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Wigfield et al., 1994

Wigfield, Y. Y., Deneault, F., & Fillion, J.; “Residues of glyphosate and its principle metabolite in certain cereals, oilseeds, and pulses grown in Canada, 1990-1992;” Bulletin of Environmental Contamination and Toxicology, 1994, 53(4), 543-547; DOI: 10.1007/bf00199024.


Glyphosate, sold under the trade names of Roundup R (for ground application) and Vision R (for forestry use), is a non-selective herbicide which is absorbed through the leaves and translocated throughout the whole plant. The herbicide, when applied close to harvest for late season weed control and possible harvest management benefits, can result in the presence of residues throughout the whole plant including the seed coat. In Canada, glyphosate is registered for pre-plant and post-harvest uses and until June 1991, it was not registered for direct application on crops. Diquat, a fast acting herbicide, is registered for desiccation of canola, mustard, field peas, flax, soybeans, and lentils. While diquat is effective as desiccant, it is not particularly effective in controlling perennial weeds and it is not registered for use on cereals. In June 1991, a temporary registration was granted for pre-harvest application on flax for control of quackgrass, seasonlong control of Canada thistle and perennial sow thistle and harvest management by drying down the crops. In June 1992, the same registration was granted for application on certain cereals (wheat and barley), oilseeds (canola/rapeseeds and soybeans) and pulses (peas and lentils), and in June, 1993 it was granted for malting barley. The pre-harvest use may also provide soil conservation benefits by reducing the use of cultivation as a means of weed control. The maximum residue limit (MRL) (Doliner and Stewart, 199 la) when crops are treated with the proposed label directions (single application at the rate of 0.89 kg/ha glyphosate and the time of 7-14 days before harvest) are shown in Table 1. Registration for use on beans has not been granted due to insufficient residue data.

However, because glyphosate is effective as herbicide and provides harvest management benefits, in 1990 questions were raised from Agriculture Canada field inspection staff regarding the potential misuse of the herbicide which at that time was not registered for pre-harvest use on crops. Thus a post-harvest survey was conducted to monitor glyphosate residues in these cereals, oilseeds and pulses grown during 1990-1992 period to check if the registration uses of glyphosate were being followed. This paper presents the 3-year monitoring results comprising 459 samples of 8 different crops grown in 7 different provinces in Canada. FULL TEXT

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