Control of late blight of potato with medicinal plant suspensions

Suspensions and extracts of medicinal plants reduced foliar blight of potatoes (Phytophthora infestans) significantly in wet room experiments. The efficacy of finely ground plant material sprayed as aqueous suspensions was comparable or better than the ethanolic extracts. With aqueous suspensions the time consuming ethanolic extraction is avoided and environmental pollution with solvents during the field application is reduced. Best results were obtained with the root of medicinal rhubarb (Rheum palmatum) and the bark of buckthorn (Frangula alnus). However, the good results of the wet room experiments could not be confirmed in field trials. The protective effect of the best extracts and suspensions was insufficient in the field trial and did not reach the efficacy of copper treatments.