Willow woodchip for top fruit scab control

Investigating the efficacy of willow woodchip mulch as a control for apple scab.

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Field Lab Timeline

    6/30/2018 11:00:00 PM
  • Idea formation

    Idea formation
  • 7/11/2018 11:00:00 PM
  • Method discussion and finalisation

    Method discussion and finalisation
  • 9/10/2018 11:00:00 PM
  • Funding application for Phase 1 - salicylic acid analysis

    Funding application for Phase 1 - salicylic acid analysis
  • 11/1/2018 12:00:00 AM
  • Salicylic acid content analysis

    Salicylic acid content analysis
  • 1/30/2019 12:00:00 AM
  • Phase Two funding application

    Phase Two funding application
  • 2/21/2019 12:00:00 AM
  • Phase Two meeting

    Phase Two meeting
  • 3/31/2019 12:00:00 AM
  • Application of treatments

    Application of treatments
  • 9/29/2019 11:00:00 PM
  • Collection of leaf and fruit samples

    Scab % assessed Leaf samples collected for N and Ca content Fruit analysed for sugar content

    Collection of leaf and fruit samples
  • 12/31/2019 12:00:00 AM
  • Analysis of samples

    Analysis of samples
  • 1/31/2020 12:00:00 AM
  • Technical reports

    Technical reports
For further information hover over the above milestone marks
  • Discussion

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  • Achievements

    November 2019

    Our findings from the field lab

    Results showed that when data from all trial sites is pooled there was no statistically significant influence of willow wood chip on leaf and fruit apple scab severity. However, applying willow wood chip did significantly reduce scab severity on some orchards/trial sites.

    Results consistently showed a ‘trend’ across all trial sites towards lower leaf and fruit scab severity and higher leaf nutrient content following application of a willow mulch around the base of fruit trees. Trial sites were treated with mulches made from primarily white willow species (S.alba, S.alba ‘Chermasina, S.fragalis), which a later analysis was shown to be the lowest SA containing willow species. This does raise the possibility that treating with a different willow species i.e. S. daphnoides or S. matsudana tortuosa with an inherently higher SA content would result in even lower scab severity and higher leaf nutrient content. In support of this S.daphnoides was used at the Aston Manor site where significantly lower scab levels were recorded.

    At some of the sites visited the amount of willow mulch applied was far lower than that recommended (5kg per tree) while the size of the tree was quite large (4-6 metres). This raises the possibility that the overall amount of SA provided to the tree was insufficient to induce any resistance response.

    Further research has identified that SA is primarily concentrated within willow bark. Consequently the use of a willow bark mulch (a by-product of basket weaving) would be superior to that of a mulch made from willow wood and offers possibilities for future research.

    To download the final report you must be a member of the Innovative Farmers network. Join now to access the report and other materials developed as part of this field lab from the top right of this page.

    Milestone: Technical reports

    August 2019

    Monitoring for apple scab

    The group will be assessing and monitoring levels of apple scab in mid August, in both the treated and untreated trees using the leaf and fruit scab severity scale available on the documents tab of this page. Researcher Glynn Percival will be analysing the results from the participating orchards, check back here for updates or sign up to the Innovative Farmers newsletter to hear when results are available.

    (Use your free Innovative Farmers log in to access the documents on the top right of this page. If you have any problems accessing the website call 0117 9874572 or email ehurrell@innovativefarmers.org).

    Milestone: Collection of leaf and fruit samples

    February 2019

    Grower meeting

    The group met at one of the trial locations and discussed and agreed the final methodology, with input from researcher Dr Glynn Percival of Bartlett Tree Laboratory. Group coordinator Tony Little sourced willow woodchip which was dispersed amongst the triallists, and Glynn gave a demonstration of the optimum mulching technique, particularly the optimum dimensions and depth to lay the woodchip in order for the salicylic acid content of the woodchip to take effect.

