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Woodchip mulch could protect from scab

Evidence that the severity of apple scab is reduced by using willow woodchip mulches could be put to the test in commercial orchards later this year as part of the Innovative Farmers Field Labs programme. A meeting being planned for this autumn will present results from small-scale research undertaken so far by Dr Glynn Percival, plant physiologist at the Bartlett Tree Research Laboratory at Reading University, and will be an opportunity for interested growers to collaborate in planning trials in their own orchards.

“Willow is rich in salicylic acid, a compound known to induce disease resistance responses when applied to many plant species,” said Dr Percival. “It is expensive to use in its pure form, so over the last two years we have run trials on our site at Reading University using the old apple variety Crown Gold, which is very susceptible to scab. We found that, although it didn’t eliminate scab, it does result in a significant reduction of around 40-60% in severity, which we believe is down to the salicylic acid from the willow chips getting into the soil and being absorbed by the apple tree roots.”

Dr Percival works mainly in the amenity tree sector, so is looking to use the Innovative Farmers programme to collaborate with growers to extend the research to commercial varieties in orchards in various areas of the country. AHDB Horticulture will also be supporting the trials. “One thing we’d like to find out is whether the mulch treatment can reduce the number of fungicides that growers need to use,” he said. “We also want to know how long a single application of mulch lasts; we think it will only need to be applied every second or third year. And, as the salicylic acid induces a very general resistance response, mulches may also help to protect against other diseases or pests.”

Meanwhile, trials continuing at Reading include a comparison of willow species to see if there are differences in salicylic acid content or disease suppression; and to use the mulches in combination with other treatments, including biochar.

The ‘field labs’ programme is run by the Soil Association and funded through the Prince’s Trust using profits from the Duchy brand of organic products. For more information visit www.innovativefarmers.org where details of the autumn meeting will be published.