Growers Warned About Herbicide Carryover

REGINA - Mar 19/03 - SNS -- Last year's drought could continue to impact crops in parts of the province this year because of the heightened risk herbicides and other chemicals were carried over in fields.

Certain herbicides applied in 2002, for example, may not have received rain soon enough to complete their breakdown before seeding begins in 2003. Herbicide residue, therefore, may limit cropping options this year.

"The herbicide breakdown process has three major requirements: moisture, warm soil temperatures, and enough time under optimal temperatures and moisture to thoroughly degrade the herbicide and thus allow sensitive crops to grow safely. This complex process is also affected by factors such as soil pH. So in some areas of the province, the rains that arrived in the second week of August may have been too late, since temperatures also dropped off dramatically," says Clark Brenzil, weed control specialist with Saskatchewan Agriculture, Food and Rural Revitalization (SAFRR).

Referring to the "Cumulative Rainfall" map of SAFRR's August 6, 2002 Crop Report, Brenzil says areas south of the Qu'Appelle River and the South Saskatchewan River basin showed adequate moisture to that point in the growing season. June and July are the prime herbicide breakdown periods, so he is confident these areas will have no problem with herbicide carryover.

"But producers in these areas will still need to add a year to the re-cropping recommendations of any long residual herbicides applied in or before the dry year of 2001," Brenzil cautions.

"Areas to the north and west of Saskatoon are at high risk of herbicide carryover, which will restrict crop choices in 2003. Since this area has had back-to-back dry years, producers may need to consider herbicides applied in both 2001 and 2002.

"There is also a 'marginal' band lying between the two extremes - between no problems and restricted crop choices due to herbicide carryover - including the west-central, north-east and east-central areas of the province that were very dry until the second week in August when it turned very cold. In these areas, there may not have been enough time for herbicides to break down sufficiently to rely on normal re-crop recommendations. Producers may want to be conservative in their crop choices and select only those crops that are very tolerant.

"If, due to dry conditions, you had no yield last year - or for the past two years - you are at high risk of herbicide carryover," says Brenzil.

He says, furthermore, SAFRR's Nov. 1, 2002 Subsoil Moisture Map may indicate good soil moisture over much of the province but, in terms of herbicide carryover, this can be deceiving, since most herbicide residue will be contained in the top two or three inches of soil.

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