“Sonic ® [with its two modes of action] at a rate of 3.2 to 5 oz./ac. is a lead recommendation for us where waterhemp and Giant ragweed are an issue,” said Kevin Carlson, Federated’s senior agronomist (see Sonic fact sheets).
For more residual control of waterhemp, “tank mix Blanket ® at a rate of 2-3 oz./ac. with the low-use rate of Sonic at 3.2 oz./ac.,” said Carlson (see Blanket fact sheet). But, he said, “there is one ‘watch-out’ . . . and that is the ALS-resistant giant ragweed.”
“We see reduced control in areas that have populations of ragweed that are resistant to ALS chemistry. One of the active ingredients in Sonic is an ALS chemistry so we see reduced control.”
To combat this issue, he said, Federated recommends a tank mix: Add Tricor ® (or metribuzin) at a rate of 6-9 oz./ac. (see Tricor fact sheet). Liquid Tricor helps with ragweed control, pre-emerge, Carlson noted. Use the lower rates on lighter textured and lower organic matter (OM) soils.
Contact your Federated Agronomist with questions about these tough-to-control weeds, and make plans now to prevent giant ragweed and waterhemp from becoming an insurmountable issue in 2018.