Use of botanicals to protect early stage growth of hop plants against Pseudoperonospora humuli

Abstract

Constantly increasing pressure to implement the principles of integrated production of hops results in the need for new plant protection products. Various plant extracts, also called botanicals, have potential to be used as alternatives to conventional pesticides. In three-year field trials on virus-free seedlings of Saaz hops, the efficacy of thyme essential oil, hops extract and algae extract against hops downy mildew (Pseudoperonospora humuli) was investigated. Different concentrations (0.5–1%) of plant extracts were applied to the hop plants six times during vegetative growth, and the degree of damage caused by P. humuli, the health condition and the chlorophyll content in the hops were evaluated after selected applications. All botanicals demonstrated very good antifungal properties comparable to treatment with commercial fungicides. Even one dose of plant extract was able to significantly suppress disease development for two months compared to untreated control. Thyme oil (0.5%) was considered to be the most effective botanical. Not only did it have good antifungal properties, but it also had positive influence on the chlorophyll content (up to 30% increase). These trials have shown that all botanicals tested have the potential to be used in an integrated, ecological hop production system.