Image analysis as a non-destructive method to assess regrowth of weeds after repeated flame weeding

Figures & data

Table I. Treatment plan from May to October 2008.

		1	2	3	4	5	6	7	8	9	10
Mean dose (kg ha^−1)	Number of treatments	Week 20	Week 22	Week 24	Week 26	Week 28	Week 30	Week 32	Week 34	Week 36	Week 38
20	10	1	1	1	1	1	1	1	1	1	1
40	10	1	1	1	1	1	1	1	1	1	1
80	10	1	1	1	1	1	1	1	1	1	1
100	10	1	1	1	1	1	1	1	1	1	1
120	10	1	1	1	1	1	1	1	1	1	1
180	10	1	1	1	1	1	1	1	1	1	1
20	8	1	1	1	1	1	1	0	1	0	1
40	8	1	1	1	1	1	1	0	1	0	1
80	8	1	1	1	1	1	1	0	1	0	1
100	8	1	1	1	1	1	1	0	1	0	1
120	8	1	1	1	1	1	1	0	1	0	1
180	8	1	1	1	1	1	1	0	1	0	1
20	6	1	1	0	1	0	1	0	1	0	1
40	6	1	1	0	1	0	1	0	1	0	1
80	6	1	1	0	1	0	1	0	1	0	1
100	6	1	1	0	1	0	1	0	1	0	1
120	6	1	1	0	1	0	1	0	1	0	1
180	6	1	1	0	1	0	1	0	1	0	1
20	4	1	0	0	1	0	0	1	0	0	1
40	4	1	0	0	1	0	0	1	0	0	1
80	4	1	0	0	1	0	0	1	0	0	1
100	4	1	0	0	1	0	0	1	0	0	1
120	4	1	0	0	1	0	0	1	0	0	1
180	4	1	0	0	1	0	0	1	0	0	1
20	2	1	0	0	0	0	1	0	0	0	0
40	2	1	0	0	0	0	1	0	0	0	0
80	2	1	0	0	0	0	1	0	0	0	0
100	2	1	0	0	0	0	1	0	0	0	0
120	2	1	0	0	0	0	1	0	0	0	0
180	2	1	0	0	0	0	1	0	0	0	0
Note: The doses are mean planned dose of propane. Tree repetitions were carried out for each combination of dose propane and treatment interval.

Figure 1.  Response of Lolium perenne as a function of propane dose (kg ha⁻¹) and number of flamings per year. (A) Response was measured as plant dry weight, (B) percentage green cover estimated by image analysis and (C) percentage green cover estimated by visual assessment on images. Each bar corresponds to the mean of nine replicates (three per block, 18 replicates for control plants (six per block).

Table II. Equation parameters (model 2) and standard errors (SE) of the effect of flame treatment on perennial ryegrass after different number of treatments per year.

		Slope at ED50
Treatments number per year	Assessment method	b (SE)	ED50 (SE) (kWh ha^−1)	ED80 (SE) (kWh ha^−1)	ED90 (SE) (kWh ha^−1)
4	Relative plant dry weight	1.01 (0.092)	216 (14.9)	866 (100.1)*	1952 (361.7)*
	Relative plant cover (image analysis)	1.56 (0.119)	173 (8.3)	421 (30.0)	707 (73.8)
	Relative plant cover (visual assessment)	1.45 (0.130)	114 (7.5)	298 (21.7)	521 (58.8)
6	Relative plant dry weight	1.39 (0.122)	128 (10.4)	348 (22.5)	623 (62.2)
	Relative plant cover (image analysis)	1.10 (0.089)	252 (15.2)	885 (80.2)	1846 (263.7)*
	Relative plant cover (visual assessment)	0.92 (0.093)	147 (14.9)	663 (67.9)	1598 (287.1)*
8	Relative plant dry weight	1.42 (0.141)	110 (11.4)	292 (19.0)	517 (49.5)
	Relative plant cover (image analysis)	1.57 (0.099)	304 ( 13.6)	736 (38.1)	1236 (95.3)
	Relative plant cover (visual assessment)	1.25 (0.94)	189 (13.2)	571 (35.6)	1091 (107.5)
10	Relative plant dry weight	1.76 (0.136)	144 (9.2)	316 (14.4)	501 (33.0)
	Relative plant cover (image analysis)	2.04 (0.101)	334 (10.3)	659 (22.0)	981 (46.7)
	Relative plant cover (visual assessment)	1.92 (0.112)	203 (8.4)	418 (16.4)	637 (35.3)
Note: The effect of the treatments was assessed by three different methods (1) Biomass samples (relative dry weight), (2) percentage green cover assessed by image analysis or (3) percentage green cover assessed by visual assessment. Dose was calculated as total dose in kg propane ha^−1 after 4, 6, 8 or 10 treatments.
*Outside observed dose range.

Figure 2.  Dose–response curves for the total propane dose effect on relative plant dry weight or plant cover after flaming of perennial ryegrass with different number of treatments per year. (A) 4 Treatments per year, (B) 6 treatments per year, (C) 8 treatments per year and (D) 10 treatments per year. Each data point corresponds to the mean of nine samples. The upper asymptote (control plants) is based on the mean from 18 samples. Parameter estimates are given in Table I. The total dose requirement was assessed by three different methods: Plant dry weight (DW), weed cover assessed by image analysis (IA) or visual assessment (VA).