The questions then arise: Pre-emerge? Post-emerge? Both? Kevin Carlson, Federated's senior agronomist, said that even when a post-emerge treatment seems to be working, "there's value in the pre."
Yes, it costs more to apply both a pre-emerge and a post-emerge herbicide (and there's no argument about post). But, Carlson said, "The value [of pre-emerge herbicides] is found when comparing the best pre programs that work really well with the post alone programs . . . especially when dealing with weed resistance."
In herbicide trials conducted by the University of Minnesota last season (click here to see evaluation summary chart), combinations of pre-emerge followed by post-emerge herbicides demonstrated significant yield response. On average, those programs saw a 4-5 bu./ac. increase in yields (some were even higher).
The trial, which used a weedy check (no herbicides or weed control of any kind) and a weed-free check (hand weeded with no herbicides) showed a 50% yield loss in the weedy check, and a 65% yield gain in the weed-free check. A number of the pre followed by post herbicide trials showed gains that matched or exceeded the yields of the weed-free check (see highlighted areas of this chart ) .
It boils down to this, Carlson explained: The cost of a complete herbicide program that includes both pre- and post-emerge herbicide applications is offset by the improved yield potential. The benefit is found in a solid return on investment.
"Start clean, stay clean," said Carlson. "Control weeds before they emerge or soon after to preserve yield potential." Plus, in a world of increasing weed resistance, a pre followed by post program can help manage the toughest weeds, such as waterhemp and giant ragweed.
"We have lots of options," he said (see article at right on one option, Flexstar GT®). Federated Agronomists are ready to help you find the right combination of products for your soybean weed management program. Contact your agronomist soon!
Be sure to attend a Soybean Grower Workshop where this will be a key topic.