weeds in soybean field Jeff Nagel, Ceres Solutions Cooperative
WORTH FIGHTING: Even this many weeds in a field can hurt yield, and the seeds they produce can add to future headaches. Note different types of weeds are present.

Win the war on weeds starting this year

Understand the principles of weed resistance and manage accordingly.

By Allie Abney and Morgan Hasler

You may feel like you are at war with weeds. If you were preparing to go to war, you wouldn’t fight alone, with your worst sword, and you definitely wouldn’t want to have only one weapon of defense. You and farmers across Indiana are constantly battling weeds due to the increasing amount of herbicide resistance in weeds.  

“It isn’t herbicides that create herbicide-resistant weeds,” says Bryan Young, a botany and plant pathology professor at Purdue University. “Instead, the culprit is how we use herbicides in an overall weed management strategy. To preserve the effectiveness of herbicides, it is imperative that we become better stewards of their use. Minor changes made today can avoid costly problems in the future.”

Weed resistance is a rapidly escalating problem that defies easy solutions, Young says. The battlefield is growing larger as marestail, giant ragweed, Palmer amaranth and waterhemp have become resistant to herbicide. Since the 1990s, when Roundup Ready technology was introduced, farmers have used Roundup herbicide as their preplant burndown and postemergent treatment.

Roundup made it easy for farmers to manage weeds efficiently, Young notes. It was quick and simple, but the weeds adapted to it. There is no longer a “silver bullet.” By 2006, Palmer amaranth started showing signs of resistance to Roundup, and in 2012, resistant weeds were found in northwest Indiana. By 2014, Roundup postemergence applications were not killing every waterhemp plant. Fields started to look less clean, and waterhemp started to scatter, Young says.

In 2015, fields became a muddy mess as farmers faced heavy rains throughout the summer. Waterhemp from previous years went to seed and exploded. Unfortunately, the weeds quickly multiply, whether they are spread via water, birds or combines, Young says.

To make sure you don’t move remnants of the past field with them, it is incredibly important to clean out combines between weed-infested fields. As growers look to 2018, Jeff Nagel, Ceres Solutions Cooperative director of agronomists, says, “Waterhemp is my biggest concern due to its ability to have resistance.”

No easy fix
There is not one easy fix for this problem, but there are recommended techniques in order to be proactive in this ever-changing war against weeds. Bill Johnson, Purdue Extension weed control specialist, recommends four easy steps to help Indiana farmers.

“First, farmers need to pick their battles,” he says. “They need to determine what weeds will be most problematic, and plan a unique strategy for each field — rather than rely on a solution-for-all-fields approach.”

Additionally, it’s important farmers understand their capabilities, Johnson says. It’s essential to do things right the first time, because rescue weed control operations are rarely successful. Farmers must make sure they have the correct tillage equipment, money to invest in the crop herbicide-resistance trait and an understanding of what is feasible for their situation.  

Once the problem is identified and the farmer understands his or her capabilities, it is vital to have at least two modes of action for each of the worst weed problems in each field, Johnson insists. To fight weed resistance, farmers must diversify their herbicide programs and tillage practices, and follow the specific herbicide label directions.

The last recommendation is to pay attention to the little things like adjuvants, timing, weed size and crop growth stage restrictions, and make sure to follow the suggested timing, weather conditions and nozzle recommendations, he says.

Nagel explains that through multiple herbicide sites of action, farmers can win this war. He recommends that farmers till their fields or use a burndown herbicide to target marestail in the fall. In the spring, at or near planting, these steps should be repeated to allow crops a weed-free environment in which to grow.

After planting, it’s important to spray small weeds that are less than 4 inches in height. Additionally, late-germinating weeds need to be sprayed with a layered or in-season residual herbicide with the post application, he says.

The last precaution Nagel gives is to clean equipment as you move from field to field so you don’t spread weed seeds.

Make the investment
“Farmers have to do what is right when it comes to fighting weed resistance, and it is an investment on the crop, but this is not an area to cut corners,” Nagel says.

If a person were preparing to go to war, it’s common sense that he or she wouldn’t take their worst sword. This is important for farmers to remember when entering fields with weeds trying to rule the land, Nagel says. With residual herbicides, the cheapest application may be cost-effective, but may not be a high enough rate to fix the problem. Many times, the most cost-effective option doesn’t control the weeds completely.

There are also other options for farmers to control weeds besides their herbicide residual programs, Nagel says. One of these alternative actions is to change row spacing. When rows are closer together, it creates a quicker canopy, allowing the crop to dominate the sunlight. Another is to diversify crops from year to year.

“You won’t win this battle in a year,” Nagel says. “But by focusing on each individual field as if you’re fighting a handful of mini battles, the issue will become a lot more manageable for years to come.”

Each battle may need a different weapon for victory, as the enemy may react differently to the tactics used. As the war on weeds continues to grow, there is a job to be done, Nagel says. The war will not be won overnight, and it’s up to farmers to properly fight the individual battles within each field.

Abney and Hasler are seniors in the Purdue University Ag Communication program.

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