Tuesday, 6 July 2021
Are protective sprays necessary to prevent Botrytis and grey mould in covered table-top strawberry production? Scott Raffle explores why fungicides may not always be required.
In the days of open field-grown strawberry production, before protective tunnels had ever been thought of, the success of the short season could often be measured by the volume of rain that fell during the period of ripening. This generally started in late May in the South of England and finished in late July in the North of Scotland.
Wet, warm and humid weather in soil-grown crops generally gave rise to a high incidence of grey mould caused by infection from the fungal pathogen Botrytis cinerea. The spores from this pathogen land on the stigma of the strawberry flower and germinate down the style into the ovary, setting up an infection. This can sometimes remain latent until favourable conditions lead to the spread and development of the characteristic dusty grey spores which cover the ripening fruits, causing a soft rot to develop.
Strawberry growers were advised to apply protective fungicides to the newly opening flowers during the blossom period, which helped protect them from infection. This reduced the incidence of rotting and the resulting yield losses.
However, with the advent of protected cropping on tabletops, which support the crop at a considerable height above the soil level, the incidence of Botrytis infection and subsequent grey mould appears to have declined. Many growers and agronomists were curious to find out if protective sprays were therefore necessary in this type of cropping system.
Can good growing practices prevent Botrytis instead of fungicides?
We looked at novel approaches to both powdery mildew and Botrytis control in tunnel grown strawberry on tabletop supports.
In field trials in 2018 and 2019 on bag grown everbearers, there was little benefit found in applying fungicides specifically for Botrytis control only, compared to untreated control plots.
Some growers still like to use fungicides to control other pathogens such as Mucor and Rhizopus, which also lead to soft rots, but our research demonstrated that their use only achieved a small reduction when compared to untreated plots. Therefore, you need to consider the full benefits carefully before choosing to spray.
The research showed you could safely rely on growing under protection and good use of cool-chain management to prevent any latent Botrytis infection from developing into visual rots during the post-harvest shelf-life period.
Good management of fruit waste at harvest to control spotted wing drosophila will also help to minimise Botrytis infection and other soft rots caused by Mucor and Rhizopus.
I would therefore encourage you not to rely on fungicide use for Botrytis control on protected tabletop strawberries. This will help to reduce the risk of fungicide residues occurring and also reduce production costs.
Scott has worked for AHDB for 11 years, having spent three years at HDC and 30 years in the fruit industry in total. Prior to his time at AHDB, Scott was a fruit advisor/agronomist for 16 years with ADAS, specialising in soft fruit and apple and pear storage.