The main advantage of flame weeding lies in that no harmful waste is left on the ground; in fact, LPG burns forming water vapour and carbon dioxide only. The working principle of flame weeding is that this technique produces an intense heat that ‘boils’ weeds.
The carefully directed and controlled flame briefly passes over the weeds without charring them.
Brief exposure to intense heat causes the cell sap to expand and that in turn, disrupts cell walls and interrupts the intracellular feed flow. Nutrients do not reach the cell; within a day or two weeds wilt and die due to continuous evaporation caused by seared cuticles.
Flame weeding does not actually burn weeds, but rather after being treated using heat, flamed weeds undergo a change in pigmentation and the foliage green colour is highly enhanced. This is quite evident a couple of minutes after this method is applied as sap comes out of the cell.
The successful result of this method can be clearly seen some days after application as plants show leaf yellowing common of wilting. It is essential to know proper application times so that the heat applied reaches the correct temperature inside the plant thus reaching all cells and the final result is 100% effective.
If this method is used on plants at their early growth stage (20-25 days after emergence), it will only be necessary to apply heat at 90 – 95 °C for just one second in order to kill these seedlings.
Apply heat at 101 °C for one second on plants at other, more advanced growth stages.
So, in practice it is necessary to apply surplus heat and to vary exposure time to heat of the plants to be flamed. In brief, we can assume a flaming time over the ‘second’ in order to safely use a temperature above 100 °C on all plants.
As consequence of cell explosion after absorbing heat, weeds change colour abruptly to a darker shade. This shows the operator which application speed is adequate for the plants and that weeds have been properly flamed. In turn, this helps to optimise results regarding production and fuel consumption.
Ecologically speaking, flame weeding has an almost negligible impact on the environment.
As LPG burns to form water vapour and carbon dioxide, the flame used is transparent and releases almost no fumes. Therefore, any kind of non-burning pavement or coating can be flame-treated without colour altering
Heating is achieved by quickly passing torches over the layers underneath the surface. In general the temperature applied does not go over 50-60 °C, values that are easily found at the hottest hours in summer.
Therefore, damage caused on microflora and micro-organisms on the soil is minimal; there are no risks for operators and no toxic elements are released into the atmosphere.
As regards environmental health, slow application of flame weeding brings about a further advantage. When the surface of soil, pavement or concrete floor is flame treated at a slow speed, it reaches slightly high temperatures (80 – 90 °C).Therefore, it is well sterilised as there are not any pathogenic germs left.
By choosing this technology, costs are easy to estimate as this flame weeding technique does not pollute the environment, there are no extra after-treatment costs or disposal of toxic waste.
Gas consumption is directly linked to the type of equipment used and the height of weeds to be flame-treated. The most favourable condition to use flame weeding is on weeds at their early growth stages (1-10 cm height).
This is when the best results are achieved at full work speed, and as a consequence gas consumption is reduced when the same area is treated. Hand-held, portable flamers are very versatile. They are also easy to use, yet they entail higher consumption costs compared with equipment mounted on or pulled by a tractor.
Operating costs for tractor-powered flamers are minimised by the fact that they are insulated to contain heat, the main element in flame weeding. It is worth noticing that hand-held, portable flamers are generally used for small areas or where versatility in use and a compact structure are key factors.