Push (-and-pull) strategy with sage extracts may reduce crop losses caused by the cabbage root fly, Delia radicum
The cabbage root fly (CRF, Delia radicum, Diptera: Anthomyiidae) is the major insect pest in vegetable brassica crops. It is native to Europe and well established in North America. Its larvae damage the host plants above- and/or belowground, resulting in plant mortality and yield loss. Since the revocations of the major insecticides, the economic threshold decreased and integrated pest control has become more important to limit infestation of the CRF. Hence, the quest for alternative crop protection approaches has become a top priority. The European project FlyIPM aims to study these alternative approaches individually and in combination to design integrated cultivation practices and provide growers with recommendations on how to best manage CRF. As part of the European Project FlyIPM, we tested push (-and-pull) strategies. We performed a series of greenhouse and field experiments to address the following questions: 1) Do sage extracts repell the egg-laying of the CRF? 2) Which kind of sage extract is more efficient in reducing egg-laying of the CRF? 3) Does rutabaga juice stimulate landing and egg-laying of the CRF? Nottingham (1987) and Hirschfeld and Klingauf (1988) previously showed that sage extract can be used as a push component to manipulate the egg-laying of the CRF. In experiments conducted in 2016 using a vegetable brassica-based diet (Vogler and Boeriis, 2019), we confirmed a repellent effect of sage extracts. Here, greenhouse trials with potted plants and field trials were carried out. We expected fewer eggs laid on plants treated with sage extract than on the untreated control plants, whereby different types of sage extracts were tested. The repellent effects of the different types of sage extracts were not as strong as expected in the greenhouse and field trials. The rutabaga juice stimulated the landing and egg-laying of CRF. However, only short-term effects, just after treating the plants were observed. No long-term effects could be detected with the tested formulations. The push (-and-pull) strategy remains, in our opinion, a promising alternative method, but there needs improvement of the timing and frequency of the treatments as well as of the deployment of behaviourally active stimuli.