Hot water seed treatment to reduce leaf spot

This Riverford sponsored field lab is investigating hot water treatment of crop seeds to help improve yields and reduce waste. The Organic Research Centre's Dominic Amos is helping farmers to develop methods.

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Field Lab Timeline

    9/12/2017 11:00:00 PM
  • Idea formation

    Idea formation
  • 11/24/2017 12:00:00 AM
  • Initial meeting

    Initial meeting
  • 1/31/2018 12:00:00 AM
  • Methods planning

    Methods planning
  • 2/12/2018 12:00:00 AM
  • Methods finalised

    Methods finalised
  • 2/19/2018 12:00:00 AM
  • Proposal submitted

    Proposal submitted
  • 3/5/2018 12:00:00 AM
  • Trial starts

    Trial starts
  • 4/1/2018 11:00:00 PM
  • First seeds drilled

    First seeds drilled
  • 4/8/2018 11:00:00 PM
  • Weeding undertaken

    Weeding undertaken
  • 4/8/2018 11:00:00 PM
  • Second seed drilling

    Second seed drilling
  • 4/22/2018 11:00:00 PM
  • Third seed drilling

    Third seed drilling
  • 4/29/2018 11:00:00 PM
  • Fourth seed drilling

    Fourth seed drilling
  • 5/2/2018 11:00:00 PM
  • First assessment

    First assessment
  • 6/9/2018 11:00:00 PM
  • Second assessment

    Second assessment
  • 7/23/2018 11:00:00 PM
  • Third assessment

    Third assessment
  • 8/30/2018 11:00:00 PM
  • Fourth assessment

    Fourth assessment
  • 10/14/2018 11:00:00 PM
  • Results analysis

    Results analysis
  • 11/15/2018 12:00:00 AM
  • Next steps

    Next steps
  • 2/1/2019 12:00:00 AM
  • Year Two of trial

    Year Two of trial
  • 3/31/2019 11:00:00 PM
  • First seeds drilled

    First seeds drilled
  • 4/8/2019 11:00:00 PM
  • Second seed drilling

    Second seed drilling
  • 4/22/2019 11:00:00 PM
  • Third seed drilling

    Third seed drilling
  • 4/29/2019 11:00:00 PM
  • Fourth seed drilling

    Fourth seed drilling
  • 5/2/2019 11:00:00 PM
  • First assessment

    First assessment
  • 6/9/2019 11:00:00 PM
  • Second assessment

    Second assessment
  • 7/23/2019 11:00:00 PM
  • Third assessment

    Third assessment
  • 8/29/2019 11:00:00 PM
  • Fourth assessment

    Fourth assessment
  • 10/17/2019 11:00:00 PM
  • Results analysis

    Results analysis
  • 10/31/2019 12:00:00 AM
  • Results discussion and next steps

    Results discussion and next steps
For further information hover over the above milestone marks
  • Discussion

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  • Achievements

    May 2020

    Final report

    The final report for the Hot Water Seed Treatment (HWT) field lab has been released, analysing the results from the 2018 and 2019 trials. Please sign in to view the full report - it is free to join the network.

    Overall, this trial provides some evidence that HWT can reduce levels of leaf spot on chard in the field and increase marketable yield:

    - In 2018, HWT reduced leaf spot and the proportion of chard unmarketable due to leaf spot, mainly for mixed chard

    - The 2019 trial did not demonstrate the benefits of HWT, but initial pathogen levels in the seed were much lower than in the 2018 seeds, therefore were unlikely to produce similar results. There was some limited evidence that HWT reduced seed viability in 2019. A third trial year would be useful for providing stronger evidence for in-field efficacy particularly in light of low pathogen levels in 2019

    - Swiss chard was generally lower in disease with a greater marketable and total yield than mixed chard

    Recommendations include:

    - Always test vegetable seed for pathogens before planting - not all will require HWT. Treatment may remove beneficial organisms and chemicals as well as pathogens and this should be considered in the case of very low pathogen levels

    - Using clean seed is the first stage in an integrated disease management approach but if tested seed does not have pathogens (or levels are very low) then it might not be economical to have it hot water treated.

