“We learned a lot about weed control in 2019,” says Bill Johnson, Purdue University Extension weed control specialist. “What we saw last year reminded us of several key issues about weed control. Growers will need to address those in putting together weed control strategies for 2020.”
Johnson hopes 2020 won’t be like 2019, but issues that surfaced in 2019 should be addressed.
Here’s a closer look at key issues. Incorporate these ideas into 2020 weed control plans.
ATS affects burndown herbicides. Purdue agronomists Bob Nielsen and Jim Camberato find significant returns for sulfur on some soils. ATS is a cheap source. “The problem is that if you add it into your herbicide burndown application, it can cause antagonism with certain herbicides,” Johnson says. The primary problem is with grass weeds or grass cover crops, he notes.
If you’re going to apply ATS, increase herbicide rates and seek the best conditions for spraying. “If it’s cool and cloudy and you’re spraying reduced rates of glyphosate, it will likely be an issue,” Johnson says.
Cover crops can escape. If you take products out of the mix to save on costs, you may risk incomplete termination of cover crops, Johnson says. There aren’t a lot of good options for taking out cover crop escapes once the cash crop emerges. Do things right and get them the first time, he advises.
Drift concerns still exist. Early in the season, the Office of Indiana State Chemist gets drift complaints for products such as Sharpen, glyphosate and 2,4-D. In 2019, the amount was normal — 30 to 40. Later, dicamba drift complaints piled up. OISC received around 250 total complaints last year, and that was more than in 2018. Physical drift still accounts for several complaints. The cause of most dicamba complaints in 2017 and 2018 went down as “undetermined,” with 2019 complaints still under review. About 95% of all dicamba complaints are on sensitive soybeans.
The cutoff date for dicamba applications in 2020 is June 20. That’s a firm date. Anyone caught applying after June 20 could face a six-month suspension of their applicator license, Johnson reports.
Enlist, which includes 2,4-D choline, can still cause drift if label guidelines aren’t followed, he notes. Be especially careful around sensitive crops.
Make post applications to small weeds. Applying most postemergence products on weeds 4 inches tall or smaller is critical, Johnson says. If you don’t fully kill weeds on the first pass, resprays won’t be completely effective. Waterhemp plants that aren’t killed the first time because they were too tall send out axial buds and regrow.
“You’re better off spraying early, even if you have to spray a second time for late emergers, than waiting and trying to get everything at once if you have weeds like waterhemp,” Johnson says.
Enlist will be an option in 2020. Seed sales reps say nearly every bag sold will be Enlist E3 soybeans. Still, Johnson advises making sure. Enlist One soybean seed isn’t tolerant to glufosinate, the active ingredient in Liberty. Enlist E3 beans are tolerant to 2,4-D, glyphosate and glufosinate.
Enlist One herbicide is 2,4-D choline only. Enlist Duo also contains glyphosate. Check the label for each herbicide to see lists of approved tankmix partners and spray nozzles. You will also find information on the required buffer for sensitive crops and wind speeds. These requirements are different than for dicamba-tolerant soybean herbicides.