 
Fresh flax contains oxygen-reactive oils that can bind copper to the leaf surface; this is also how it works to bind other products. To maintain the binding properties, exposure to oxygen must be minimal while preparing the product. Fabricating a long-lasting product that is easy to apply necessitates experimentation. One should not grind dry flax and mix afterwards with the acidic liquid, as this gives inferior results and the copper is not bound strongly enough to the leaves.  Grinding flax in liquid can be done only with the best kinds of blenders, those that reach the very highest speed; Caetano describes the final texture as mayonnaise-like. A blender speed of 25000 rpm is the minimum, but only a few machines can go above 22000 rpm. Moreover, ground flax turns into a paste and not a powder.  If grinding could be done in liquid nitrogen, one would get a true powder, and the oxidation that spoils the result would be limited.  But, it becomes very technical if one wants to do it that way.

About five years ago, this information was sent to Guy and Yvette Durand in France. They and others tried to solve the technical difficulties, experimenting with diverse grinding machines and filters.  It took some time, but now they are beginning to get interesting results. This was done, for example, in St-Cassien by the group ADABio who found promising results on onions, grapes and potatoes ; however, on apples, the success was not as hoped.

Dr. Caetano has other valuable ideas, however, he is, like myself, more of a geneticist than a specialist in organic pesticides, and he cannot take these avenues much further as a research topic of his own. Thus, I felt it was timely to share the ideas of Dr. Caetano with others, since the early results had shown value, but the current research on those concepts was not as active as it should be.  Note that he would not recommend the use of products of animal origin, or plants that are known as toxic to humans - safety comes first.

Other new avenues of improvement of control treatments could also be investigated; for example simple sugars at doses as low as 0.1-100 ppm are elicitors of plant defence mechanisms. Fructose seems to be more powerful than sucrose.  Such elicitors were combined with conventional and organic (viral) insecticides with some success.  This being known, a number of plant extracts and honey could contain these triggering factors. A reference on this is Dr Sylvie Derridj ; she is retired from INRA but mentioned she may still answer questions in 2010.

Well-planned experimentation is the only way to find out what works.

Dr. Caetano gave his permission to translate some of his texts and share them with Canadian researchers, hoping to stimulate the imagination of others.  Translation by the Government of Canada Translation Bureau. These texts are listed below:

• Brazilian publication by Meirelles and Rupp:  The EEC Copper Mixture (originally published by Luis Carlos D. Rupp) (et en fraçais)
• EEC Sulphur Mixture with Flaxseed
• EEC Sulphur Mixture with Avocado
• An organic product with emulsifying and wetting action (Unpubluished)

Posted September 2010