Chemical resistance threatens global cotton

Herbicide resistance in weeds is a growing threat to global cotton production. Amid technological advances, farmers face increasing challenges in controlling resistant infestations. A recent study reviewed international data and scientific literature, highlighting trends and proposing solutions.

Since the first case was recorded in 1973 in the United States, involving Eleusine indica resistant to trifluralin, 119 cases occurred until 2020. More than 76% of them occurred in the USA. Since the 2000s, there has been a significant increase in occurrences. Among the main resistant species, the following stand out: Amaranthus palmeri, Amaranthus tuberculatus e Xanthium strumarium.

Among the grasses, Eleusine indica e Sorghum halepense are the most common. Most cases involve resistance to glyphosate (HRAC-9 Group) and ALS inhibitors (HRAC-2 Group). Herbicides that affect microtubule assembly (HRAC-3 Group) and ACCase inhibitors (HRAC-1 Group) also appear frequently.

The cases are concentrated in regions with intensive use of herbicide-tolerant genetically modified cotton. In the US, farmers often rely exclusively on glyphosate. This practice, combined with the lack of active ingredient rotation, has favored the emergence of resistant biotypes.

The most resistant species

Amaranthus palmeri It is the most resistant species, present in almost half of the cases involving glyphosate. Its rapid growth, high seed production and dispersal facilitated by agricultural machinery and migratory birds contribute to its proliferation.

Dioecious species, such as this one, favor crossing and genetic variability, accelerating the evolution of resistance.

Measures to contain the problem include rotation of cropping mechanisms, use of residual herbicides, cultural practices such as minimum tillage and the use of mulch, and manual or mechanical techniques. The adoption of precision agriculture technologies, such as localized applications with sensors and drones, is also recommended.

Herbicides with different modes of action applied in mixtures have the potential to delay the emergence of resistance. However, high costs limit their adoption. Even with new technologies such as dicamba-tolerant cotton and 2,4-D, overdependence could repeat the cycle seen with glyphosate.

More information at https://doi.org/10.1016/j.cropro.2025.107320