SPOTTED SPURGE (Chamaesyce maculata) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: TRYPTOPHAN 574 to LEUCINE
Spotted Spurge (Chamaesyce maculata) is a dicot plant in the euphorbiaceae family. A single amino acid substitution from Tryptophan 574 to Leucine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Spotted Spurge

Chemical Family	Example Herbicide	Resistance Level
Imidazolinones	Imazethapyr	Not Determined
Pyrimidinyl benzoates	Bispyribac-Na	Not Determined
Sulfonylureas	Chlorsulfuron	Resistant > 10 fold
Triazolopyrimidine - Type 1	Chloransulam-methyl	Not Determined
Triazolinones	Flucarbazone-Na	Not Determined

REFERENCES

McCullough, P. E., J. S. McElroy, J. Yu, H. Zhang, T. B. Miller, S. Chen, C. R. Johnston, and M. A. Czarnota. 2016. ALS-resistant spotted spurge (Chamaesyce maculata) confirmed in Georgia. Weed Science 64 : 216 - 222.

Metsulfuron is used for POST control of spotted spurge in many warm-season turfgrasses. A suspected resistant (R) biotype of spotted spurge was collected from turfgrass in Georgia with a history of exclusive metsulfuron use. Research was conducted to evaluate the resistance level of this biotype to metsulfuron, efficacy of other mechanisms of action for control, and the molecular basis for resistance. Compared with a susceptible (S) biotype, the R biotype required >90 and >135 times greater metsulfuron rates to reach 50% injury and reduce biomass 50% from the nontreated, respectively. The R biotype was also resistant to trifloxysulfuron but was injured equivalent to the S biotype from dicamba, glyphosate, and triclopyr. Gene sequencing of the R biotype revealed a Trp₅₇₄ to Leu substitution that has conferred resistance to acetolactate synthase (ALS) inhibitors in previous research. This is the first report of ALS resistance in spotted spurge. More importantly, this is the first report of a herbicide-resistant broadleaf weed from a turfgrass system in the United States..

This case was entered by Patrick Tranel Email: tranel@illinois.edu

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