1 January 2006 Field-based evaluation of a novel approach for infecting Canada thistle (Cirsium arvense) with Pseudomonas syringae pv. tagetis
Ryan P. Tichich, Jerry D. Doll
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Canada thistle is resilient to many control tactics, especially in undisturbed sites. Such sites are suitable for slow acting biological control agents, such as the bacterium Pseudomonas syringae pv. tagetis (PST), because complete control is usually not required in the short term. A new method of introducing or intensifying PST infection of Canada thistle was investigated. Sap of naturally infected Canada thistle was extracted and applied in water plus Silwet L-77 organosilicone surfactant with a backpack sprayer to healthy Canada thistle plants in the field. Application variables of time of the season, spray volume, concentration, and frequency were studied. When practical field rates were applied, infected sap concentration and spray volume did not affect the level of disease observed. This suggests that PST applications could be practical at the field scale because a single application caused apical chlorosis. However, multiple applications proved beneficial because four consecutive weekly applications caused greater disease incidence (50%) than one or two applications (28% and 30%, respectively). Disease symptomology was greatest when PST was applied in mid-July rather than mid-June or mid-August. However, the levels of disease expression were not adequate to effectively suppress Canada thistle. Increased toxin production, either by finding ways to support higher PST populations or by selecting strains that produce more toxin per bacterial cell, would improve this system.

Nomenclature: Canada thistle, Cirsium arvense (L.) Scop., CIRAR.

Ryan P. Tichich and Jerry D. Doll "Field-based evaluation of a novel approach for infecting Canada thistle (Cirsium arvense) with Pseudomonas syringae pv. tagetis," Weed Science 54(1), 166-171, (1 January 2006). https://doi.org/10.1614/WS-03-144R3.1
Received: 27 October 2003; Accepted: 1 September 2005; Published: 1 January 2006
organosilicone surfactant
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