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by Ken Laing R.R. S. St. Thomas NSP 3S9
Recently, farmers and researchers have been taking a closer look at crucifers, and their effects on nematodes and some fungal diseases. (Nematodes are a serious concern for many crops, notably strawberries, raspberries, and fruit trees. ed. note) The crucifers, mustard, canola, oil radish, broccoli, etc. contain glucosinolates which give them their pungent odour, and taste. When crucifers are worked into the soil these compounds are converted to a form of isothiocyanate which is very toxic to nematodes. Its action is similar to the active ingredient in a commercial soil fumigant.
Because of its numerous advantages, we were already growing oil radish as a green manure and weed smothering crop prior to strawberries. Requiring only six weeks from seeding to plowdown means it fits neatly between crops or can used for two successive crops in one year. For nematode control, our experience has proven that it is critical to bury the growing plants since the active ingredient is very volatile and quickly lost otherwise, (i.e. mowing, wilting, then incorporating). With two successive crops of oil radish, both incorporated immediately, we have achieved good nematode control and very good growth of strawberries the following year.
Some crucifies have much higher levels of glucosinolates, and therefore isothiocyanate, than oil radish does - as much as ten times higher. However, the side effects of isothiocyanate on beneficial soil life has not yet been studied. Given our experience with oil radish, where earthworms are still present, but not plentiful, the higher concentrations of chemicals in these other plants may well prove detrimental to beneficial organisms.
Copyright © 1993 Ecological Farmers Association of Ontario. Reprinted with permission. All rights reserved.
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