Vol. 54—2000 - NorthEastern Weed Science Society

CONTROLLING ASTERACEAE WEEDS WITH REPEAT APPLICATIONS OF
PSEUDOMONAS SYRINGAE PV TAGETIS AND SILWET L-77.
J. C. Porler, T. A. Bewick, F. L. Caruso, and D. Henderson'
ABSTRACT
Single applications of bacterial suspensions of Pseudomonas syringae pv tagetis
(Pst) (10E9 cfu/ml) plus Silwet L-77 (0.5% vlv) to the Asteraceae weeds narrowleaf
goldenrod (Euthamia tenuiifolia), dandelion (Taraxacum officinale), and devil's
beggarticks (Bidens frondosa) at the 4 to 6 leaf stage have resulted in limited reductions
in biomass production by the plants for the first 2 to 3 weeks following treatment. By the
fourth week after treatment, plants recover from the disease and resume normal growth.
In greenhouse studies, repeat applications of bacterial suspensions of Pst (10E9 cfu/ml)
plus Silwet L-77 (0.5% v/v), were applied one, two, and one and two weeks after the
initial applications to the same weeds, 5 mVplant, 4 replications per treatment. Shoots
were harvested five weeks after the initial applications were made and their dry weight
determined. All repeat applications significantly increased the amount of control
achieved (up to 100% control of dandelion, 95% control of narrowleaf goldenrod, and
57% control of devil's beggarticks). There were no significant differences among them.
1 DoctoralCandidate,ExtensionProfessor,ExtensionAssistantProfessor,and
Research Assistant, University of Massachusetts Cranberry Experiment Station,
East Wareham, MA 02538
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