Abstract
Mainly in Anglo-Saxon countries (USA, New Zealand etc.) the market for organic agriculture inputs offers different natural substances for the use as bio-herbicides. The most important ingredients of these products are acetic acid, citric acid and clove-extracts (eugenol) in the case of post-emergence herbicides and corn-gluten in pre-emergence products. In a first screening test we compared the efficacy of these ingredients with some other natural substances. The most interesting ones were later compared in a field trial where the efficacy and the required dosages to clean a strip of about 40 cm under the trees were assessed in an apple orchard. A few products showed interesting results (vinegar, pine oil), but the required dosage to keep the strip under the trees clean was mostly very high.