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Tackling Post-Harvest Storage Losses

Apples are ranked the number one fruit by purchasing volume per household in the EU and apple farmers across Europe are benefitting from a predicted 9% increase in demand this year. A consequence of the pandemic is that air cargo transport limitations have reduced the supply of tropical fruit, causing consumers to opt for popular, local choices, such as apples. While this year’s apple harvest has come to a close in many areas, the harvest of some varieties, such as France’s Snow apple, has only recently begun.  

Although the boost in demand in 2020 is very much a positive for apple farmers, it has added pressure on the supply chain at a time when growers across Europe have already been challenged with a difficult season and reduced yields. For example, in Belgium the apple harvest has been roughly halved, primarily due to damage caused by frost and sun earlier in the season. 

Post-harvest diseases

Climatic conditions can physically damage apples but they can also rapidly increase the spread of fungal pathogens. This is particularly apparent in North Western Europe, where mild and humid conditions favour fungal diseases, such as Apple scab and Apple Bitter Rot. 

These fungal pathogens can be devastating for farmers, as early symptoms can often go unnoticed; the extent of the disease only becoming evident post-harvest, when apples are in storage. At this stage, fungal pathogens can spread rapidly; a few apples with spores will be enough to start the progression of a disease throughout the storage unit, destroying a large proportion of the harvest. Farmers try to reduce the spread of post-harvest diseases in the storage stage by managing storage climate but it is near impossible to control the diseases effectively, due to the long storage period for apples.

Consequently, it is not uncommon for a significant portion of a harvest to be lost to post-harvest diseases on organic farms. Even in non-organic systems, where fungicides are used regularly, farmers will expect to lose about 10-25% a year. A study into the impact of post-harvest diseases on Cripps Pink apples (commonly sold as the Pink Lady variety) found that storage diseases caused an economic loss of up to €450 per tonne. This indicates that the spread of post-harvest diseases can ultimately make or break a farmer’s year. 

In addition, considering increasingly volatile weather conditions caused by climate change, post-harvest diseases are likely to become more of a problem in the future. Many post-harvest diseases are spread through rainfall and develop more quickly in humid conditions. Climate change will intensify periods of rain, facilitating the spread of fungus. 

Managing the spread 

Post-harvest diseases are not a new phenomenon for apple growers and much work has gone into developing disease management strategies. To fight post-harvest diseases, farmers must ultimately answer two questions; how do I reduce the spread of fungus in the orchard? And, how do I reduce the spread just before harvest, to minimise pathogens entering the store? 

Integrated Pest Management

All growers must have an Integrated Pest Management (IPM) programme in place. This ensures integration of best practice and combination of methods to control pests and disease. It considers:

   - Economic constraints
   - Legal requirements
   - Sustainable pest and disease control
   - Fruit yield and quality
   - Minimisation of risk to growers, consumers and the environment

Orchard health and tree performance

Ensuring trees are vigorous and can withstand both biotic and abiotic stresses better is the first step in tackling disease. This requires:

   - Suitable fertiliser programmes 
   - Maintaining healthy soil, with high biological activity
   - Managing distance between rows of trees and regularly pruning trees to ensure good canopy structure and air flow.
   - Removal of decaying material 

Actions leading up to harvest

   - Minimising physical damage. When apples are ripe, the skin is stretched and can be more prone to breaking, which acts as an entry point for pathogens. 
  - Careful monitoring for pests and disease 
   - Considered use of pesticide sprays

Plant protection products play a significant role in controlling disease during the critical stage before harvest and farmers regularly spray apples in these last weeks before harvest. A 2016 study by DEFRA confirmed that on average, apple orchards in the UK receive over 16 spray applications a season, the majority of which are fungicides. 

Maximum Residue Limits (MRLs) for harvested produce means that the available choice of effective fungicides is limited for use close to harvest. The pre-harvest interval (PHI) for many conventional chemistries effectively removes them as an option for late season applications.  

Furthermore, the overall choice of fungicide options to combat post-harvest diseases is dwindling. 

A growing number of products has been taken off the market as part of a wider movement to reduce the use of chemical fungicides in farming. One factor behind this move is that post-harvest diseases are becoming more resistant to chemical controls. For example, it has been widely reported that Apple Bitter Rot has developed strong resistance to some commonly used fungicide active ingredients.

The potential of bio-fungicide solutions

Bio-fungicides, such as Eden’s Mevalone product, can provide farmers with an effective and sustainable way of fighting post-harvest diseases, with applications at the most critical timings, right up to the point of harvest. A key differentiator for Mevalone is that it has a PHI of just 1 day and is MRL-exempt, making it an invaluable part of IPM programmes. In addition, the terpene active ingredients in Mevalone are considered to have multisite activity, with no known resistance, meaning that development of resistance is unlikely.

The use of products such as Mevalone will ultimately result in fewer synthetic chemical-residues ending up on our supermarket shelves, which is critical for retailers and consumers alike. 

A key challenge for farmers currently is the lack of efficacious bio-fungicides readily available in the market, which severely limits their choices when trying to combat post-harvest diseases.  However, the regulatory approval process is being aligned with farmers’ immediate needs and the consumer’s desire for chemical-free food, which will benefit all stakeholders. French regulators have previously granted 120-day emergency use approval for Mevalone on apples, which demonstrates the importance of such products to the industry. Full product approval in France is now pending.

The application for bio-fungicides based on natural chemistry is vast, and Eden is poised to embrace the huge opportunity and contribute to sustainable crop protection, to help farmers achieve their harvest potential.  

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