02 Jun #Grow15: Weed Management Focus of Rochester, Minnesota Field Day
Reference: http://www.agriculture.com/crops/pesticides/herbicides/grow15-weed-magement-focus-of-rochester_179-ar49487
The University of Minnesota has several research sites where farmers can evaluate different weed control programs. The particularly challenging weed at the Rochester, Minnesota site is giant ragweed.
“Giant ragweed is truly our main concern,” says Lisa Behnken, Extension educator at the University of Minnesota. “We have quite a population here, and it puts all herbicides to a very good test.”
Both giant ragweed and waterhemp have been producing big challenges for farmers as they continue to develop resistance to multiple sites of action. The research site allows Extension specialist to show farmers firsthand how well different preemergence and postemergence herbicides maintain control of weeds in corn and soybean systems.
“The goal here is to show folks how these different systems work,” adds Behnken.
Weed control in corn
There are more choices for weed control in corn than soybeans. “We have a lot more choices with site of action to control giant ragweed,” says Behnken. “We really try to focus on preemergence programs.”
The correct preemergence herbicide can allow for a longer window of opportunity for the postemergence applications. It also cuts the workload for the postemergence program. If weeds aren’t controlled at the 2- to 3-inch height, the result will be yield loss.
“You’ve got a window to try and control all your weeds in corn, postemergence, with 2- to 3-inch weeds, most farmers can’t do that,” explains Behnken.
That preemergence herbicide application can get your first flush of weeds and allows you to come back with a good post program. If you need to spray weeds larger than 3-inches tall, you can still kill them, but you’ve already lost yield. You just don’t realize it, says Behnken.
“If I have a really tough field, I want to get those big hitters that can carry my weed control longer to give me a longer window for my post,” says Behnken. “But also, if I can take that preemergence and control 80% of my weeds, now my postemergence doesn’t have as big a job to do anymore.”
“The bottom-line is to diversify herbicide use,” says Jeff Gunsolus, Extension weed specialist at the University of Minnesota. “Total postemergence systems create a problem with the time of weed removal. “
Weed control in soybeans
Around 90% of farmers used to have a total postemergence herbicide program for soybeans, but now they have to take a step back, says Behnken. With resistance issues, there are no longer as many tools in the toolbox.“With resistance, we’re now going back in time, saying we have to get a pre down,” adds Behnken. “Some of those pres cause a little bit of injury, but those preemergence herbicides take out those first flushes, give us another site of action, and come back with a timely post emergence application to finish the job.”
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