Cross-resistance to auxinic herbicides in dicamba-resistant Chenopodium album

Figures & data

Figure 1. The reduction in plant shoot dry weight compared with untreated plants of four populations of Chenopodium album (A [dicamba-susceptible] from Waikato maize fields, P [dicamba-susceptible] from Palmerston North, L and M [dicamba-resistant] from Waikato maize fields), at 49 DAT with five different herbicides each at three rates. Vertical bars represent standard error of the mean.

Figure 2. Fitted aminopyralid dose-response curves (on a logarithmic dose scale) for reduction in shoot dry weight for four populations of Chenopodium album (A [dicamba-susceptible] from Waikato maize fields, P [dicamba-susceptible] from Palmerston North, L and M [dicamba-resistant] from Waikato maize fields) in the A, first, and B, second dose-response experiments. Vertical bars represent ± standard error of the mean.

Table 1. Parameters (see footnote) estimated from the non-linear regression analysis of aminopyralid dose-response experiments for Chenopodium album populations at 49 days after treatment as illustrated in Figure 2A–B.

Population	d ± SE	b ± SE	GR50 ± SE	R/S (A) GR50 ratio	R/S (P) GR50 ratio	R^2
First dose-response experiment
A (susceptible)	103.9 ± 1.3	1.0 ± 0.1	47 ± 15	–	–	0.93
P (susceptible)	103.6 ± 1.9	1.0 ± 0.2	55 ± 18	–	–	0.90
L (resistant)	100.1 ± 2.7	1.4 ± 0.2	699 ± 53	14.8	12.7	0.95
M (resistant)	102.7 ± 3.4	1.6 ± 0.2	896 ± 79	19.1	16.3	0.90
Second dose-response experiment
A (susceptible)	102.6 ± 1.6	1.2 ± 0.2	44 ± 10	–	–	0.94
P (susceptible)	103.1 ± 1.8	1.2 ± 0.1	54 ± 16	–	–	0.98
L (resistant)	101.5 ± 2.4	1.2 ± 0.1	317 ± 46	7.2	5.8	0.95
M (resistant)	101.4 ± 1.5	1.4 ± 0.2	543 ± 85	12.3	10.0	0.95

d, the upper limit; b, the slope around the GR₅₀; SE, standard error; GR₅₀, the rate of herbicide (g ae ha⁻¹) required to reduce shoot fresh weight by 50%; R/S GR₅₀, resistant/susceptible GR50 ratio; R², coefficient of determination.

Figure 3. Fitted picloram dose-response curves (on a logarithmic dose scale) for reduction in shoot dry weight for four populations of Chenopodium album (A [dicamba-susceptible] from Waikato maize fields, P [dicamba-susceptible] from Palmerston North, L and M [dicamba-resistant] from Waikato maize fields) in the A, first, and B, second dose-response experiments. Vertical bars represent ± standard error of the mean.

Table 2. Parameters (see footnote) estimated from the non-linear regression analysis of picloram dose-response experiments for Chenopodium album populations at 49 days after treatment as illustrated in Figure 3A–B.

Population	d ± SE	b ± SE	GR50 ± SE	R/S (A) GR50 ratio	R/S (P) GR50 ratio	R^2
First dose-response experiment
A (susceptible)	103.5 ± 2.2	1.0 ± 0.2	94 ± 17	–	–	0.92
P (susceptible)	102.5 ± 2.3	1.2 ± 0.1	199 ± 24	–	–	0.95
L (resistant)	101.6 ± 1.6	0.8 ± 0.1	627 ± 182	6.7	3.1	0.95
M (resistant)	102.3 ± 2.2	1.1 ± 0.2	1609 ± 254	17.1	8.1	0.90
Second dose-response experiment
A (susceptible)	101.9 ± 1.1	0.9 ± 0.1	75 ± 18	–	–	0.98
P (susceptible)	104.2 ± 2.2	1.8 ± 0.2	153 ± 12	–	–	0.96
L (resistant)	100.7 ± 2.7	1.6 ± 0.1	871 ± 54	11.6	5.7	0.98
M (resistant)	101.4 ± 1.8	2.0 ± 0.2	1407 ± 63	18.7	9.2	0.97

d, the upper limit; b, the slope around the GR₅₀; SE, standard error; GR₅₀, the rate of herbicide (g ae ha⁻¹) required to reduce shoot fresh weight by 50%; R/S GR₅₀, resistant/susceptible GR₅₀ ratio; R², coefficient of determination.