    - If seed contains pathogens or if seed has not been tested, then consider HWT. Large scale commercial production should utilise commercial seed treatment; smaller scale and home-grown vegetable production can attempt DIY HWT using a water bath, but temperatures and timings must be exact

    - HWT penetrates the seed and is therefore effective in controlling pathogens that are inside the seed

    Milestone: Results discussion and next steps

    February 2020

    Results from 2nd year

    After the first year, there was a reasonable amount of evidence to suggest that treatment efficacy could translate into disease control in the field. However, this evidence was less clear in year two. This may be because the untreated control seed was very low in pathogen spore counts, so differences in pathogen levels between the treatment and control were low. This therefore limited the experiments comparison of a treated and untreated seed.

    The Group feel confident in applying the seed treatment each year to help protect the chard crop from leaf spot infection as part of an integrated disease management approach.

    Milestone: Results analysis

    September 2019

    New Innovative Farmers film with Riverford

    The second in the series of films telling the story of Innovative Farmers is now out. We caught up with growers at Riverford to see how their research has been going. Copy the link below into your browser to see why farmer led research like this is so important.

    Milestone: Year Two of trial

    March 2019

    First year results report

    The analysis of the first year data in this trial has been done, and the report is published and available on this page under "Field Lab documents" on the top right of the page - log in for free to access the documents.

    The review of 2018 results showed:
    • Seeds tested following HWST and prior to sowing showed 100% control of one pathogen (Alternaria), with less than 5% of seeds showing traces of the other two pathogens tested for (Cladosporium and Stemphyllium).
    • The treated plants yielded an average of 25t/ha of crop, compared to 22 if untreated.
    • 72% of the HWST crop was marketable on average, compared to 69% of the untreated crop.
    • This meant at a chard price of £2 per kilogram, using treated seed could offer an additional £5,910 per hectare of crop over the course of a season.
    • With reduced levels of disease, the crop is quicker to harvest, meaning a significant saving in labour costs.
    • The treatment primed the seeds and crops established quicker.
    • With reduced levels of disease, the crop is quicker to harvest and meaning a significant saving in labour costs.

    Ed Scott, Riverford grower, said: “The field lab results from last year were promising and found some benefits - the hot water treatment looks to be a useful tool in helping control leaf spot and improving crop yield. This also helps with labour savings as it is quicker to harvest the crops if there is less disease. However, 2018 was a particularly dry year with low levels of disease in general, so we are looking forward to comparing results to further trials this year.”

    Milestone: Results analysis

    August 2018

    Dry summer update

    The farmer has recently noted the following:

    "The drought has obviously been a major problem this year and inevitably we have already suffered some crop losses. It’s a real mixed bag with some crops failing like spinach and some thriving like onions and tunnel crops. The reservoirs are now dry but thankfully we had 42 mm of rain over a week ago and hopefully set to receive a bit more this weekend. The chard crops have been progressing quite well and we have been able to continue with the sampling followed by reasonable harvests. I am hopeful that we will be able to complete the full programme of chard trials and have some data to look at."

    Milestone: Third assessment

    July 2018

    Leaf spot monitoring

    The trial areas of both treated and untreated chard are now starting to show signs of leaf spot, which is later than expected probably due to the hot and dry weather. This may skew the results compared to a more 'normal' year, but will be factored into the final analysis.

    The farm has only had 3 inches of rain since 1 May, with only a few ml at each rain event. Despite being beneficial for the leaf spot, this has meant a lot of irrigation from reservoirs which may be at risk of running dry.

    The weights of chard with and without leaf spot are currently being taken continuously throughout the growing season across the four plots of drilled chard, and it is yet too soon to tell whether the hot water treatment has had an effect.

    Watch this space for results!

