Table 2 Parameters of the log–logistic equations^a used to calculate the concentration (µM) of the ALS-inhibiting herbicides needed to inhibit the ALS activity by 50% (I₅₀) in two biotypes (S, susceptible; R, resistant) of E. heterophylla.

Herbicide^b	Biotype	c	d	b	R²aj	P value	I₅₀	RF
Bensulfuron (SU)	S^†	—	100.0 ± 5.1	2.05 ± 0.11	0.99	<0.0001	1.5 ± 0.1	12.5
Bensulfuron (SU)	R	7.1 ± 0.3	100.8 ± 7.3	1.36 ± 0.08	0.99	<0.0001	19.1 ± 0.7	12.5
Bispyribac (PTB)	S	10.4 ± 0.5	101.0 ± 3.1	0.99 ± 0.05	0.98	<0.0001	137.7 ± 6.7	2.0
Bispyribac (PTB)	R	21.9 ± 1.1	100.1 ± 4.9	2.31 ± 0.10	0.99	<0.0001	269.3 ± 6.4	2.0
Florasulam (TP)	S^†	—	101.5 ± 3.9	1.18 ± 0.04	0.99	<0.0001	1.3 ± 0.1	524.7
Florasulam (TP)	R	16.9 ± 0.7	100.8 ± 1.2	0.93 ± 0.04	0.98	<0.0001	692.6 ± 11.1	524.7
Flucarbazone (SCT)	S	3.9 ± 0.2	100.2 ± 6.8	0.80 ± 0.02	0.99	<0.0001	20.7 ± 1.0	17.3
Flucarbazone (SCT)	R	12.5 ± 0.6	100.2 ± 2.6	1.28 ± 0.04	0.99	<0.0001	358.3 ± 9.5	17.3
Imazamox (IMI)	S	1.8 ± 0.1	100.0 ± 1.9	0.56 ± 0.03	0.98	<0.0001	33.7 ± 1.0	16.0
Imazamox (IMI)	R	19.6 ± 1.0	100.2 ± 3.1	0.17 ± 0.01	0.99	<0.0001	538.4 ± 8.1	16.0

^aY = c + {(d − c)/[1 + (x/g)^b]} (four parameters) where: c and d are the coefficient corresponding to the lower and upper asymptotes, respectively; b is the slope of the line, x the herbicide concentration, and g is the herbicide concentration at the inflection point, hence the I₅₀. ^†Regression analyses adjusted to a model of three-parameters (Y = d/1 + (x/g)) assuming that the lower limit is zero. ^bALS chemical classes: sulfonylureas (SU), imidazolinones (IMI), triazolopyrimidines (TP), pyrimidinylthiobenzoates (PTB) and sulfonylamino-carbonyl-triazolinones (SCT). ±Standard error of the mean (n = 5). R²aj = 1 − (sums of squares of the regression/corrected total sums of squares). P value = significance level of the nonlinear model. RF = Resistance factor = I₅₀R/I₅₀S.

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