Dual role of milk on aphid and powdery mildew control in kale

Powdery mildew (PM) is the most important kale disease and it is more difficult to manage when plants are simultaneously infested with aphids. In this work, we aimed at evaluating the contribution of a sulphur-based fungicide, water, or cow's milk to control PM as well as the aphids Brevicoryne brassicae and Myzus persicae on kale under greenhouse conditions. We also assessed in vitro the effect of the products mentioned on their selective action on growth of the entomopathogenic fungus and the aphids. Four week-old plants naturally infested with aphids and PM were evaluated for disease severity and aphid counts. Plants were sprayed weekly with milk (10% v/v), sulphur (2 g/L), or water. From 7 to 28 days after the experiment onset (DAEO), plants were evaluated weekly for the disease severity, number of each aphid species, and number of fungal-colonized dead aphids. Milk and fungicide sprayed on plants reduced disease (30% and 10%, respectively) compared to the water control (P ≤ 0.001). In addition, B. brassicae population was reduced for the milk but not for the fungicide treatment at 21 DAEO. Surprisingly, the dead aphids were parasitized by a fungus identified as Cladosporium cladosporioides. Moreover, milk treatment did not interfere with C. cladosporioides in vitro growth. On the contrary, sulphur, copper oxychloride, and azoxystrobin reduced fungal growth. Additionally, C. cladosporioides, milk, and milk + C. cladosporioides reduced B. brassicae and M. persicae populations. A dual role of milk on both powdery mildew and aphid control reinforces the usefulness of this product on glasshouse kale production.