Results - short version
Since the start of the demonstration project in 2017 up to 22 producers of cherry, raspberry, blackberry and blueberry have been taking part each year. The farms are located in Baden-Wuerttemberg, Lower Saxony and North Rhine-Westphalia. The mesh sizes of the nets used varied between 0.8 x 0.8 mm and 1.3 x 1.3 mm. Cherry cultures were covered with foil canopies and netted laterally. Berry cultures were equipped with foil tunnels in combination with nets (laterally or covering the whole tunnel) or covered with nets only.
Spotted Wing Drosophila Drosophila suzukii
In every project year, the nets have proven to be highly efficient in excluding D. suzukii: none or only very few adult Spotted Wing Drosophila (SWD) were found in bait traps. Likewise, no or only low numbers of infested fruits were found within the netted orchards. This was evident especially in late fruit cultures, when fly population pressure was increasing. For netted cherry orchards, limited conclusions could be drawn for the years 2017 and 2018, as SWD population growth was slow and delayed due to cold winter conditions, frost periods in early spring, followed by repeated periods with temperatures >30 °C and continuous dryness in summer. Nevertheless, clear reduction in damage levels in comparison to cherry cultures without net protection were obvious.
In comparison to conventional fruit production, the number of insecticide treatments against SWD was markedly reduced under net covers. Treatments declined over the years in several cases even to zero as farmers relied more and more on the regular monitoring performed by the project collaborators in charge.
Other pests and beneficials
There was no noticeable increase in occurrence of other pests with the exemption of higher levels of spider mite infestation in some cases. However, this mostly occurred in foil tunnels and under foil canopies with limited ventilation in the roof area. There, the higher temperatures obtained on sunny days enhanced population growth of thermophilic spider mites. It is most important to continuously monitor the incidence of other pests in the netted crops as – when they occur – they can develop rather undisturbed since antagonists cannot enter the system. Monitoring of beneficials showed low numbers in the netted crops, but there were no obvious differences compared to the open field situation.
In order to obtain continuous yield of high quality raspberries in netted cultures, pollinators, usually bumblebees have to be introduced on time and in sufficient numbers. This is also necessary in cherries, if the nets are closed before or during bloom.
The project clearly proved the importance of closing the nets in time, i.e. the latest with onset of fruit colour change. Moreover, the project also showed, that using only lateral netting is critical for successful management of D. suzukii.
With regard to the technical implementation, particular problems were revealed and improvements were undertaken: how to achieve a tight ground connection of the lateral nets; to use sandbags instead of rough stones as weights for the ground fixation in order to avoid damages to the net due to friction; how to safely close and connect net parts; how to avoid chafe marks using buffers, how to improve the entrance areas so that quick opening and closing of the net is possible.
Temperature and humidity recording with data loggers showed negligible differences between netted and open crops. Greater deviations, especially increased temperatures on days with strong insolation, occurred in berry cultures in netted foil tunnels without openings in the roof area. In these cases, however, the foil tunnel was the main cause for the temperature increase, not the net.
Additional costs for exclusion netting vary and are determined by factors such as crop type, geometry of the orchard, the netting system used, if the netting is a completely new construction or a supplement to an existing construction, and by the amount of contributions by the growers themselves. According to the analysis in the participating farms, the acquisition costs for the netting amounted on average to 4.400 €/ha, and 7 € per running meter. Depending on the technical implementation and the various factors mentioned above the acquisition costs (net, auxiliary equipment, first montage) fluctuated between 2.600 €/ha and 15.000 €/ha. The costs of the net amounted on average to 61% of the prime costs. However, as SWD infestation occurs regularly, yield losses in unprotected fruit crops quickly exceed these additional costs.
For more details refer to:
Augel, C.; Boehnke, B.; Wichura, A.; Lindstaedt, J.; Wiebusch, J.-H.; Engel, A.; Benz, S.; Saltzmann, J.; Eberhardt, G.; Vogt, H.; Köppler, K. (2020): Demonstration project "Exclusion netting for managing Spotted Wing Drosophila in fruit crops" – Results 2017 – 2019. In: Foerdergemeinschaft Oekologischer Obstbau e.V. (FOEKO) (Hrsg.): Proceedings of the 19th International Conference on Organic Fruit-Growing: from February 17th to February 19th, 2020 at the University of Hohenheim/Germany, 166-169.
Boehnke, B.; Köppler, K.; Augel, C.; Wichura, A.; Lindstaedt, J.; Wiebusch, J.-H.; Engel, A.; Benz, S.; Vogt, H. (2018). Demonstration project "Exclusion netting for managing Spotted Wing Drosophila in fruit crops" – Results 2017. In: Foerdergemeinschaft Oekologischer Obstbau e.V. - FOEKO [Hrsg.]: EcoFruit: 18th International Conference on Organic Fruit-Growing; Proceedings to the Conference, 19.02. - 21.02.2018 at Hohenheim/Germany, 268-271.
Boehnke, B.; Köppler, K.; Augel, C.; Wichura, A.; Lindstaedt, J.; Wiebusch, J.-H.; Engel, A.; Benz, S.; Vogt, H. (2019): Demonstration project "Exclusion netting for managing Spotted Wing Drosophila in fruit crops" – Results 2017. In: Linder, C.; Fountain, M.; Prodorutti, D. (Hrsg.): Working Group "Integrated Protection of Fruit Crops", Subgroup "Soft Fruits": Proceedings of the 9th Workshop on Integrated Soft Fruit Production at à Riga (Latvia), 5-7 September 2018 (IOBC WPRS Bulletin 144), Darmstadt, 78-84
Annual Reports (in German)
Ergebnisbericht 2017 Demonstrationsvorhaben „Einnetzen von Obstkulturen zum Schutz gegen die Kirschessigfliege (Drosophila suzukii)"
Ergebnisbericht 2018 Demonstrationsvorhaben „Einnetzen von Obstkulturen zum Schutz gegen die Kirschessigfliege (Drosophila suzukii)"
Ergebnisbericht 2019 Demonstrationsvorhaben "Einnetzen von Obstkulturen zum Schutz gegen die Kirschessigfliege (Drosophila suzukii)"
Ergebnisbericht 2020 Demonstrationsvorhaben "Einnetzen von Obstkulturen zum Schutz gegen die Kirschessigfliege (Drosophila suzukii)"
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