Improvement of weed control using steam: laboratory tests on a condensation chamber

IMPROVEMENT OF WEED CONTROL USING STEAM: LABORATORY TESTS ON A CONDENSATION CHAMBER Baldoin C.1*, Sartorato I.2, Bondesan D.1, De Zanche C.1, Friso D.1 1Dept. of Land and Agro-Forestry Systems - University of Padua - Agripolis, viale dell'Università, 16 - 35020 Legnaro Italy; e-mail: cristiano.baldoin@unipd.it 2 Institute of Agro-environmental and Forest Biology, National Research Council - Agripolis, viale dell'Università, 16 - 35020 Legnaro, Italy Introduction In recent years Agro-Environmental Policy in European Union has among its goals the reduction of environmental impact of agriculture, with particular attention to surface and ground waters and air pollution, the protection of biodiversity and the care of the rural landscape. In this context physical weeding methods appear to be worth being considered in the framework of integrated plant protection practices. Current thermal weed control methods use a variety of energy sources in order to generate the heat needed to kill weed seedlings and weed seeds [3]. Different approaches have been considered testing flaming [1], hot water [6], and microwaves [8], to perform post emergence weed control. Thermal weed control by high temperature water steam is a promising technology [9] because it is chemical-free. This factor is a major issue in organic farming systems, where chemical weeding is not permitted [4]. Furthermore physical weed management is acquiring growing importance in urban areas [7]. With the aim of improving effectiveness of water steam in post emergence weeding, a set of laboratory tests was built up, treating young plants of Sudangrass, White Mustard, Velvetleaf, Foxtail and Maize with an experimental equipment fitted with a condensation chamber. Materials and methods Preliminary test on monocotyledons Sudangrass (Sorghum bicolor Pers.), Foxtail (Setaria italica (L.) Beauv.) and Maize (Zea mays L.) and dicots White Mustard (Sinapis alba L.) and Velvetleaf (Abutilon theophrasti Medicus), were carried out on seedlings seeded at two subsequent times differing seven days each other. Tests were carried out using a steam generator (delivering 153 kg h-1 of water steam at low speed and at a pressure near 101,3 kPa) connected to a condensation chamber (0.78L x 0.52D x 0.50H m); it was built using insulating panels of polystyrene assembled on a bearing frame, as an attempt to prevent heat losses. Pots with target plants of about 6 (I stage) and 13 days (II stage) were placed on a belt conveyor and steamed for 0.9 and 3.8 seconds. Percentage of biomass reduction in comparison to an untreated check was assessed 8 days after treatment. An ongoing dose-response experiment is based on a similar approach, using seedlings of S. bicolor, Panicum miliaceum L. (Proso Millet), S. alba and A. theophrasti, at two stages and considering six treatment times, from 0.3 to 9.6 s. Results The first results appear to be encouraging; the screening test showed a biomass reduction from 47 to 100% (Figure 1). With a treatment time of 3.8 s the efficacy was about 100%, irrespective of plant species and stage. Treatment time of 0.9 s resulted in a biomass reduction of about 90% in Mustard and Velvetleaf treated at the second stage; almost full control was achieved on smaller plants. Efficacy on monocots was lower and the effect of plant stage was different in different species; anyway it seems that a trend toward lower level of control in younger plants exists. Foxtail, Sudangrass and Maize showed a biomass decrease of 89, 53 and 47% in younger plants, respectively, while efficacy level in older plants ranged from 62 to 80%. As found in previous researches, monocots seem to be less sensitive to heat shock than dicots. In particular, 8 days after steaming monocotyledons showed an appreciable growing reprise, probably due to the unexposed position of their meristems. Comparing with previous data from this and others research groups [2, 5, 9], weeding effectiveness seems to be enhanced by the presence of a condensation chamber. If these preliminary observations will be confirmed by the ongoing dose-response experiment a more effective field device for physical weed control by water steam could be developed. Figure 1 - Effects of steaming on plants at different developmental stages: a = age 6 days, b = age 13 days References 1.Ascard J.. Effects of flame weeding on weed species at different developmental stages. Weed Research 1995, 35, 397-411. 2.Baldoin C., De Zanche C., Friso D., Zanardi W.. Prime acquisizioni sull'utilizzo del vapore nella lotta alle malerbe (in Italian with English summary). 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