Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 24, 2006
Publication Date: March 8, 2007
Citation: Boyette, C.D., Hoagland, R.E., Abbas, H.K. Evaluation of the bioherbicide Myrothecium verrucaria for weed control in tomato (Lycopersicon esculentum). Biocontrol Science and Technology 17:171-178. 2007. Interpretive Summary: Weed control in tomatoes, of species such as Portulaca (common purlane and horse purslane) and Euphorbia (the spurges, spotted and ground spurge) is a serious limitation to production in the Southeastern U.S. An isolate of the fungal pathogen Myrothecium verrucaria can act as a bioherbicide to control these weeds in greenhouse and in field tests without detrimental effects to tomato plants. The fungus applied alone postemergence provides no control of these weeds, but when formulated with a surfactant (Silwet L-77), 80 ' 95 % mortality of the weeds was achieved. The bioherbicide provided weed control for these purlane species equal to that obtained for the synthetic herbicide metrbuzin, but was about 10 % lower than metribuzin control of these spurges. These overall results indicate that, when formulated with surfactant, Myrothecium verrucaria can be an effective bioherbicide for controlling purslanes and spurges in tomatoes, and may have utility in organic farming production systems.
Technical Abstract: An isolate of the fungus Myrothecium verrucaria (MV) was evaluated for its biocontrol potential against common purslane (Portulaca oleracea), horse purslane (P. portulacastrum), spotted spurge (Euphorbia maculata), and ground spurge (E. prostrata), all serious weed pests in commercial tomato (Lycopersicon esculentum) fields in the Southeastern U.S. In both greenhouse and field tests, the bioherbicide MV was highly virulent against these weeds when applied as conidial sprays formulated in 0.2% Silwet L-77 surfactant (SW), even in the absence of dew. In field test plots naturally infested with these weeds, seedlings in the 2-to-3 leaf growth stage treated with MV at 1 x 107 conidia mL -1 in 0.2% SW, exhibited leaf and stem necrosis within 24 h following inoculation, with mortality occurring within 96 h. After 7 days, MV had killed 90-95% of both purslane species and 85-95% of both spurges. Tomatoes that were transplanted into plots treated with MV remained healthy and vigorous throughout the growing season. Since MV effectively controlled several common weeds under field conditions, this fungus appears to have potential as an effective bioherbicide for pre-plant weed control in production systems with transplanted tomato.