Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/1998
Publication Date: N/A
Interpretive Summary: Cocaine is a narcotic produced from the leaves of the coca plant and is grown in various South American countries. Bioherbicides offer an environmentally safe alternative to standard coca control methods in the tropical regions where coca is grown. The selective plant pathogen, isolate EN-4 (F. oxysporum f. sp. erythroxyli), is being evaluated as a bioherbicide for control of coca. The bioherbicidal formulations effectively killed coca plants in two of three field tests. Coca plants began dying 4-7 months after treatment. We have developed a bioherbicide which potentially can be used to control coca production. The damage to society by misuse of the coca plant is extensive. Both producing and consuming nations suffer cocaine's ill effects. The bioherbicidal formulations described in this manuscript, if used, could contribute greatly to the reduction in cocaine production and result in reduced costs to society.
Technical Abstract: Formulations of F. oxysporum Schlechtend:Fr. f. sp. erythroxyli, isolate EN-4, pathogenic to Erythroxylum coca var. coca (coca) were evaluated in greenhouse and field studies to determine their relative ability to enhance pathogen populations in the soil and/or cause disease in coca. The formulations were applied in the greenhouse and field at 33.6 kg ha**-1. All the formulations tested enhanced the population of EN-4 in the soil during greenhouse (>7 weeks) and/or field (>7 months) experiments. En-4 was present in the upper 1 cm of formulation-treated soil at 10-fold higher levels than populations established throughout the top 7 to 10 cm depth in both greenhouse and field experiments. The formulated F. oxysporum began to have a significant effect on plant death 100 to 200 days after application in 2 of 3 field experiments, based on repeated measures analysis. The various formulations tested tended to establish similar pathogen populations when applied at the 33.6 kg ha**-1 rate and subsequently cause similar levels of disease. The population of EN-4 established was approximately 5-fold lower in the field experiment in which the disease rate was not influenced by formulation compared to a similar test where disease rate was influenced. The reduced pathogen population was associated with root colonization and reduced kill. The data suggest that formulations starting with the same biomass and with a similar potential for producing and establishing high pathogen populations in the soil may be expected to cause a similar rate of disease development. The primary factors influencing formulation performance may be environmental, since inoculum production is dependent upon sporulation of the formulation which, although rapid, may continue over several weeks subsequent to application.