Pulse recrop on clopyralid residue – implications for thistle management in Saskatchewan
Canada thistle and perennial sowthistle pose severe limitations to successful pulse crop production in western Canada. Currently, no herbicides are registered for the control of these weeds in crop; consequently they must be managed prior to sowing pulse crops. Clopyralid-based cereal products (Curtail M *, Prestige *, Prevail * and Spectrum*) offer significant control of perennial thistles in the year of treatment as well as substantive thistle reduction (average 70%) in the second year. Clopyralid soil residues can affect the growth and yield of pulse crops grown in rotation with cereal crops. Field pea recrop label restriction has recently been removed from the Curtail M, Prestige and Prevail products. Weed-free field trials were conducted in Saskatchewan between 1997 and 2001 to determine the effect on lentil, dry bean and chickpea growth and crop yield when planted the year following a clopyralid application. Clopyralid applied at 75, 100, 150 and 200 g ae/ha did not reduce stand establishment or delay crop maturity of lentils, chickpeas or dry beans sown 11 months after herbicide application. No growth inhibition or crop injury was observed in any chickpea or dry bean field trial. In 1 of 9 field sites a slight and transient effect on lentil growth was observed from clopyralid soil residue. In all field trials, lentil, chickpea and dry bean crop yield was not significantly affected by clopyralid, applied 11 months previous, at rates as high as 200 g ae/ha compared to the weed-free check. Tillage regime, zero-till and conventional tillage, prior to seeding rotational crops did not interact with clopyralid residue to affect crop injury. The data suggests that lentils, dry beans and chickpeas can be rotated the year following clopyralid application of 100 g ae/ha.
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