The only issue concerning weed control as soils dry out and farmers consider getting back in the field isn't if they can plant soybeans behind a corn herbicide. The official answer to that one offered by Purdue university weed control specialists is no, unless the herbicide was Prowl, Python or some other herbicide that allows it on the label. The specialists say that otherwise, labels have plant-back restrictions that mean you can't come back with soybeans in the same season and still be on label.
The other situation looming is what to do with big weeds. Even farmers who didn't experience flooding in some cases have been sidelined from even spraying for two to three weeks or more. In fields where they intended to apply postemergence weed control in corn, especially, rank weeds could become an issue.
If it's Roundup Ready corn, you've got a leg up. But still don't approach it as business as usual, advises Glen Nice, Purdue University weed control specialist. "We almost always recommend going out with the full rate of glyphosate in the beginning, even in normal situations," he says. "We definitely would recommend going with the full rate now."
Two of the harder weeds to bring down in any season are giant ragweed and common lambsquarters. The secret to good control with these two weeds is often catching them while they're small. If you've got fields that couldn't be sprayed on time, you're no longer looking at size as a tool in your tool kit to control these weeds. Instead, it's likely working against you. Once the weeds have any size to them, they become more difficult to bring down.
"Your best bet is to gear your herbicide mix to whatever the toughest weed is in the field you're going to spray," Nice says. "Use the rate of the right product that should bring down that weed when you're deciding what to put in the tank."
This situation may call for adding additives or mixing in other herbicides just to help get control of the toughest weed, say giant ragweed. It's certainly not business as usual.
One other situation farmers should watch for after flooding is weeds appearing in fields that they've claimed up over time, Nice adds. "Unfortunately, flood waters can leave weed seeds behind," eh says. "You may wind up with a new flush of weeds in fields that haven't given you many problems in a long time."
Then there's always the 'glass is half full' side, he notes. Maybe along with killing off corn or soybeans, flood waters, especially ponded water, also killed off the weeds, Nice concludes.