Phytotoxicity of Clove Oil to Vegetable Crop Seedlings and Nematotoxicity to Root-knot Nematodes

Authors: Meyer, Susan; Lakshman, Dilip; Zasada, Inga; Vinyard, Bryan; Chitwood, David

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2008
Publication Date: 12/31/2008
Citation: Meyer, S.L.F., Lakshman, D.K., Zasada, I.A., Vinyard, B.T., Chitwood, D.J. 2008. Phytotoxicity of clove oil to vegetable crop seedlings and nematotoxicity to Root-knot Nematodes. HortTechnology. 18:631-638.

Interpretive Summary: Plant-parasitic nematodes are microscopic worms that cause ten billion dollars in U.S. crop losses annually, and root-knot nematodes are among the most destructive species on vegetable crops. Growers would benefit from new, safe and effective methods for reducing crop losses caused by these nematodes. Because the natural substance clove oil is active against other organisms that cause plant diseases, this plant product was tested as a possible management agent for the root-knot nematode. Clove oil at certain concentrations was found to be phytotoxic to cucumber, muskmelon, pepper and tomato seedlings, and the tested formulation of clove oil did not consistently reduce populations of root-knot nematode on cucumber plants. The results are significant because they demonstrate the difficulties in utilizing this essential oil as a nematicidal natural product. This research will be used by scientists developing environmentally safe methods for managing diseases caused by nematodes.

Technical Abstract: Clove oil derived from the plant Syzygium aromaticum is active against various soilborne plant pathogens, and therefore has potential for use as a biobased pesticide. A clove oil formulation previously found to be toxic to the root-knot nematode Meloidogyne incognita in laboratory assays was investigated in greenhouse studies for nematode suppression and phytotoxicity on vegetable crops. Phytotoxicity studies were conducted with 0.1%, 0.2% and 0.3% clove oil applied to soil 0, 2, 5 and 7 days prior to transplant of cucumber, muskmelon, pepper and tomato seedlings. Tomato seedlings were the most sensitive to the clove oil. The 0.2% and 0.3% clove oil treatments applied as drenches at transplant (Day 0) were the most phytotoxic to seedlings of all the tested crop species, with only 0%-50% seedling survival. Most of the clove oil treatments applied as Day 0 drenches decreased shoot heights and fresh shoot weights of all seedlings. Some of the Day 2, 5 and 7 applications of 0.2% and 0.3% clove oil also significantly reduced shoot growth, especially of pepper and tomato. Greenhouse experiments for suppression of M. incognita populations on cucumber were conducted with 0.1%, 0.15% and 0.2% clove oil applied 7 days prior to transplant. Carrier alone, and many clove oil treatments (especially on nematode-inoculated plants), resulted in decreased shoot heights and fresh weights compared to water controls. Roots weighed more on nematode-inoculated plants than on plants without M. incognita. Effects on M. incognita populations were inconsistent between the two trials. In Trial 1, 0.1 and 0.15% clove oil decreased nematode populations compared with carrier controls. In Trial 2, populations were lowest in the water and carrier controls. The results indicate that, under the conditions of these tests, M. incognita populations would not be consistently reduced with clove oil treatments that were not phytotoxic to one or more of the tested vegetable crops.