Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 2/10/2002
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Growth chamber and field experiments were conducted to assess the potential of Pseudomonas syringae pv. tagetis (Pst) as a biocontrol agent for Canada thistle (Cirsium arvense). Silwet L-77, an organosilicone surfactant, was required to facilitate Pst penetration into Canada thistle leaves. Growth chamber experiments indicated that maximum Pst populations inside leaves were obtained with a Silwet L-77 concentration of 0.3% (v/v) or greater. High Pst populations [109 colony forming units (cfu) per g fresh wt] were found in leaves 48 h after treatment with 108 or 109 cfu mL-1 Pst plus Silwet L-77 (0.3%, v/v). In growth chamber experiments, foliar application of Pst (109 cfu mL-1) plus Silwet L-77 (0.3%, v/v) to 4 to 5 wk old Canada thistle reduced shoot dry weight by 59% (measured 14 d after treatment) and chlorophyll content of emerging leaves by 95% (measured 10 d after treatment). In field trials conducted in 1999 and 2000, Pst (109 cfu mL-1) plus Silwet L-77 (0.3%, v/v) were applied at 700 L ha-1 and the method of application (paint gun, backpack sprayer, boom) and number of applications (1 or 2 separated by 14 d) were examined. Averaged over 2 yr, two applications with a backpack sprayer resulted in: (a) 67% disease incidence (apical chlorosis) of treated plants measured at 4 wk after the initial treatment, but little or no disease incidence at the time of flower bud formation; (b) 31% reduction in plant height; (c) 81% reduction in number of flower buds; and (d) 20% reduction in shoot survival during 1999, but no effect on survival in 2000.