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QUIK STATS (last updated Oct 09, 2025 )
NOTES ABOUT THIS BIOTYPE
Resistance to HPPD Inhibitors – A Rural Legend?
Authors: Christophe Délye & Séverine Michel
Institution: INRAE, UMR Agroécologie, Dijon Published in: Phytoma, No. 785, Sept–Oct 2025
Abstract Until now, resistance to HPPD-inhibiting herbicides had only been reported in a few isolated cases outside Europe. In France, however, poor control of weeds in maize fields has been observed for several years, suggesting possible resistance.
Study Greenhouse bioassays were conducted on Echinochloa crus-galli (barnyardgrass) and Digitaria sanguinalis (large crabgrass). Three seed lots of each species, collected between 2017 and 2023 from monitoring networks, were tested for survival after application of mesotrione (HPPD inhibitor). Results were compared to reference populations with no known resistance.
Results Resistance to mesotrione at the maximum authorized dose (150 g/ha) was confirmed in all six seed lots, and some even survived twice that dose (300 g/ha). Additionally, ALS inhibitor (nicosulfuron) resistance was identified in all Digitaria sanguinalis samples. These findings represent the first confirmed global cases of resistance to an HPPD inhibitor in both species, and the first HPPD resistance cases reported in Europe. The study highlights the urgent need to assess the prevalence of this resistance in France.
Keywords: Maize, HPPD inhibitor, Echinochloa crus-galli, Digitaria sanguinalis, mesotrione, ALS inhibitor, nicosulfuron.
Experimental Details
Acknowledgments: Thanks to field collectors and contributors to the Ecophyto II and R4P surveillance networks.
References
ACADEMIC ASPECTS
CONTRIBUTING WEED SCIENTISTS
ACKNOWLEDGEMENTS
BACKGROUND Crabgrass (Digitaria sanguinalis) is an annual monocotyledonous weed. In recent years, field applications of nicosulfuron have been ineffective in controlling crabgrass populations in Shandong Province, China. To investigate the mechanisms of resistance to nicosulfuron in crabgrass populations, the acetolactate synthase (ALS) gene fragment covering known resistance-confering mutation sites was amplified and sequenced.
RESULTS Dose–response experiments suggested that the resistant population SD13 (R) was highly resistant to nicosulfuron (resistance index R/S = 43.7) compared with the sensitive population SD22 (S). ALS gene sequencing revealed a Trp574Arg substitution in the SD13 population, and no other known resistance-conferring mutations were found. In vitro ALS enzyme assays further confirmed that the SD13 population was resistant to all tested ALS-inhibiting herbicides. The resistance pattern experiments revealed that, compared with SD22, the SD13 population exhibited broad-spectrum resistance to nicosulfuron (43.7-fold), imazethapyr (11.4-fold) and flumetsulam (16.1-fold); however, it did not develop resistance to atrazine, mesotrione and topramezone.
CONCLUSIONS This study demonstrated that Trp574Arg substitution was the main reason for crabgrass resistance to ALS-inhibiting herbicides. To our knowledge, this is the first report of Trp574Arg substitution in a weed species, and is the first report of target-site mechanisms of herbicide resistance for crabgrass.