    Milestone: First assessment

    June 2018

    Proposal results

    The funding proposal for the field lab has been successfully accepted.

    Milestone: Proposal submitted

    June 2018

    Brush weeding

    The first plot of chard plots have been brush weeded to minimise the risk of weeds out-competing them. The farmer has noticed that the area that has been brush weeded seems to have more leaf spot spread through it, compared to where it hasn't been weeded and doesn't have leaf spot present. Cause does not mean effect, but this is an interesting observation to note for the trial.

    The chard drilled later on looks healthier and less weedy, which the triallist thinks is potentially because they are coming into a staler seed bed.

    Milestone: Weeding undertaken

    June 2018

    Establishment progress

    The chard has in places struggled to establish, possibly due to issues with the drill as this seems to be worst at the beginning of the drilled rows. A couple of rows have unfortunately been lost to weeds, but this has not significantly affected the trial area.

    Milestone: Fourth seed drilling

    April 2018

    Chard drilled

    The chard is being drilled as part of a 5 year rotation after salads and will be followed by a 3 year ley. The farmers noticed the first leaf spot 3 years ago, and as it can significantly affect the saleable crop, they are looking for solutions to reduce its effect.

    All 4 plots of chard have now been drilled for the season and the data collection will start periodically as each row of crop matures for harvest.

    Milestone: Fourth seed drilling

    January 2018

    Methods progression

    The group met with researcher Dominic Amos to clarify questions on the methods and discuss the trial layout. Two varieties of chard have been decided upon to trial with. The programme of drilling the chard seed will be driven by the vegetable box requirements, as ordered by customers. The seed has already undergone the hot water treatment (HWT) of which the majority have been treated, with the remaining left for control comparisons.

    For practical purposes, the box used to gather the chard for harvest will be used as an area measurement of the crop to assess. This will be done multiple times across the field in order to gain replicability and more scientifically robust results. It will also be undertaken several times throughout the growing season, however it would be unfeasible to do so every week.

    A scale will be decided upon to rate the amount of leaf spot. There will also be help from Dominic on several occasions to help gather the data where the farmers are too busy in the peak of the season to do so.

    Photographs will be taken to help record the amount of leaf spot on each sample harvested, and can be used later on in the trial to help evaluate the effectiveness of the treatment.

    The coordinator mentioned that brush weeders need to be planned in to the process. The methods discussed above will be further crystallised over the next month between the farmer and Dominic Amos.

    Milestone: Methods planning

    November 2017

    Field lab planning

    The farmer interested in trialling hot water treatment met again with the researcher and Innovative Farmers representative to discuss how to progress with the trial. Initial method ideas were laid out for the following spring, with discussion around how to progress with the trial.

    Initial method ideas were laid out for the following spring, including:
    - Comparing treated vs untreated seed but otherwise crop grown to normal commercial methods
    - Recording seed tests results before and after hot water treatment
    - Crop germination/establishment
    - Crop assessed for disease levels (by % leaf area affected) correlated to picking rate
    - Indication of weeds present
    - Soil tested for pathogens pre and post seed drilling.

    The group are considering trialling with a chard crop

    Milestone: Initial meeting

    September 2017

    Initial ideas meeting

    This meeting was for growers from Riverford and South Devon Organic Producers. At this meeting around 8 ideas for field labs were discussed and then narrowed down to 5 strong contenders. The coordinator helped to narrow down the ideas, one of which was to treat seeds susceptible to developing leaf spot via microbial disease with hot water prior to germinating and planting.

    The source of leaf spot has not yet been clearly identified by researchers or farmers, and can come from a variety of bacterial and fungal sources. This field lab will therefore concentrate on treating the seed to eliminate the possibility of it being carried on the seed prior to planting. This will help identify where the source of disease is, as well as potentially providing a solution to it.

    One farmer in particular is interested in trialling this method, and as it is expensive it may be that it is trialled initially with one farmer with the view to expanding the group next year if the results are encouraging.

    Milestone: Idea formation

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