Three Herbicide-Resistant Weeds to Watch in 2024

The number of weed species resistant to some of the agricultural industry’s most popular herbicides continues to grow. According to statistics, there are more than 361 weed species globally that show resistance to common herbicides such as glyphosate – 180 in the U.S., impacting such crops as corn, soybeans, cotton, and sugar beets.

By now, most folks in the agricultural world are familiar with the most troublesome resistant weeds typically present across the nation’s crop fields. These include the usual suspects – giant ragweed, marestail, waterhemp, and Palmer amaranth. But in 2024, crop protection supplier representatives that spoke with CropLife at the 2024 Commodity Classic show in late February in Houston, TX, mentioned a trio of lesser-known weeds that could cause resistance headaches, this year and beyond. The first of these is kochia.

Already a problem across many of the crop fields in North Dakota and other Western states, kochia is an annual herbaceous plant with a deep taproot that can grow to 1.6 to 4.9 feet tall. According to Will Griffin, Row Crop Segment Manager at Valent USA, there are more than 50 counties in North Dakota where kochia has confirmed resistance to dicamba and glyphosate.

“Kochia is definitely a weed for growers to keep an eye on this year,” said Griffin. “It’s probably only a matter of time before this weed spreads even further throughout the upper Midwest.”

Another weed also primed for more herbicide resistance is common ragweed. According to Camille Lambert, Technical Service Manager at FMC Corp., common ragweed has typically been overshadowed by its giant cousin when resistant weeds are discussed. “Right now, common ragweed is resistant to more herbicides than giant ragweed,” said Lambert. “It has documented resistance to ALS inhibitors, PPO inhibitors, and atrazine.”

The third potentially troublesome weed to watch in 2024 is Italian ryegrass. Similar to perennial ryegrass, Italian ryegrass can be found throughout the U.S., but has been showing signs of resistance most in the South, said Shawna Hubbard, Strategic Marketing Manager for Corteva Agriscience. “Italian ryegrass has resistance to both Group 1 (AACase inhibitors) and Group 2 (ALS inhibitors) herbicides,” said Hubbard. “And the problem of controlling it is spreading, with many growers now actively looking for new active ingredients to fight Italian ryegrass.”