Preventing sunburn in redcurrant and cherry
Source: De Fruitteeltkrant, writer and editor are listed under the article.
By choosing the type of film, the temperature underneath it - and thus the risk of sunburn for redcurrants, raspberries or cherries grown under film - can be reduced. The Dutch supply company Vlamings carried out temperature measurements under various types of film on redcurrants. The measurements showed a temperature difference of 4°C on hot days, according to the presentation by Vlamings advisor Lars Wijnen during the digital Kennisdag Kleinfruit & Steenfruit this spring. The reason for the study was the major problems with sunburn damage to redcurrants in 2019. At three red berry farms in North Brabant, several PE films of the same thickness but with different additives were compared with the standard film used in red berry cultivation in 2020. In the case of the extra diffuse tunnel film, the film allows more diffuse light and less direct sunlight to reach the crop. Another type of film, known as 'cool', is more concerned with a heat-retarding effect, without affecting the transmission of light.
Temperature measurements
During the heat wave, on the hottest day, 8 August 2020, the temperature rose to almost 50 °C under newly installed standard film. This temperature caused sunburn damage to the berries. In red currants, but also in cherries, significant sunburn damage already occurs if the fruit temperature exceeds 45 °C for more than one hour. In one of the test plots, the temperature rose to 48.6 °C in the afternoon under newly installed standard film. Under standard 8 year-old film, which allows less light through due to pollution over the years, the temperature rose to 46.7°C. This is a difference of almost 2°C. This is a difference of almost 2 °C. Under the extra diffuse foil, the temperature rose to 44.9 °C. Under the
foil designated as 'cool', the temperature rose to a maximum of 44.8 °C. The difference of four degrees is considerable.
Opting for alternative foil
Wijnen advises fruit growers with plastic shelters to take the effect of sunburn into greater consideration when selecting the type of film. According to the supplier, the additional costs of the new film types are insignificant compared to the extra heat damage caused by standard films. According to the supplier, the type of film to be selected depends on the maturity period of the crop grown under it. The extra diffuse tunnel film is particularly interesting if harvesting takes place in June/July, when radiation intensity is at its highest. For crops harvested in August, the film type 'cool' is preferred. This type of film keeps the heat out of the crop better without blocking much sunlight.
Author: (Wouter van Teeffelen, WTE Fruitadvies) Editorial: (Gerard Poldervaart, De Fruitteeltkrant)