Submitted to: Journal of Chemical Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/15/1997
Publication Date: N/A
Citation: Interpretive Summary: Current minimum tillage and no-tillage farming systems, which have several benefits over traditional tillage methods such as providing effective control of wind and water soil erosion, nonetheless have certain drawbacks. One of the foremost of these is an increased use and dependence on chemical herbicides for weed control. Increased herbicide use has raised concerns over potential groundwater contamination and detrimental health effects from herbicide exposure. One strategy for decreasing herbicides is to grow green manures (plants grown that are turned under the soil to supply nutrients to subsequent crops) which suppress weeds. We are examining members of the crucifer, or mustard family, as potential green manures for weed suppression. In order to select crucifers which are the most suppressive to weeds, it was necessary to determine those chemicals released by the green manures which inhibited weeds to the greatest extent. Several volatile isothiocyanates, among those compounds which give mustards, cress and horseradish their distinctive odors, were identified as the most toxic to weed germination and growth. The information obtained in this study will allow scientists to select green manures which can help reduce herbicide use in minimum tillage systems.
Technical Abstract: Several members of the crucifer family including white mustard, brown mustard, black mustard, leafy turnip, rapeseed and garden were examined for their potential as allelopathic green manure crops. Hemp sesbania germination and fresh weight was inhibited by chopped leaf tissues of all green manures tested, including when added to a sandy loam soil. Wheat seed germination was inhibited by white and black mustards and cress, although none of the treatments reduced fresh weight of surviving seedlings. The major volatiles released by chopped plants were determined by solid phase microextraction sampling and identified by gas chromatography-mass spectrometry. These included allyl isothiocyanate (allyl-ITC), 3-butenyl isothiocyanate, benzyl isothiocyanate (benzyl-ITC), cis-3 hexen-1-ol, and trans-2-hexenal. These compounds, together with methyl-ITC, beta-phenylethyl-ITC, benzaldehyde, beta-ocimene, and alpha farnesene were tested for inhibition of seed germination of several crop and weed species when applied as volatiles. Of these compounds, allyl and methyl isothiocyanates were the most inhibitory, completely inhibiting the germination of all species at a headspace gas concentration of 1 ppm in airtight glass containers. Selecting mustard green manures which release high levels of allyl-ITC would appear to be optimal for allelopathic activity, although plants which produce high levels of benzyl ITC also appear promising.