Miljøprojekt, 997 – Net-afdækning som alternativ til kemisk bekæmpelse af skadedyr i kålafgrøder

Net-afdækning som alternativ til kemisk bekæmpelse af skadedyr i kålafgrøder

Summary and conclusions

Covering of soil to prevent pests, as an alternative to chemical control in cabbage crops.

Introduction

During the summer the cultivation of cabbage crops without pesticides can be very difficult because of cabbage root fly attack. Covering with insect nets (woven polyethylene material) or fleece (non-woven polypropylene material) can prohibit attack, but will also alter the climate (temperature and humidity) under the covering material. Especially in cauliflower, high temperature can give problems with physiological development such as curd initiation, bracting (small leaves growing through the surface of the curd), loose curds, and hollow stem. High humidity, on the other hand, may cause high risk of disease attack.

Material and methods

Field experiments with five different covering materials were performed in two years (2001/2002), to investigate the effects on development and quality of cauliflower in summer/autumn growing. Two 17 g m^-2 fleece (Lutrasil and Sivatex), two thin fleece products (Covertan 12 g m^-2 and Agryl P10 g m^-2 reinforced), two insect nets of 60 g m^-2 (Rantai and Bionet) and a control test without any covering were included in a randomised design with three replicates. Two cultivars (Nautilus and Fargo) were tested in every replicate. The temperature and humidity under the nets and fleece were measured every 10 minutes at 20 cm height. In a second experiment, three different cultivars (Amerigo, Devina, Siria) that are claimed to be resistant to high temperature, were tested under fleece 17 g and insect net (Rantai). Cultivar Nautilus and no covering were used as control plots. Samples of cauliflower were taken at about two weeks' interval to follow the development and curd initiation. At harvest the cauliflower was assessed for curd quality and disease attack.

Results

The results showed that the fleece products Lutrasil and Sivatex raised the average mean temperature during the growth season by 1.1 °C and 2.1 °C, respectively. This temperature rise was enough to cause a serious delay in curd initiation (up to 10 days) and gave severe bracting in the harvested cauliflower (up to 60% of curds). The thinner fleece products Covertan 12 g and Agryl P10 showed a lower mean temperature rise of 0.5 °C, but this was also sufficient to give physiological problems in the development of the curds. The fleece products all had higher incidences of disease attack and rotting due to high humidity. The two insect nets Rantai and Bionet only raised the mean temperature by 0.1 °C, and there was no significant difference in the development and quality of the cauliflower compared to the control plots. The cultivar Amerigo was high-temperature tolerant but, on the other hand, had problems with disease attack.

Conclusion

The conclusion from the experiments is that in the summer cauliflower production without pesticides, it is necessary to use the rather expensive insect nets instead of fleece products, in order to ensure stabile high quality produce.