The tolerance of four varieties of fenugreek (Trigonella foenum-graecum L.) to seven pre-emergence and six post-emergence herbicides was tested in the glasshouse and some were studied further in the field. Because fenugreek is slow to establish, pre-emergence herbicides will usually be necessary, supplemented perhaps by a post-emergence treatment. Of the pre-emergence compounds tested, fenugreek tolerated trifluralin; methazole; chlorthal-dimethyl plus methazole; metamitron; and nitrofen at realistic rates of application. Trifluralin was particularly promising. The tolerance of fenugreek to this and other dinitroaniline herbicides was studied both in the glasshouse and in the field. A simple technique was used to investigate the site of uptake of these herbicides. Entry through the root produced a greater response than shoot entry. Laboratory arid glasshouse studies of the effect of soil properties on the phytotoxicity of these compounds showed there was a negative correlation between activity and soil organic matter content. The selectivity values of the dinitroanilines between fenugreek and weeds were compared. Trifluralin and isopropalin showed good selectivity except with cruciferous weeds which were very resistant. EPTC is very effective against a wide spectrum of weed species including many which are unaffected by the dinitroanilines, but it is marginally tolerated by fenugreek. In an attempt to improve its selectivity, the effect of herbicide safeners was examined. R25788 and MON4606 as seed treatments gave good results in pot experiments. They protected fenugreek from up to 5 kg/ha EPTC. However, high rates of safeners adversely affected fenugreek growth. Eradicane (EPTC + R25788) as a seed dressing was effective against certain weeds, but it injured the crop. In pot and field experiments, nodulation of fenugreek was affected only when plant growth was reduced by the herbicides. Abnormally low protein content was associated with high diosgenin yield. In pot experiments EPTC with R25788 or with MON4606 reduced diosgenin yield but not protein content. Diquat was used as a desiccant to enhance maturity and reduce post-harvest fungal attack. Seed from desiccated plants yielded more diosgenin than from non-desiccated plants. Pre-planting soil incorporated trifluralin or isopropalin is recommended for weed control in fenugreek. Either MCPB or bentazone plus MCPB is recommended as a supplementary post-emergence treatment for resistant weeds.
|Date of Award||1983|