Using Steam For Chemical-free Weed Control

Scientists at the James Hutton Institute are developing a machine for killing weeds in polytunnels and fields that will use nothing more harmful than water steam.

The future of weed control is a challenge for farmers and growers as fewer chemicals are being licensed for use. To prepare for that future, the JHI is developing a novel technique for reducing weeds that will be of particular usefulness for the high value soft fruit industry.

At the Fruit for the Future conference at Invergowrie,a JHI research team explained the processed of developing a new weed killer. They initially considered using flames to kill unwanted plants but deemed the fire risk too large. They also investigated using electrical pulses, which they agreed has potential but the technology isn’t advanced enough at present. Manual cultivators were ruled out as the tynes can strike fruit bushes and damage them. Finally researchers set out to develop a machine which will kill plants with steam.

Agronomist and agritech specialist at JHI, Andrew Christie, said: “Hot water and steam is a mature technology and available in other sectors. It is currently mainly used by councils for municipal or amenity applications but needs refining for plantations.”

The steam generator which Mr Christie is developing will be a modular design and will be able to fit on to tractors and other machines. The current prototype uses a diesel burner to jet out steam at 98 degrees Celsius and above. They are refining the machine so it better retains heat within the hood of the applicator to ensure the steam gets to the right area. When the steam hits the plant it denatures the proteins in the cells killing it. But all the plant needs to be steamed or it will re-grown from the unaffected part.

Initial tests show that the steam is able to kill all the weeds. The main to targets are thistles and groundsel in raspberry and blackcurrant fields. There are now trials planned to try the steamer on a 20 hectare field.

Mr Christie is aiming to have a working prototype by November this year, before developing something ‘close to being marketable’ within two to three years. The current estimate is the machine would cost between £10,000 to £15,000. The project has been supported by the Mains of Loriston trust and PWC pressure washer services.

Also speaking at the conference was Dr Susan McCallum, who explained the direction of plant breeding for the future at JHI. She said there will be increasing focus on climate change adaptability, as plants were 'waking up' sooner in the spring and then getting more affected by late spring frosts. There is also a significant issued with powdery mildew in strawberries which must be tackled.

Part of the JHI's research is looking back at original plants and species of strawberries, raspberries and currants to find resistant traits which can be bred into commercial varieties.

Read more: Controlling grass weeds with reduced tillage systems

The cost of farming crisis has also had an effect on the sector, with prices rising on the shelves. However, worryingly, Dr McCallum explained that when prices rose there was a tendency for shoppers to cut back on purchases. Foreign producers were increasingly marketing product in the UK at a cheaper price due to lower wages in other countries. Figures shared on the day stated that currently around 30% of blueberries, 70% of strawberries and between 50 to 60% of raspberries consumed in the UK are grown here.

There was also excitement from speakers on the future of the UK blueberry sector, as the northern varieties which are grown here have a longer shelf life and can last up to six weeks at a deep chill. This opens the opportunity for exports with huge markets around the world, particularly China which imports very large volumes of the fruit.