Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2002
Publication Date: N/A
Interpretive Summary: Weeds are a major pest problem in U.S. agriculture, causing up to 12% loss in crop yield worth nearly $ 33 billion. Organic farmers cannot use synthetic herbicides and weed infestations result in costly crop losses. Herbicides for organic systems are limited and new weed control tools are needed to help maintain economic viability of organic farmers. Dilutions of essential oils of cinnamon, clove, summer savory, and red thyme were determined to kill shoots of troublesome weeds (johnsongrass, lambsquarters, and ragweed) that are commonly found in fruit orchards. The weed-killing component of cinnamon oil was identified as eugenol, a compound used as a dental antiseptic for analgesic purposes. Essential oils are extracted from plants and thus may be useful as a "natural product herbicide" for organic farming systems. Field experiments are being conducted to evaluate eugenol as a herbicide beneath fruit trees.
Technical Abstract: Laboratory and greenhouse experiments were initiated to determine the herbicidal effect of plant-derived oils and identify the active ingredient in one oil with herbicide activity. Twenty-five oils were applied to detached leaves of dandelion in the laboratory. Essential oils (1 % v/v) from red thyme, summer savory, cinnamon, and clove were most phytotoxic and dcaused electrolyte leakage resulting in cell death. These essential oils plus two adjuvants (Silwett L-77 & Superior oil at 0.2% (v/v)) were sprayed on shoots of lambsquarters, common ragweed, and johnsongrass growing in the greenhouse. They caused shoot death within 1 hour to 1 day when applied at aqueous concentrations from 5 to 10% (v/v). Essential oil of cinnamon had high herbicidal activity and eugenol (2-Methoxy -4-(2-propenyl)phenol) was determined to be this oil's largest component (84%). Dandelion leaf dish and whole plant assays verified that eugenol was the active ingredient in essential oil of cinnamon. Essential oils are extracted from plants and thus may be useful as a "natural product herbicide" for organic farming systems.