Efficacy of heat for weed control varies with heat source, tractor speed, weed species and size

Figures & data

Figure 1. Prototype direct-fired steam weeder (Merfield et al. 2009). Parts: (1) Ecoflam burner, (2) combustion chamber, (3) water injection duct, (4) water pump, (5) steam distribution duct, (6) hood, (7) front and rear skids, (8) chimney, (9) tool frame, (10) water tank, (11) diesel tank. The electrical generator is not visible as it is on the far side of the water tank.

Figure 2. Schematic diagram of the direct-fired steam weeder boiler and steam application system (Merfield et al. 2009). Top, plan view of direct-fired steam boiler; bottom, side view of steam distribution duct and hood, aligned with the plan view. Parts: numbering is consistent with Figure 1, (1) Ecoflam burner, (2) combustion chamber with ceramic wool insulation, (3) water injection duct, (5) steam distribution duct, (6) hood, (8) chimney, (12) flame from burner, (13) water nozzle and water spray, (14) slot in bottom of steam distribution duct, (15) flaps, (16) soil surface and weed seedlings. Arrows indicate direction of hot gas and steam mixture. Steam is created by the hot gasses produced by the burner (1 and 12) vaporising the fine spray of water from the water nozzle (13), which are then carried by the flow of gas from the burner to the steam distribution duct (5, both diagrams), through the slot in the bottom of the duct (14) to the underneath of the hood (6) where it heats the weeds, before exiting via the chimney (8). Flaps (15) at the front and rear are to reduce the amount of wind blowing under the hood and increase steam retention.

Figure 3. The Lincoln University flame weeder (de Rooy 1992).

Table 1. The effect of steam and flame weeding at five tractor speeds on the survival of mustard plants between cotyledon and two true leaf stage (expressed as a proportion of the control) (Experiment 1).

Weeder	Tractor speed (km h^−1)
	3	4	5	6	7	Mean
Flame	8	71	96	99	99	75
Steam	0	7	48	66	78	40

Notes: Least Significant Difference (weeder type; P < .05) = 12.1. Least Significant Difference (tractor speed; P < .05) = 19.2. Least Significant Difference (interaction; P < .05) = 27.2.

Table 2. Effect of flame and steam weeding at 3 km h⁻¹, at different growth stages on plant survival (Experiment 2).

Species	Growth stage (and height)	Steam	Flame	Significance	LSD P < .05
Amaranthus retroflexus	Cotyledons	0	0
	Two true leaves (20 mm)	0	0
	Four true leaves (70 mm)	52	60	ns
	Six true leaves (80 mm)	96	84	*	11.9
Chenopodium album	Cotyledons	0	0
	Two true leaves (10 mm)	0	0
	Four true leaves (60 mm)	28	16	ns
	Eight true leaves (100 mm)	80	72	ns
Capsella bursa-pastoris	Cotyledons	0	0
	Two true leaves (10 mm)	4	0
	Four true leaves (10 mm)	28	32	ns
	Six true leaves(30 mm)	84	84	ns
Daucus carota	Cotyledons	0	0
	One true leaf (10 mm)	0	0
	Two true leaves (20 mm)	12	0
	Four true leaves (40 mm)	52	56	ns
Fumaria officinalis	Cotyledons	0	0
	Two true leaves (10 mm)	4	12	ns
	Four true leaves (15 mm)	56	56	ns
	Six true leaves (30 mm)	100	92	ns
Lolium perenne	Cotyledon	100	100
	Two true leaves (1 cm)	84	100
	Four true leaves (6 cm)	100	100
	Eight true leaves (10 cm)	100	100
Polygonum aviculare	Cotyledons	0	0
	Two true leaves (20 mm)	0	0
	Four true leaves (60 mm)	0	0
	Eight true leaves (130 mm)	20	28	ns
Rumex crispus	Cotyledons	0	0
	Two true leaves (10 mm)	4	8	ns
	Four true leaves (30 mm)	68	60	ns
	Six true leaves (70 mm)	100	100
Spergula arvensis	Cotyledons	0	0
	Two true leaves (10 mm)	0	0
	Four true leaves (15 mm)	68	44	*	14.3
	Six true leaves (30 mm)	92	76	*	14.3
Stellaria media	Cotyledons	0	0
	Four true leaves (6 cm)	0	0
	Eight true leaves (10 cm)	0	0
	Fourteen true leaves (15 cm)	0	0
Solanum sarrachoides	Cotyledons	0	0
	Two true leaves (15 mm)	0	4
	Four true leaves (60 mm)	72	60
	Six true leaves (80 mm)	88	72	*	15.6
Trifolium repens	Cotyledons	0	0
	Two true leaves (10 mm)	0	0
	Four true leaves (25 mm)	0	4
	Six true leaves (60 mm)	28	40	*	10.4
Veronica agrestis	Cotyledons	0	0
	Two true leaves (1 cm)	0	0
	Four true leaves (1.5 cm)	0	4
	Eight true leaves (11 cm)	0	8

Note: ns = not significant.

*Significant at P < .05.

Merfield CN, Hampton JG, Wratten SD. 2009. A direct-fired steam weeder. Weed Research. 49(6):553–556. doi: 10.1111/j.1365-3180.2009.00733.x

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de Rooy SC. 1992. Improved efficiencies in flame weeding [Unpublished thesis]. Canterbury: Lincoln University. 87 p.

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