Weed Control in Corn: Inside the Growing Threat of HPPD Resistance
January 19, 2026 Herbicide resistance is no longer a distant concern for corn growers. It is already influencing weed management decisions across much of the Corn Belt. According to Josh Putman, Technical Marketing Manager at BASF, early indicators of resistance to HPPD herbicides are appearing in fields — even if they are not always immediately acknowledged.
“Farmers know resistance is occurring,” Putman said. “But many won’t acknowledge it until they’re seeing 30% weed control failure or more.” He likens the situation to a baseball pitcher throwing the same pitch repeatedly. Eventually, the batter adjusts — and weeds have done the same.
Shifting Weed Populations Drive New Challenges
For decades, weed control in corn was relatively straightforward. That began to change as resistant species emerged and innovation slowed. While new modes of action once entered the market roughly every five years, Putman noted it has been more than 25 years since a truly new site of action was introduced.
At the same time, weed populations themselves have shifted. Species such as Palmer amaranth and waterhemp — two aggressive, dioecious pigweeds — now dominate many fields. Because male and female reproductive structures occur on separate plants, resistance traits can spread rapidly through pollen transfer. Under favorable conditions, these weeds can grow more than an inch per day and produce more than one million seeds per plant.
“We’re starting to lose knockdown efficacy with some of the earlier HPPD chemistries,” Putman said. “That’s a clear signal that resistant populations are present.”
Environment, Timing, and Pressure Matter
Putman cautioned that not every control failure is the result of resistance. Environmental and agronomic factors, including dry conditions, delayed applications, or weeds that are too large at the time of spraying, can also compromise performance.
“If we don’t get activating rainfall on a pre-emerge herbicide, that puts a lot more pressure on post applications,” he said. “That’s why it’s critical to start with a strong residual pre and then layer residuals into post-emerge applications.”
The objective, Putman explained, is to control weeds at their weakest stage — before emergence — when they have only one growing point. Once weeds reach several inches in height, multiple growing points make control significantly more difficult.
Rethinking Programs: Start Clean, Stay Clean
As traditional herbicide programs lose effectiveness against tougher weeds, Putman emphasized the importance of proactive management and diversification.
“Weed scientists have been saying this for years: start clean and stay clean,” he said. “That means diversifying sites of action and layering residuals throughout the season.”
BASF’s approach focuses on building programs that address weeds early and maintain pressure throughout the season. Putman pointed to Surtain® herbicide, a newer site of action for corn that can be applied from early pre-emerge through early post-emerge, as a foundation product. Additional residuals and post-emerge tools can then be layered to extend control.
“When you build a full program, you can put seven different sites of action against weeds,” he said. “You’re really throwing the kitchen sink at them from a management standpoint.”
Stewardship Starts with Scouting
Preserving the effectiveness of HPPD herbicides and other cornerstone chemistries ultimately comes down to stewardship, and Putman emphasized that scouting remains one of the most important tools available.
“Boots-on-the-ground scouting is extremely important,” he said. “That includes early-season scouting, mid-season checks, and even riding in the combine at harvest to evaluate how your program performed.”
While modern tools such as yield monitors, drones, and precision technology can support scouting efforts, Putman stressed that mindset matters just as much. “What we do this year affects next year,” he said. “Ask yourself: what’s one thing I can do differently to improve weed control next season?”
Preventing weeds from going to seed remains a central goal. With species such as Palmer amaranth capable of producing massive seed banks, the consequences of poor control can persist for years.
Looking Ahead
As resistance pressures intensify, BASF continues to invest in research and development across crop protection products, seed traits, and emerging technologies. Several new products are currently awaiting EPA registration, with additional details expected at upcoming industry events such as Commodity Classic.
Putman summarized BASF’s message with a few core principles: start clean, control weeds early, scout consistently, and diversify sites of action.
“If we can prevent weeds from going to seed,” he said, “we’re protecting not just next year’s crop, but the long-term productivity of the field.”
As always, Putman encouraged growers to consult their local BASF representatives or visit agriculture.basf.us for more information.
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