Effects of wheat undersowing and sweet alyssum intercropping on aphid and flea beetle infestation in white cabbage in Germany and Japan

An undersowing system with additional intercropping of fowering plants was assessed in feld trials in Germany and Japan to estimate regulating efects on pests and possible negative efects on white cabbage (Brassica oleracea var. capitata). In particular, we tested cabbage undersown with wheat (Triticum aestivum L.) and cabbage undersown with wheat plus additional sweet alyssum (Lobularia maritima L. Desv.) intercropping. Counts of the aphid species Brevicoryne brassicae (L.) and Myzus persicae (Sulzer), as well as related predators on cabbage plants, were determined. Abundance of Phyllotreta spp. fea beetles and their feeding damage on cabbage plants were recorded and cabbage yield was compared. In both countries, trials showed that wheat undersowing reduced the abundance of M. persicae but not B. brassicae. The occurrence of natural enemies on cabbage plants was not signifcantly afected by any of the companion plants. Additional sweet alyssum intercropping increased the abundance of adult hoverfies at the German but not at the Japanese location. However, it also signifcantly increased fea beetle infestation on cabbage plants at both locations. Neither wheat undersowing nor additional sweet alyssum intercropping signifcantly reduced cabbage harvest weight. In conclusion, adding companion plants can be a promising method to improve pest control in vegetable crops. However, intercropping crucifer crops with sweet alyssum may not be recommended in regions where fea beetles are a relevant pest because of the observed enhancing efect on them. In contrast, to prove the positive efect of wheat undersowing on white cabbage, results from further years of investigation are needed.