All weeds threaten corn and soybean yields by robbing plants of vital nutrients and water. But not all management programs control weeds effectively, leading to escaped weeds and future generations of weeds in the field. Among the toughest weeds to control, Palmer amaranth and waterhemp are two species no grower wants in his or her field.
As prolific seed producers, Palmer amaranth and waterhemp wreak even greater havoc in growers’ fields, because when seeds fall into the soil seed bank, growers can expect for those weed species to appear in their fields during the next growing season. And because these weeds have confirmed resistance to a variety of popular herbicides, growers struggle more each year to find a management program that controls these weeds effectively.
Many growers across the Midwest saw escaped Palmer amaranth and waterhemp in their fields this year. And while some growers believe one or two escaped weeds isn’t much of a threat, experts insist that one escaped weed is one too many.
According to a Purdue University study, one waterhemp plant can produce up to 1 million seeds. When seeds from escaped waterhemp plants go into the soil seed bank, those fields will have waterhemp infestations for future seasons.
Control weeds before they go to seed
“That’s why it’s critical for growers to manage the weeds before they deposit seeds into the soil seed bank,” explains Dean Grossnickle, agronomy service representative for Syngenta. “By understanding the historical weed pressures in the field, growers can develop a customized management program and control weeds before they threaten yields.”
But even if growers use a robust herbicide to help control weeds in the field, other management practices need to be considered to effectively prevent weeds from infesting more fields. Many carriers, including poorly cleaned field equipment, water runoff, wind and animals are factors that contribute to the spread of weeds like Palmer amaranth and waterhemp in the field.
Grossnickle says, “Managing those tough-to-control weeds is a whole-farm approach, so growers should consider cultural practices in the field to ensure their fields start clean and stay clean, season-long.”
Use effective burndown, preemergence residual
All hope isn’t lost when it comes to preventing weed escapes. Experts recommend growers start the 2018 season with an effective burndown and a preemergence residual herbicide application. “Hitting the weeds before they emerge is key to keeping them at bay,” says Dane Bowers, herbicides technical product lead at Syngenta. “Acuron and Acuron Flexi corn herbicides contain bicyclopyrone, the newest herbicidal active ingredient that delivers more powerful weed control.”
Soybean growers can use Gramoxone SL 2.0 for burndown followed by an application of BroadAxe XC or Boundary 6.5 EC herbicides. These preemergence herbicides, along with Acuron and Acuron Flexi, contain multiple effective modes of action and active ingredients, which are critical components to managing weeds effectively. “By using the full, labeled rate of a preemergent residual herbicide, growers control weeds before they have a chance to emerge in the field. And this also delays the onset of resistance,” says Bowers.
Other factors, including cover crops, mechanical weed control and crop rotation, are tools to ensure growers are attacking weeds from all angles. “While growers may have seen escaped weeds in 2017, implementing a series of management practices will help prevent weed escapes in 2018,” he adds.