Controlling Weeds with Phytopathogenic Bacteria

Abstract

Until recently, phytopathogenic bacteria have not been considered potential biological weed control candidates because they lack the ability to penetrate intact plants. This deficiency can be overcome by providing entry wounds or using surfactants. Spray application ofPseudomonas syringaepv.tagetis(5 × 108cells/ml) in aqueous buffer with a surfactant produced severe disease in Canada thistle, common ragweed, Jerusalem artichoke, sunflower, and certain other members of the Compositae under field conditions. Spray application of the bacterium without surfactant was ineffective on all reported hosts.Xanthomonas campestrispv.poannuacontrolled annual bluegrass in bermudagrass golf greens when applied by spray during mowing. The bacterium entered through mowing injuries, causing lethal, systemic wilt. Application of the bacterium to annual bluegrass in the absence of fresh mowing injuries failed to produce symptoms. Under field conditions, this previously unknown pathovar's host range was limited to a single subspecies of annual bluegrass, but inundative application to freshly mowed turf resulted in infection of diverse annual bluegrass biotypes. In field trials, six monthly applications resulted in greater than 70% control. The preceding examples are among the first attempts to use foliar phytopathogenic bacteria for biological weed control. Efficacy of these bacterial bioherbicides and of future biocontrol strategies employing bacteria is dependent on facilitated host penetration.

Bioherbicides in Organic Horticulture

“…Pathogenic bacteria Xanthomonas campestris pv poannua and P. syringae pv tagetis have been developed as bioherbicides to control annual bluegrass (Poa annua) and Asteraceae weeds, respectively [25]. The phytotoxin produced from a crude extract of Pseudomonas syringae reduced root and shoot growth of weeds in newly-established "Stevens" cranberry bogs [26].…”

“…Chandramohan and Charudattan (2003) [76] also found that a mixture of three pathogens, Drechslera gigantia, Exserohilum longirostratum, and Exserohilum rostratum, successfully suppressed the growth of seven weeds in citrus groves in Florida. Amendment of bacterial pathogen aqueous suspensions with surfactants has been studied for helping bacteria efficiently invade plant leaves and broaden host range [25]. Types of formulations using emulsions, organosilicone surfactants, and hydrophilic polymers have advantages and disadvantages in enhancing the efficacy of biotic agents and ease of application [69].…”

Bioherbicides: Research and Risks

“…A Pseudomonas syringae isolate has been registered to control Canada thistle (Johnson et al, 1996). Other Pseudomonas syringae phytotoxins include: coronatine, syringomycin, syringopeptin, tabtoxin, phaseolotoxin, and tagetetoxin (Table 6).…”

Innovative Applications of Microbial Agents for Biological Weed Control

“…poannua was shown to control annual bluegrass (Poa annua L.) in bermudagrass ( Table-2) (Johnson, 1994;Johnson et al, 1996). The bacterial agent causes systemic wilting, yellowing and death of the grass and the host-range of this pathovar is restricted to P. annua ssp.…”

“…tagetis is being pursued as a possible bioherbicide for Canada thistle (Cirsium arvense L.) control in soybean (Table 2) (Johnson et al, 1995). The bacterium was first reported on marigold, sunflower, common ragweed, and Jerusalem bacterium was first reported on marigold, sunflower, common ragweed, and Jerusalem artichoke and causes apical chlorosis of Canada thistle (Johnson and Wyse, 1991;Johnson et al, 1996). Application of the bacterium in the spring reduced the number of Canada thistle stems/m 2 by 78%, compared to the controls, and no disease occurred on soybean.…”