Flooding the soil or covering it with plastic film encourages anaerobic bacteria, which produce volatile fatty acids that are lethal to most nematodes, said Wageningen soil expert Leendert Molendijk. But he added: "It does sometimes take a while."
His project team looked at incorporating grass and other organic substances to promote the process, then at feeding the bacteria with plant-based proteins derived from waste. "Soil that has been treated with this product and covered with plastic film is sometimes free from nematodes within two-to-three weeks and more were killed than where it was absent," said Molendijk.
As well as avoiding the use of chemicals such as methyl bromide or Monam, the method does not sterilise the soil as with steaming, he explained. "Certain beneficial soil organisms survive and are able to restore the balance in the soil once the film is removed."
He conceded: "Covering soil with a layer of film is time-consuming, tricky and relatively expensive, and the longer you leave it under the plastic, the greater the risk of damage to it, so undoing the beneficial effect." His team are now testing an alternative covering based on starch. A third of all Dutch agricultural and horticulture land is thought to be infested with nematodes.