Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/1999
Publication Date: N/A
Interpretive Summary: Field trials were conducted in South Dakota to assess the effects of deleterious rhizobacteria on growth of the noxious and invasive rangeland weed, leafy spurge. Leafy spurge infests large acreages of land, is unpalatable to cattle, and is very difficult and expensive to control with chemical herbicides. Deleterious rhizobacteria are a group of bacteria that live on roots of plants and, when they are the major group in the roo zone, can adversely affect the growth of their host plant. Thus, these bacteria are attractive for biological weed control since weeds might be suppressed with little or no use of herbicides, which could damage native plants and harm water quality. The deleterious rhizobacteria used in this study originated from leafy spurge roots, were grown in large quantities in the laboratory, and applied in a granular form around leafy spurge plants infesting prairie sites. Plants treated with the rhizobacteria collected over a two-year period had fewer buds at the base of stems and lower carbohydrates in the roots. These results are important to scientists and producers because results show that a new biocontrol agent, the rhizobacteria, may soon be available for use as another alternative strategy for integration with insects, fungal pathogens, mowing or grazing to further augment reductions in leafy spurge infestation through biologically-based management.
Technical Abstract: Strains of rhizobacteria are phytotoxic to leafy spurge in laboratory screenings. This field study investigated the influence of deleterious rhizobacteria (DRB) (Pseudomonas fluorescens) on leafy spurge (Euphorbia esula L.) root weight, bud number, and root carbohydrates at three field sites in South Dakota in 1995 and 1996. Soils were inoculated with starch-base granules containing either no DRB (controls) or containing 100 million cells per g of DRB isolate LS102 (Montana origin) or isolate LS174 (South Dakota origin). Both isolates were detected on roots taken from all treatment areas during both sampling years. Deleterious rhizobacteria reduced root weight and root carbohydrate by about 20% compared to roots of plants receiving blank inocula. Depletion of root energy reserves by DRB may decrease vigor and survival and increase the effectiveness of other approaches used controlling leafy spurge.