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A heated, plant-based foam has been shown to kill weeds as effectively as a commercial chemical spray and may be a safer, eco-friendlier alternative.

鈥淚t鈥檚 really fascinating, it works very well regardless of the weed growth stage,鈥� says at the Agricultural University of Athens, who conducted an independent study of the hot foam at two small olive groves in Greece.

Farmers remove weeds because they steal water and nutrients from food crops and can attract destructive insects and pathogens.

The most common way to get rid of weeds is to spray them with chemical herbicides like glyphosate. But ongoing controversy over whether such products are linked to increased cancer risk in people and harm other animals like frogs has prompted the search for alternatives.

One chemical-free way to kill weeds is by applying heat, which makes the plants shrivel up and die. However, attempts to kill weeds using hot water and steam have had limited success because the heat rapidly escapes to the atmosphere rather than damaging the plants.

To overcome this issue, UK company Weedingtech has developed a foam made of natural oils and sugars from plants like wheat, maize and rapeseed that is able to trap and retain heat when mixed with hot water.

The mixture is applied to weeds at a temperature of 97掳C (207掳F) using a machine with a handheld spraying device. This creates a thermal blanket around the weeds that makes them die within 48 hours. The foam and dead weeds then biodegrade into the soil.

Travlos and his colleagues found that the hot foam worked as well as glyphosate at removing weeds at the two olive groves, reducing total weed biomass by about 96 per cent.

It was also superior to other non-toxic weed removal techniques like mowing, mulching and spraying with a plant-based weedkiller called pelargonic acid.

They determined this by applying the different weed treatments to separate sections of the olive groves, then monitoring the weeds鈥� decline using an optical device and by weighing the remaining biomass.

The hot foam is marginally more expensive than glyphosate and slower to apply, but it is more cost-effective than other non-herbicide options currently available, says , commercial director at Weedingtech.

Several towns and cities, including in the UK and in the US, have also trialled the hot foam for removing weeds from pavements, playgrounds and other urban areas. They have found it to be effective and convenient, especially because its lack of toxicity means it can be applied when other people are around, says Hamilton.

At this stage, the approach is unlikely to be useful for controlling weeds in very large fields of crops because of the energy costs of heating the foam and the time taken to apply it, says at the University of New England in Armidale, Australia.

However, Weedingtech is receiving a large amount of interest from farmers with low-volume, high-value crops such as in vineyards, says Hamilton.

Several other non-herbicide weed control methods are also in development, says at the University of Sydney. These include killing weeds with electricity or lasers, or cutting them down with powerful water jets, he says.

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