Study of persistance and accumulation over time of residual herbicides used prior to sowing of sugar beet in crop rotation
2000
Cioni, F. | Tugnoli, V. (Associazione Nazionale Bieticoltori, Bologna (Italy)) | Rapparini, G. | Marchi, F.
It is a widespread practice where sugarbeet is rotated with other crops to use residual action type herbicides belonging to the sulphonylurea and imidazolinone families of chemicals. These are typified by a high biological activity when applied at a rate of a few grams per hectare, performing their destructive action through the same mechanism, namely inhibiting the action of the enzyme ALS (Acetolactate synthase). The repeated use of these herbicides has been connected on occasion with the appearance of phytotoxic symptoms in beet crops during the early stages of development. From the experimental results of four crop rotation programs in which beet was preceded by maize, soya and wheat, it was show by biological tests that in the medium texture and clay soils of Emilia-Romagna, chlorsulfuron was present in spring following the wheat crop at a rate of less than 0.06 ppb, imazamethabenz-methyl at a rate of less than 9.8 ppb, triasulfuron at a rate of less than 0.06 ppb, amidosulfuron at a rate of less than 0.2 ppb, and tribenuron-methyl at between 0.09 and 0.18 ppb. These concentrations did not cause any manifest symptoms of phytotoxicity in the crop, though imazamethabenz, amidosulfuron, triasulfuron and chlorsulfuron did in certain instances have a negative influence on productivity parameters. There was also serious damage caused by chlorsulfuron, amidosulfuron, imazamethabenz-methyl and triasulfuron, both of a visible nature and in terms of productivity, particularly in the sub-acid soils of the province of Foggia. Three year tests confirmed the absence of directly induced phytotoxic phenomena, albeit without determining the effects deriving from accumulation. At all events, these tests have made it possible to establish phytotoxicity risk thresholds in respect of the active constituents employed.
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