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Kaolin – Effective against Drosophila Suzukii in Vineyards without Any Impact on Wines

Article in Vitis, Journal of Grapevine Research

Kaolin was tested in viticulture to control the dreaded pest Drosophila suzukii. The trials showed that this natural product has a comparable efficacy to conventional insecticides without any adverse effect on wine quality.

Since 2014, the Spotted-wing drosophila (Drosophila suzukii) has been causing substantial damage in Swiss vineyards. To counter this threat, insecticides are used in a strictly circumscribed manner. Nevertheless, winegrowers are reluctant to apply insecticides just before grape harvest due to residue issues and potential loss of image. Pest control thus relies primarily on prophylactic measures, particularly on proper aeration and lighting of the grape zone. The use of kaolin, a chemically inert white rock powder based on aluminosilicate, may constitute a valuable alternative to insecticides. The particles of this mineral stick to the surface of the grapes, forming a physical barrier that reduces damage. However, the impact of multiple kaolin applications shortly before grape harvest on the chemical and organoleptic properties of the wines produced is poorly documented. This article presents a synthesis of our results concerning the efficacy of kaolin against D. suzukii as well as the effect of its use on the chemical and sensory properties of wines.

Kaolin applied on different grape varieties

To control D. suzukii, kaolin (Surround WP®) was applied in 23 field trials on different grape varieties in several wine regions of Switzerland in autumn 2016 (Fig. 1). Comparable to conventional insecticides, kaolin had an overall efficacy of 54%. Moreover, no significant differences were observed between applications of kaolin at concentrations of 1% and 2%.

Figure 1. Grape clusters treated with kaolin. (Photo: Christian Linder, Agroscope)

Quality of ‘Mara’ red wines unaffected

In addition, a wine-quality trial was conducted with the red grape variety ‘Mara’. This trial revealed that three applications of 1% or 2% kaolin did not affect fermentation or the chemical properties of the wines compared to an untreated control. The aluminium concentration in the wines rose slightly with the applied dose of kaolin, but remained nearly 40 times lower than the tolerated threshold. Furthermore, tasters were unable to distinguish between the wines produced from grapes treated with kaolin and the untreated (control) wine.

Conclusions

  • Approved for use in organic farming, kaolin ensures satisfactory protection of grapes against D. suzukii.
  • This natural product poses no problem in terms of residues or resistance.
  • Its impact on beneficial organisms is negligible.
  • The chemical and organoleptic properties of the red grape variety ‘Mara’ were not affected.
  • The results of this study show that kaolin applications are effective against D. suzukii and do not pose major risks to the environment, wine quality or human health.

Scientific article

Kaolin – Effective against Drosophila Suzukii in Vineyards without Any Impact on Wines

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