Common ragweed (Ambrosia artemisiifolia L., Asteraceae) is an annual herbacious weed that is a troublesome pest in carrot fields of Southwestern Quebec. Over the past decade, ragweed has shown resistance to linuron, the only herbicide that is registered for post-emergence control of this weed in carrots. In this research, the degree of resistance to linuron was investigated for a ragweed biotype collected from a carrot field in Sherrington, Quebec, where a decreased performance of linuron had been noted. This biotype showed a linuron resistance ratio (I50) of 9.09, when compared with ragweed plants collected from a field never sprayed with this herbicide. The fungal pathogen Phoma sp., which had been initially isolated from diseased ragweed leaves in 1993, was considered as a potentially effective biological agent for the control of common ragweed. The pathogenicity of Phoma sp. was re-evaluated during the current research. This fungus was found not to have any appreciable virulence towards common ragweed; it is likely that virulence was lost during storage. Hence, twenty other fungal species were isolated from diseased common ragweed plants and assayed to determine their potential as biological agents against this noxious weed. Varying dew periods, temperatures, spore concentrations, host growth stages, and different types of carrier were evaluated. Only isolates ATT#9, INNA4a, INNA4b, ATT#10, ISO#65, and ISO#68 were able to induce lesions on ragweed foliage at spore concentrations of 106 to 107 spores ml-1, but only after an extended dew period of 48 hrs. No interaction effects on the degree of ragweed control were found when combining five fungal isolates and the insect, Ophraella communa LeSage. However, a possible interactive effect was detected when the fungal isolate ISO#65 and linuron were used in combination.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.33447 |
| Date | January 2000 |
| Creators | St-Louis, Sophie. |
| Contributors | Watson, Alan K. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Plant Science.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001782958, proquestno: MQ70753, Theses scanned by UMI/ProQuest. |
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