Euphorbia heterophylla herbicide resistance in Paraguay 2026: Multiple resistance to ALS, PPO and glyphosate raises concern

The global challenge of herbicide-resistant weeds continues to intensify, with the latest entry into the international resistance database highlighting a new case from Paraguay. As of March 24, 2026, Euphorbia heterophylla, commonly known as wild poinsettia, has been officially recorded as exhibiting multiple herbicide resistance, marking another significant development in the ongoing evolution of weed resistance across key agricultural regions.

Emerging Resistance in Paraguay

This newly documented case originates from Paraguay, where Euphorbia heterophylla was first identified as resistant in 2026. The species has developed resistance across three different herbicide sites of action, making it particularly challenging for farmers to manage using conventional chemical control strategies. The weed is known for its aggressive growth in crops such as soybean and maize, and its ability to adapt quickly under selection pressure from repeated herbicide use.

Multiple Resistance Across Three Modes of Action

The confirmed resistance in Euphorbia heterophylla spans three distinct herbicide groups, indicating a complex resistance profile:

• Acetolactate Synthase (ALS) Inhibitors – HRAC Group 2 (Legacy B):

  These herbicides are widely used for controlling broadleaf weeds, but resistance in this group is among the most commonly reported globally.

• Protoporphyrinogen Oxidase (PPO) Inhibitors – HRAC Group 14 (Legacy E):

  PPO inhibitors are critical for managing resistant weed populations, and resistance to this group significantly narrows chemical control options.

• Enolpyruvyl Shikimate Phosphate Synthase (EPSPS) Inhibitors – HRAC Group 9 (Legacy G):

  This group includes glyphosate, one of the most extensively used herbicides worldwide. Resistance to EPSPS inhibitors is particularly concerning due to its widespread reliance in conservation agriculture systems.

Implications for Crop Production

The emergence of multiple resistance in Euphorbia heterophylla presents serious implications for crop production systems in Paraguay and potentially across Latin America. With resistance confirmed to three major herbicide groups, farmers may face increased costs due to the need for alternative herbicides, integrated weed management practices, and potentially reduced crop yields.