The industry-commissioned research by bacterial diseases expert Jan van der Wolf and colleagues at Wageningen UR used a field air sampler to collect airborne bacteria for culturing. It showed that bacteria spread for several metres at most via large drops, but as soon as the bacteria enter the air via minuscule water particles, they can easily be taken up by the wind, said Van der Wolf. "This occurs especially in wet crops that are being mowed."
In such cases, bacteria can end up as far as 100m away from the outbreak source, he said. "At that distance we only found the odd bacterium, but greenhouse tests have taught us that it only requires a few bacteria to infect a plant. This means that there is a real risk of spreading when a healthy crop is situated less than 100m from an infected crop."
His recommendations were: "Mow in dry weather and take the wind direction into account. Place a hood over the mower to prevent spreading and consider disinfecting the machine during or after every mowing session."
Claudia den Braver, policy officer at Dutch plant breeding and propagation sector body Plantum, a co-funder of the research, said: "We will make sure that this new knowledge finds its way to the sector, for example by including the recommendations in the Aardbei Elite quality system, which is used by 95 per cent of the sector in the Netherlands."
Van der Wolf added: "In principle this research can be performed for any crop, for example potatoes, in which large amounts of bacteria are released when the leaves are being destroyed."