-Farm News photo by Karen Schwaller
Waterhemp can produce thousands of seeds per plant, making it easy for them to quickly repopulate a field. ISU Extension officials say farmers are paying attention to their weed control programs overall, working hard to keep weeds under control.

CALUMET — Spray application was front and center on the weed management portion of the Northwest Research and Demonstration Farm Field Day and Weed Resistance Round Table, which took place earlier this month at the Northwest Iowa Research Farm south of Calumet.

Wesley Everman, assistant professor at Iowa State University and Extension weed scientist (Ames), said spray drift issues are becoming more of a topic.

“We’ve noticed a lot of off-target injury in corn and soybeans this year, such as Dicamba drifting on soybeans and Clethodim on corn, which is often added in to soybean (sprays) to help kill grasses and volunteer corn, and it’s drifting onto our corn fields,” he said.

Everman said northwest Iowa experienced one of the windiest springs on record, so seeing this happening didn’t come as a surprise. But he said as new herbicide labels come online, along with re-registrations of current products, there will be a lot more scrutiny and restrictions and rules around keeping spray in the field.

He said pre-emergent programs with residual activity can be helpful.

“It gives us flexibility on when we apply that post application so we’re not chasing the earliest (date) around rain and windy days to get our weeds sprayed,” he said.

He said hooded sprayers (with hoods over the nozzles) would also help, though they are an added expense to spraying. Also, nozzle technologies (such as drop nozzles) are available that feature drift-reduction properties, though Everman said strong winds could still result in drifting.

“Those are options we’re looking at and seeing how feasible they could be on a bigger boom, rather than on smaller equipment,” he said.

He added that with hooded sprayers, the majority of the spray goes directly over and onto the canopy, with almost no opportunity for spray to blow away.

Everman said the holdback on hooded spraying is the slower rate of speed and lower boom height needed for a good application.

“For anybody spraying, time is money — you might have only a certain amount of time to spray hundreds or thousands of acres, and the more time you take in each field, the fewer fields you’re able to spray, and the longer it takes to pay for that equipment,” he said.

Everman said the farm community in general will watch (and has been watching) in a more scrutinizing way moving forward as they work toward a more practical approach to keep spray where it’s supposed to be, when combined with the changes with the EPA herbicide strategy.

He said windy springs like northwest Iowa has been experiencing have put farmers and commercial applicators between a rock and a hard place — with wind slowing down the spraying process, while weeds grow potentially taller than a spray will be able to kill them. He said with wind not offering much (if any) break, many producers and applicators went ahead and sprayed, hoping there wouldn’t be too many issues as a result.

“Application timing is important,” stressed Everman. “If we spray foot-tall weeds with Liberty, Enlist, Dicamba — we aren’t going to get good control, especially if it’s waterhemp. So we want to make sure we’re spraying small weeds, and that’s where that pre-emergent herbicide (with residual activity) will help because it offers more flexibility in being able to spray later.”

Grasses, broadleaves, waterhemp

Everman said he’s been seeing more grasses and broadleaves (waterhemps, grasses, etc.) surviving various herbicides during the early- to mid-June applications.

“If you notice weeds coming through, get out there and scout after you spray and see what’s there and if it’s dying, and give your Extension people a call,” said Everman.

He said together they could help figure out if the cause of weeds emerging is a result of weather, application or something potentially going on with resistance. He said weather has been a big challenge this year, with too much or not enough rain in areas, and humidity playing a factor.

Everman said waterhemp issues continue to exist, but he said in general he sees a lot of clean fields, with no waterhemp showing.

“It tells me that people are paying attention to their programs,” he said. “But we are seeing resistance to a number of different modes of action, and we have some populations we’re investigating that have survived sprays that they don’t have resistance to. We just need to be vigilant.”

Everman said he will conduct a statewide survey this fall, where he will collect seeds from various fields where waterhemp is surviving to try to determine where the resistance level is and what herbicides may actually be on the right track. He said previous people in his position have identified five layers of resistance to waterhemp.

Everman said waterhemp is one of a few resistant weeds that produce several thousand seeds per plant, so he said one survivor can repopulate a field. He said plants like that also have high genetic diversity — especially waterhemp, palmer amaranth, and Italian rye grass — making the process of killing those weeds complicated, since the seeds/weeds are all so genetically different and thrive (or die) under all different kinds of weather variables, too.

He said waterhemp is a weed that might take several modes of action to try to control. Some may germinate early in the year, which can be taken out with tillage. But others wait until late July, so tillage would not work.

“Genetic variability throws a wrench into the whole program,” said Everman. “But in general, if our weather is right and we time our herbicides right, we see effective control 99.9 percent of the time, and in those very few other instances, we investigate for other things like resistance or something else. But we can solve a lot of our challenges with the right time and the right weather — and yet, those are two big things we can’t control.”

He said once waterhemp gets six to 10 inches tall, there are not a lot of herbicides that are effective.

“If we wait until we get a window to spray, we don’t get satisfactory control in that kind of situation, but we’re going to spray because we can’t let those weeds go,” said Everman. “It’s always playing catch-up, and we have to look at repeat applications and hoping the crop gets to canopy to help suppress what’s left,” he said.

He said agriculture is on the front end of new technologies for more precision spraying, such as drone application, sprayers that only squirt when they “see” a weed, laser technologies, and electrical weed zappers.

The future of Dicamba for soybeans, he said, is now in the hands of the EPA, with many companies applying for the label. He said there are many variables to consider before putting it back on the market, and that “time will tell.”

Everman said genetic weed research has taken a solid hold in just the last decade or so, adding that there hadn’t been an urgent need until recently. He said there is much left to be learned, but in the meantime, he said the main issue of drift needs to be controlled right now.

“We don’t want drift to happen, so we just need to pay attention and follow some of these rules a little more,” said Everman. “I think it’s going to change the way we make some of our applications, and there will be some growing pains around that because it won’t necessarily be business as usual.”