Optimisation of hot-water application technology for the control of broad-leaved dock (Rumex obtusifolius)

Abstract

In organic farming, the control of broad-leaved dock (Rumex obtusifolius) via hot-water treatment of the upper root region (hypocotyl) is a new alternative to the current standard control method involving manual digging-out of the roots. This comparative study looks at five different hot-water application techniques. The aim is to optimise the control method in terms of water and energy requirement to obtain a mortality rate of the treated plants of at least 80%. The studied parameters were the application, the amount of water, the water temperature, the soil moisture content and the soil type. In total, 813 plants of varying size were treated (120-225 plants per treatment). The success of each treatment was rated 12 weeks after it was applied. Based on the results, the preferred treatment in terms of water and energy requirement was a commercially available rotary nozzle. With this nozzle, for example, at 40 vol.-% soil moisture, 1.6 L of water at a temperature of 90°C was necessary for successful Rumex control. The rotary nozzle could be used as a non-contact system, and was therefore the most user-friendly of the application techniques examined. IntroductionThroughout Europe, grassland areas managed according to organic-farming principles are increasing. The percentage of organically managed areas in the whole of the EU, for example, rose from 5,913,359 hectare (ha) in 2004 to 7,542,604 ha in 20087,542,604 ha in (Köpke et al., 2011. In Switzerland, the percentage of these areas has remained practically constant over the last nine years and, at 116,188 ha in 2011, accounted for 11% of the total agricultural area (Bundesamt für Statistik BfS, 2012).One of the greatest problems in organically managed grassland is posed by broad-leaved dock, Rumex obtusifolius (Zaller, 2004). Broadleaved docks contain high levels of oxalic acid and oxalates, which can cause health problems in large doses (Brune, 1955;Roth et al., 2012). Avoided by grazing animals on account of the substances it contains, the plant causes reduction in livestock performance when present in conserved feed. Oswald and Haggar (1983) reckoned that a ground cover of 20-30% broad-leaved dock would reduce the vegetation volume of valuable fodder plants up to 20%. To avoid these negative effects, the dock stocking on grassland should be minimal.Differing from other weeds, the physical control of broad-leaved dock is difficult because of the growth and the regenerative power of its taproots. The primary taproot of the dock develops in the first year after germination (Bond and Turner, 2003). In the second year, the plant produces secondary taproots (Pino et al., 1995). Thereafter, the taproot system increases and divides. The clonal growth of one plant can affect large weed-covered areas (Bond and Turner, 2003). The regenerative power of R. obtusifolius lies in the hypocotyl. It is about 0.1 m long and located in the first section of the partially very complex underground organs (Roberts and Hughes, 1939). Stored reserve materials enable the plan...

Controlling Rumex obtusifolius by means of hot water

“…Thermal methods capable of reaching the hypocotyl region are microwaves, infrared technology and steam or hot‐water treatment. The advantages and disadvantages of individual treatments have already been discussed by the authors in a previous article (Latsch & Sauter, ).…”

“…One of the main problems in managing environmentally driven grassland farms is infestation with broad‐leaved dock species (Latsch & Sauter, ). On lowland sites, these are mainly Rumex obtusifolius L. (broad‐leaved dock) and Rumex crispus L. (curled dock); in the highlands, Rumex alpinus L. (alpine dock) is present, as well (Zaller, ).…”

“…The application method for this procedure was then refined in order to optimise the energy and time required. Five different hot‐water application heads were investigated (Latsch & Sauter, ), the most efficient application system being a rotating nozzle (Kärcher ‘Dirt Blaster’ model, Type: 4.763–253.0, Kärcher, Winnenden, Germany) which allowed contact‐free treatment of the root region. According to the construction, the nozzle creates a rotating pencil jet, which combines the high water pressure of a pencil jet with the extensive treatment of a fan jet.…”

Weekly defoliation controls, but does not kill broad‐leaved dock (Rumex obtusifolius)

“…Although this procedure presents a high success rate of 90% (Roy Latsch, Agroscope, unpublished data), it is very labour‐intensive. Effective methods aimed at damaging or removing the taproot include microwaves (Latsch et al ., ), chopping (Van Evert et al ., ), treatment with a hot steel rod (Bond et al ., ) and the application of hot water to the roots (Latsch & Sauter, ; Latsch et al ., ). Mowing or cutting can be used to control Rumex (Courtney, ; Stilmant et al ., ).…”

“…This is effective but prone to mechanical failure in dry or stony soil. In the DockWeeder project, the hot water method of controlling Rumex (Latsch & Sauter, ; Latsch et al ., ) was automated (http://dockweeder.eu/ and http://ict-agri.eu/node/35755). Both methods target the taproot and consume a large amount of energy; the hot water robot additionally needs to transport a large amount of water.…”