Appropriate crop seeding rate when herbicide rate is reduced

A study was conducted at three locations in Saskatchewan, Canada, in 1996 a nd 1997 to determine if increasing the seeding rate of wheat, barley, and l entil by 50% would maintain weed control and crop yield when herbicides are applied at reduced rates or not at all. Three herbicide rates (1/2 of full , 3/4 of full, and full recommended label rate), along with an untreated ch eck, two crop seeding rates (normally recommended and 1.5 times normally re commended rates), and three crops were tested. Increasing seeding rate did not affect weed fresh weights, crop yield, and net return responses to herb icides applied at reduced rates or not at all when averaged across crops, y ears, and locations. Increased seeding rate, independent of the different h erbicide applications, had infrequent and inconsistent effects among the cr op by year by location combinations. More broadleaf and grass weed growth, less crop yield, and lower net returns generally occurred when herbicides w ere not applied or applied at reduced rates. These trends were especially p rominent when herbicides were not applied to cereal crops at Saskatoon (40% yield reduction) and when herbicides were applied at 1/2 the full label ra te rather than higher herbicide rates to wheat at the other two locations ( 16% yield reduction). In 1996, lentil yield and net returns did not respond to herbicide application and rate because of poor grass weed control acros s all herbicide rates. Lentil yield and net returns decreased by 11% (full vs. 3/4), 22% (3/4 vs. 1/2), and 46% (1/2 vs, none) when herbicides were ap plied at progressively lower rates in 1997. Reduced herbicide rates did not affect net returns for cereal crops, indicating that herbicide rates lower than the full label rate may be economically viable in certain crops.