AG NEWS
AG NEWS

Preparing for 2017 Weed Challenges in Soybeans

  • Mar 06, 2017
Soybean Field
If 2016 was any indication, soybean farmers should be ready to combat tough weed competition in the coming season. Herbicide-resistant marestail, waterhemp, Palmer amaranth, kochia and some ragweed species were leading problems during 2016 in Midwest soybean fields (see state recaps below). 
 
With resistant weeds on the rise, a complete herbicide-resistance management program is needed to take control, starting with a clean field at planting. Other recommended steps include crop rotation, three effective modes of action, overlapping residuals, timely applications use of full-label rates for herbicides with complementary adjuvants. With similar weed issues reported in both corn and soybean fields, a holistic approach across all crops in a rotation is needed.
 
While farmers may consider planting the recently approved dicamba-tolerant soybean system, the new dicamba formulation only counts as one of the three modes of action needed. Another option is to plant LiberyLink® soybeans and then use Liberty® herbicide as an in-crop application. 
 
WinField United agronomists recently shared some soybean weed insights from 2016 in this Corn & Soybean Digest article. Highlights by state are below.
 
Illinois: Glenn Longabaugh says the biggest 2016 weed-control issues in Illinois soybean fields were tall waterhemp and Palmer amaranth. Because of resistance to multiple herbicide groups across Illinois, including Groups 2, 5, 14 and Group 9 (glyphosate), a comprehensive herbicide-resistance management strategy is needed for acceptable control in any system, including non-GMO soybeans, Longabaugh says.
 
Indiana: Pigweed species, in particular tall waterhemp and some Palmer amaranth, provided the greatest challenge for Indiana soybean farmers in 2016, says George Watters. Nearly 100 percent of the waterhemp and Palmer amaranth populations are now resistant to glyphosate (Group 9) and ALS (Group 2) herbicides. Several populations are also becoming resistant to foliar applications of PPO (Group 14) herbicides. To best combat these challenging weeds, Watters recommends that farmers use a comprehensive herbicide-resistance management program.
 
Iowa: Resistance to glyphosate and Group 14 herbicides caused the biggest waterhemp control problems in Iowa soybean fields during 2016, Ryan Wolf notes. The appearance of Palmer amaranth also had Iowa farmers closely monitoring their fields. Higher rates of preemergent herbicides along with metribuzin in preemergent tank mixes provided the best weed control success. Timely post-applications also performed well. 
 
Michigan: Roundup Ready®- and ALS-resistant marestail was the biggest problem in Michigan soybeans, says Allen Pung. In addition to a good preemergence herbicide program, many farmers are also considering either LibertyLink® soybeans or the new dicamba-tolerant soybeans for 2017. A light tillage pass can also be helpful, he advises.
 
Minnesota: Herbicide-resistant weeds, including tall waterhemp, giant ragweed and common ragweed, were the top weed challenges for Minnesota soybean farmers, reports Al Bertelsen. In addition to identifying resistant weeds early and using at least three effective modes of action, Bertelsen recommends timely applications of PPO herbicides when weeds are small for improved weed control in in 2017. Because PPO herbicides require more spray coverage than glyphosate does, he advises spraying at higher volumes and selecting spray nozzles that increase weed coverage.
 
Ohio: Joe Rickard reports that marestail continued to be a major problem for Ohio soybean farmers. Farmers who have been making two applications of glyphosate or using the same chemistry for the past several years may not be receiving the same control as they did five or 10 years ago and should review their treatment options. He recommends a fall treatment to clean up winter annuals, followed by an effective residual herbicide mixed with 2,4-D to control weeds prior to planting. Spring preplant applications are also a good control option.
 
South Dakota: Ryan Wolf reports that weed resistance continued to challenge South Dakota soybean farmers. In 2016, waterhemp resistance to glyphosate and Group 14 herbicides was more prevalent in soybean fields, especially when spraying was delayed due to weather conditions. Glyphosate-resistant kochia and marestail were also problems. Farmers who used higher rates of preemergent herbicides and added metribuzin to their preemergent tank mixes had the most weed control success. Timely post-applications also performed well. 
 
Wisconsin: Tall waterhemp was the biggest weed challenge in Wisconsin soybean fields during 2016, says Todd Cardwell. While this weed isn’t new, glyphosate-resistant varieties have become difficult to control and have spread dramatically. Planning ahead and designing a long-term program is the best way to combat weed problems in 2017 and beyond, he advises. Farmers can address glyphosate and triazine resistance by making sure that their weed control program includes products that are still effective on resistant species. Some of the older chemistries like metribuzin (Dimetric® DF 75% or Sencor®) have been effective on glyphosate-resistant waterhemp. 

For similar insights on corn weed challenges, click here.