Courgettes: Review of blossom end rot - causes and potential solutions

The Problem:

Currently, a problem that has been termed ‘blossom end rot’ results in considerable yield loss in courgettes year on year. No formal work has been carried out to investigate the problem in the UK, and as a result the exact cause of this problem is undefined. Traditional blossom end-rot (BER) is categorised as a ‘physiological disorder’ which is linked to a localised calcium deficiency in the distal part of the fruit.  This could be the cause of BER in courgette, but the standard practice of flower detachment from the end of the courgette after fruit set could also introduce pathogens to the fruit through the flower scar. Growers have reported that damp, humid conditions exacerbate the problem; damp flowers can adhere to the fruit and lead to rapid break down.

Localised calcium deficiency in the fruit can also be linked to the weather (e.g. dull, humid conditions, followed by bright sunshine).  Calcium is dissolved in water and taken up passively (osmosis) by the root system. When the plant is growing rapidly under high sunlight and temperatures following a period of relative inactivity (e.g. dull conditions) the plant is less able to rapidly translocate calcium from the root in sufficient quantities to match the demand from the growing fruit tissues. It could be that a combination of the two factors are contributing to the BER losses observed in the field. Crop husbandry factors which include variety, soil structure, root health, fertiliser and pesticide applications may also play a role in the development of courgette blossom end-rot. A review of the problem and potential causes will be carried out to identify practical techniques that could be implemented to mitigate against BER. Overseas research and technical advice will be sought, as the problem is reported to be less common; these courgette crops are predominantly grown either under protection or in drier conditions compared with open field production in the UK. A final report will be delivered which will identify the plant, husbandry and environmental factors which could be involved and action identify potential solutions; the work may also identify that further research is required to identify practical solutions under UK conditions.

Benefits to industry:

• The causes of the problem are identified
• Practical intervention could be identified for immediate uptake by the growers
• Reducing losses to BER would increase revenue and marketable yield
• Would allow information from a range of sources e.g. UK and overseas growers and from other crop types with significant BER yield losses into a single point of reference.
• Options would be explored from the growers perspective, ensuring suggested control options are practical and cost effective
• Results would be collated in a final report
• An article would also be written for HDC news, and a presentation given at an appropriate outdoor cucurbit event

Aims and objectives:

Project aim(s):

To utilise scientific literature, technical information from both the UK and abroad and specialist grower knowledge to deliver a series of potential solutions to the problem of blossom end rot in courgettes.

Project objective(s):

1. To define the problem of blossom end rot in courgettes and its incidence through grower liaison and review of technical literature.
2. To carry out a literature review covering potential causes of the problem, (covering both nutrition and disease) and exploring treatment/alleviation options from the UK and overseas, which will include information from other crops.
3. To critically evaluate potential solutions for immediate uptake by courgette growers.