For better or worse, throughout many regions of the country 2015 provided the optimal growing season conditions for both crops, as well as unwanted invasive weed species, making the past few months ideal for evaluating the effectiveness of different weed control strategies.
Neil Schumacher, Central Valley Ag (CVA) (Oakland, NE) agronomy sales manager, says the two largest challenge weeds in his three state territory have been Roundup resistant marestail and waterhemp.
“Those two continue to express more resistance to Roundup and become more and more of a challenge each year,” he says. “We have other weed species that have some amount of resistance to Roundup throughout the state but those two seem to be the most prevalent and the most difficult for us to manage.”
The management strategies his team recommends to CVA growers to eradicate these weeds, according to Schumacher, is an always moving target.
“It’s been an evolving challenge for us, and we’ve promoted residuals and we’ve promoted fall applications for marestail,” says Schumacher. “And it’s like anything else; if you don’t see it in your own fields you assume it’s not really a problem for you.
“This year has really pronounced itself with both of those weed species just being more difficult than normal; we’ve had a lot of rain and a lot of good growing conditions for weed species. We’ve definitely gained some traction (in addressing the problem) but it’s been a challenge because Roundup was so easy for so many years, guys enjoyed that … and the cost was less expensive.”
Schumacher adds that many challenges remain for growers still grasping with the new post-glyphosate era of weed control.
“Roundup still works on some fields, but then you go to the field next door and it doesn’t work at all,” he explains. “So it’s always frustrating for growers to have the option of spending a lot less money on Roundup only then have to spend $15 to $20 more per acre on the other fields where glyphosate won’t work. So one of our big challenges has been helping the growers look at the risk and the cost of not managing it upfront vs. trying to battle both of those weeds post-season.”
Another challenge that has arisen with CVA’s altering of their herbicide resistance management plans is a shrinking window of opportunity with fall burndown applications, according to Schumacher.
“Those guys are in harvest and then any fall tillage that they might do, and we’re into our fall soil sampling program and fertilization applications, so the challenge for the herbicide program is preferably the soil is only 50 degrees or less so we don’t break that product down too much in the fall before it has a chance to work for us in the winter and into spring. That doesn’t really leave a wide window of time for us.”
Now, with the days of a one-time glyphosate application lasting the entire season long in the rearview mirror, Schumacher thinks CVA’s spring pre-emerge applications are “the fastest growing segment” of the herbicide program at the No. 13 CropLife 100-
“At least throwing in a pre-emergence with a residual, and the second step of that would be getting them to run at recommended rates instead of reduced rate (to save a little money), or at least look at coming back with a post application because both of these weed species are difficult to manage in a post-arena.”
Schumacher says he’s still seeing “a lot of water hemp poking up through soybeans” and that both the Liberty Link soybean systems and the coming dicamba and 2,4-D tolerant cropping systems “pose a lot of interest” in CVA’s trade area.
“If the dicamba is truly more manageable than it’s been in the past and doesn’t cause a lot of issues with drift and off target movement, that will probably be the one with the most potential for our guys,” Schumacher says.
Crop Protection Perspective
Valent U.S.A.’s John Pawlek, product development manager, says the company’s herbicide resistance management strategy that it recommends to growers, starts with always maintaining a full label rate of residual herbicide.
“Then the second part of that is to make sure we get the weeds when they are most easily controlled, which is at the seed or seedling stage of growth,” Pawlek continues. “And with the spread of resistant weeds continuing at a prolific pace, we also always recommend using multiple effective modes of action.”
Valent’s current anti-weed arsenal in soybeans includes Valor SX, Valor XLT, Fierce and Fierce XLT, according to Pawlek.
“In situations where there’s low weed pressure and no known history of resistant weeds, we recommend Valor SX (flumioxazin), and where we see a need to control larger seeded broadleafs and want a longer residual effect, we can go with Valor XLT (flumioxazin + chlorimuron-ethyl),” he says.
When resistant weeds enter the picture, Fierce (flumioxazin + pyroxasulfone) and Fierce XLT (flumioxazin + pyroxasulfone + chlorimuron-ethyl) are the main options depending on the circumstance.
“Fierce is great where the grower is running into annual grasses and resistant Palmer Amaranth and waterhemp — it’s two modes of action can both control that weed spectrum — and Fierce XLT is where you’re kind of bringing out the big guns with three effective modes of action. We’ve had great success with this approach.”
According to Pawlek, weed extension specialists have a three step approach to managing glyphosate, ALS or even the recently confirmed PPO resistance in soybeans.
“Academia has been very adamant about taking a three step approach: the first step is using a full rate of the residual herbicide in preemergence, then using multiple effective modes of action and finally use an overlapping residual with your postemergence application,” explains Pawlek.