Even if you applied a pre-emergent herbicide this year, even if you got out a burndown application, it’s critically important to stay vigilant on weed control. In some areas, heavy rains significantly shortened the lifespan of many preemergent herbicide applications. In other areas, there wasn’t enough moisture to gain timely activation.
When you take those factors into account, this won’t be a season to put your weed management on autopilot.
Weed scientists like Purdue’s Bryan Young caution growers to watch for weed flushes and make timely treatments. If problems arise, act quickly. Don’t assume that you can simply come back with a salvage treatment later.
“The best return on your dollar invested for corn or soybean weed management has been with early-season weed management,” he points out. “Why invest later in the season when the return isn’t as good?”
“During winter meetings and talking with growers, they’re always saying, ‘Well, commodity prices are down, I really don’t want to spend a whole lot more in herbicides but I know I need to improve weed control.’ I tell them that if you want to cut out anything for weed management, cut out the rescue treatments in the late season,” Young says.
“Rescue treatments cost the most. Also realize that any weeds you have to deal with late in the season have already robbed you of some yield as well,” Young advises.
“Do everything possible to control weeds early and keep them controlled. Once the weeds gain an advantage, that’s when we lose, especially where glyphosate isn’t a viable option because of weed resistance. When the weeds get too big we can’t get the yield back and we can’t get the weed control back, either. ”
The graphic above from Young’s presentation, Proactive Weed Management, illustrates that using pre or residual herbicides consistently leads to greater waterhemp control and delivers more yield. But timing of the post emergence application that includes a residual herbicide is just as critical as earlier season applications.
“If you have a lot of vegetative cover (ie., weeds and/or crop) when you make that post emergence application, all that foliage will intercept at least some of your spray,” he explains.
“Any residual herbicide that doesn’t reach the soil isn’t going to give you good weed control. If you’re going to use a post emergence herbicide, try to spray before plants have more than three trifoliates. I’d say you don’t want more than 50% canopy closure by the time you’re spraying your post emergence residual. Anything more than that and the majority of the herbicide is sitting on the leaves and not getting where you need it to be.”