    Grower protocols are detailed in Field Lab documents on the top right of this page - log in for free to view. You can also view the presentation from Dr Glynn Percival on the research that has been done in the area of willow woodchip as a treatment.

    In brief, the mulching guidelines are:
    Select your 'control' trees and your 'treated' trees, with at least two guard trees between them.
    Add around 5kg woodchip mulch to the area under the crown of the selected 'treated' trees, up to 1 meter around the trunk. Leave a few inches of the base of the trunk free of mulch to allow air flow around the root collar. Lay the mulch between 5-10cm deep, but no deeper than 10cm. There is no need to compost the woodchip, as it is found to be effective when fresh.
    Apply the mulch in January/February, with the salicylic acid taking around 4-6 weeks to leach in the soil and affect the trees, this should coincide with the tree coming in to bud. If application is left too late scab will already have the chance to take hold.

    A range of growers are taking part in this trial, including organic and conventional orchards, and several members of the National Association of Cider Makers along with smaller scale independent producers.

    Milestone: Method discussion and finalisation

    January 2019

    Phase Two funding granted

    Funding for phase two of this field lab has been granted, and the group will meet on February 21st at one of the members orchards to see a demonstration and finalise their application methodology. The results from phase one (analysis of salicylic acid levels in the ten most common willow species) will inform each growers choice about which species of willow to use, along with consideration of cost and availability.

    Milestone: Phase Two funding application

    December 2018

    Results of SA content in Willow species

    Phase One results - a diagnostic review of the Salicylic Acid content in willow species

    Samples of the ten mostly commonly used willow species were collected at the Royal Botanic Gardens, Kew, and analysed at the Bartlett Tree Research Laboratory at the University of Reading. The diagnostic report gives the salicylic acid content of the tissue samples, showing significant differences in salicylic acid content across the ten different species.

    Salicylic Acid (mg/g FW)
    S. caprea 1.95
    S. alba 0.20
    S. daphnoides 3.21
    S. alba ‘Chermesina’ 1.62
    S. erythrotoflexuosa 0.38
    S. fragilis 1.65
    S. triandra 0.60
    S. viminalis 0.21
    S. matsudana tortuosa 2.33
    S. pentandra 0.81

    These results will be used by growers to inform their choice of willow species they will use as a woodchip mulch during the field lab.

    Next steps
    Field lab members will be meeting in late January to discuss in detail the application of treatments and gathering field data to ensure consistency across the sites. Applications will then be carried out at each site on a selection of ten trees, at a time most suitable time for each producer (eg. cider producers will apply after harvest Jan-Feb), with a further selection of trees used as controls.

    Milestone: Salicylic acid content analysis

    October 2018

    Methods meeting

    The trial will compare the incidence of scab in those trees receiving willow woodchip mulch treatment, and the controls, using a simple design:

    Phase One
    - Analyse the Salicylic Acid content of the ten most commonly available willow species

    Phase Two
    - Each of the ten growers will use a single species woodchip mulch, selecting a willow species based on Phase One results and availability
    - 10 trees per treatment with 10 trees as controls, using trees at the edge of rows that are marked with signs
    - Applications will take place in dormant season in January/February after harvest and clearing
    - Incidence of scab will be measured once in mid-summer

    Further iterations of the trial in Year 2 may include variables such as application timing, comparing different species of willow within a site, and the use of biochar to increase the efficacy of the salicylic acid.

    Milestone: Method discussion and finalisation

    July 2018

    Initial project meeting

    A group of growers interested in exploring alternatives to copper as a solution to scab will run a field lab to assess the efficacy of willow woodchip mulch as a scab prevention treatment. Willow has relatively high levels of Salicylic Acid and indications suggest a single application of woodchip mulch in early spring can help manage apple scab later in the season. The mechanism is thought to be analogous to vaccination in animals.

    Phase One of this project will be to analyse the Salicylic Acid content of the ten most commonly available species of willow.

    Milestone: Idea formation

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