If you thought the days of cutting weeds out of fence rows or drainage ditch banks ended with better control of johnsongrass and shattercane, think again. Palmer amaranth is in at least eight Indiana counties, and likely more. It's a member of the pigweed family, but if redroot or smooth pigweed is a match, Palmer amaranth is the flame.
Dill Johnson, Purdue University weed control specialist, says the best way to stop it is to use prevention. In some cases that may be using residual herbicides for early control on a soil-applied basis, whether you know you have it or not. The fact is that the same treatments that would help knock down Palmer amaranth will also knock down waterhemp. Palmer amaranth has been identified in a few counties, waterhemp has been documented in about a third of the state.
The secret for scouting is to distinguish it from redroot or smooth pigweed, or even waterhemp early. Learn the characteristics of small plants. Study photos so if you see it in the field, you'll know what you're up against.
The problem with waiting for post applications, notes Mark Lawson with Syngenta, is that is you don't get it by four inches tall, you're likely not going to get it with a post spray. Farmers notoriously underestimate the size of weeds while scouting. In this case, four inches means four inches, he says. After that, it's likely over as far as stopping it during the season with chemical control.
Johnson says a good practice is to be vigilant and scout ditch banks, grass waterways, the edge of fields and other areas as the season progresses. If you find Palmer amaranth, cut it out. The best policy is to remove it and destroy it off site. The weed has the ability to regrow, even if it's cut off, if it's left lying on the ground.