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In the last years public concern about environmental pollution due to pesticides has been growing and, among other consequences, this situation boosted research on physical weed control methods as an alternative to herbicides. Recent researches have been carried out about the feasibility of the use of water steam as a replacement of chemical weeding in particular conditions where no chemical residues are allowed, e.g. in organic farming. Tests carried out with a steam jet directed on the weeds confirmed its effectiveness in killing weeds, but also showed high energy requirements and very low working speed despite the high thermal contents of steam. To improve weed control efficiency, a chamber where the steam can condense on the surfaces of the plants was developed in order to exploit the high efficiency of latent heat transfer of condensing water steam, as suggested by a theoretical analysis. Preliminary lab test confirmed the validity of this approach, showing higher energy efficiency in respect to the direct application. Following these encouraging results a self-propelled machine was equipped with a condensation chamber specifically designed to perform field tests on 5 species (two dicots and three grasses), to be treated at two different growth stages. The dose-response curves obtained after treating the plots with 5 to 6 different travel velocities showed good effectiveness. The dicots were effectively controlled with doses lower than 500 kJ m-2 (corresponding to 2 km/h travel speed), while maize was able to regrow after the treatment, requiring about twice the dose.

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). Innovazioni meccanico-impiantistiche per l'agricoltura, l'agro-industria e l'acquacoltura, 2003, Anacapri, Italy. 3.Bond W., Davies G., Turner R. J.. A rewiew of thermal weed control. 2006 http://www.gardenorganic.org.uk/organicweeds 4.Bond W. & Grundy A. C.. Non-chemical weed control management in organic farming systems. Weed Research 2001, 41, 383-405 5.De Zanche C., Baldoin C., Friso D., Sartorato I., Zanardi W.. Controllo delle infestanti con getto di vapore (in Italian with English summary). Convegno A.I.I.A. 2005 L'ingegneria agraria per lo sviluppo sostenibile dell'area mediterranea, 2005, Catania. 6.Hansson D., Ascard J.. Influence of development stage and time of assessment on hot water weed control. 2002 Weed Research 42, 307-316. 7.Hansson D.. Hot water weed control on hard surface areas. 2002, Acta Universitatis Agriculturae Sueciae 323, 1401-6249 Sveriges Lantbruksuniversitet. Uppsala, Sweden. 8.Sartorato I., Zanin G., Baldoin C., De Zanche C.. Observations on the potential of microwaves for weed control. 2006 Weed Research 46, 1-9 9.Syrvidas A., Lazauskas P., Vasinauskiené R., Kerpauscas P.. Thermal weed control by water steam, 5th EWRS Workshop on Physical Weed Control, 2002, Pisa, Italy, p. 253-262.

The paper focus on relationships between early growth and competitivity of weed species. A seedling is defined as a young plant from its emergence until the end of exponential growth. Factors affecting seedling growth are reviewed and relationships among species characteristics, environmental and agronomic factors are discussed. In most experiments seedling relative growth rate is negatively correlated with seed weight, its main determinant being specific leaf area. The first results of experiments conducted by the authors show that seedling weight at the end of exponential growth appears to be related to parameter I of Cousens' hyperbola. The relative size of the plants when competition starts, determined by the relative time of plant emergence, initial seedling weight and relative growth rates, is concluded to be of paramount importance in defining plant competitive ability. The paper emphasises that further insight into the mechanisms which drive early plant growth could enhance our predictive ability. The study of simple attributes of seeds and seedlings that could be used to predict their adult plant behaviour and the grouping of weed species in 'functional groups' with homogeneous competitive traits is suggested as a way to expand applicability and predictability of decision-making programmes.

In cella climatica si sono studiate le risposte morfo-fisiologiche indotte da due livelli di radiazione fotosinteticamente attiva (PPFD pari a 100 µmol m-2s-1 e 400 µmol m-2s-1) su due graminacee infestanti, Sorghum halepense (L.) Pers. e Panicum miliaceum (L.), entrambe caratterizzate da ciclo fotosintetico C4. Le due specie hanno manifestato una notevole risposta al fattore luce sia in termini di ritmi di crescita che di assimilazione, sia come risposte adattative a livello di morfologia fogliare e di ripartizione degli assimilati, evidenziando meccanismi adattativi simili. Quando allevate a bassa intensità luminosa hanno manifestato tassi di accrescimento ridotti e stabili nel tempo e rilevanti adattamenti della struttura fogliare (SLA da doppio a quadruplo rispetto alle piante allevate ad alta intensità). Nel primo periodo di crescita sono stati rilevati tassi di accrescimento molto elevati e differenziati fra le tesi; in entrambe le specie le piante cresciute ad alta intensità a 14 giorni dall'emergenza avevano già accumulato più sostanza secca di quella raggiunta a fine ciclo dalle piante allevate a bassa intensità, confermando l'importanza dei primissimi giorni nella determinazione della capacità competitiva. Il S. halepense ad entrambi i livelli luminosi ha evidenziato ritmi di accrescimento più sostenuti rispetto al P. miliaceum, che, nonostante la crescita limitata, ha differenziato gli organi fiorali anche al livello di radiazione inferiore. In generale il comportamento del S. halepense è riconducibile ad una strategia di tipo competitivo, mentre P.miliaceum sembra possedere una strategia prevalentemente ruderale.

Si sono studiati l'accrescimento ed alcune modificazioni fisiologiche indotte da due livelli di radiazione fotosinteticamente attiva (420 e 210 mmol m-2 s-1)su due malerbe (Solanum nigrum L. ed Amaranthus cruentus L.) aventi cicli fotosintetici rispettivamente C3 e C4. Le prove sono state condotte in cella climatica ad una temperatura ed umidità relativa fissate a 27 °C / 40% durante il giorno e 18 °C / 60% durante la notte. Il fotoperiodo era di 15 ore. Il S. nigrum, ad entrambi i livelli luminosi, ha evidenziato una certa superiorità, presentando valori più elevati sia di area fogliare che di sostanza secca durante tutto il periodo considerato (0-47 giorni dall'emergenza). Tale superiorità è probabilmente riconducibile sia ad un maggiore peso unitario dei semi sia alla capacità di sviluppare rapidamente un vasto apparato fogliare. L'A. cruentus è risultato particolarmente penalizzato al livello luminoso inferiore. Le due specie hanno evidenziato diverse strategie di risposta alla disponibilità del fattore luce. Il S. nigrum ha presentato un modello di distribuzione della biomassa abbastanza indipendente dalle condizioni di luce (LWR e RSR non variano molto), concentrando gli adattamenti a livello di struttura fogliare, mentre l'A. cruentus ha operato su entrambi i meccanismi attuando una diversa distribuzione della sostanza secca e modificando la struttura delle foglie e il loro contenuto in pigmenti fotosintetici. La statura delle due malerbe è stata fortemente modificata dal trattamento luminoso, confermando la maggiore potenzialità competitiva del S. nigrum in presenza di bassi livelli luminosi. Dall'analisi dei risultati emerge il ruolo fondamentale dei primi stadi vegetativi nel determinare la competitività di una specie.