Allelochemicals Biologica... - Name

ALLELOPATHIC BACTERIA IN WEED MANAGEMENT 149
in leafy spurge-infested sites in South Dakota suppressed growth by decreasing root
weight and root carbohydrate content (Brinkman et al., 1999).
Most of the weeds targeted for biocontrol by AB infest cereal and row crops, but
a few are perennial weeds of rangeland and forest ecosystems (Kremer, 2002). Selected
AB are intended for soil application, however, some cultures might be effective when
applied directly to growing weeds in a postemergence control strategy. Selected AB
might also be applied directly to growing weeds as a postemergence control strategy.
For example, cultures and cell-free supernatants of AB strains sprayed on common
chickweed (Stellaria media), common lambsquarters (Chenopodium album), and field
pennycress (Thlaspi arvense) in the greenhouse and field reduced plant biomass and
survival (Weissmann and Gerhardson, 2001). Preliminary results suggest AB cultures
might be used for selective weed control in growing crops through a one-time foliar
application or as a follow-up to soil-incorporation of the same cultures.
5.2. Integrated Weed Management
Integrated weed management systems rely on a number of available strategies including
tillage, cultural practices, herbicides, allelopathy, and biological control to reduce the
weed seedbank, prevent weed emergence, and minimize competition from weeds
growing with the crop (Aldrich and Kremer, 1997). These systems may be most suitable
for implementing bioherbicides based on AB to counteract their limited weed host
specificity. Like chemical herbicides, such bioherbicides may be most effective as a
component in a multi-faceted management program rather than as a single tactic
approach (Hatcher and Melander, 2003). Effective weed management offers several
opportunities for integration of selected AB at the critical stages of weed development:
as seeds in soil, as growing and competitive plants, and during seed production (Aldrich
and Kremer, 1997). This may be the most promising situation for AB to be considered
as practical management options in cropping systems.
To broaden the limited spectrum of activity of AB, several tactics have been
proposed for integration of these organisms with other weed management methods.
Weed growth suppression by AB combined with herbicides applied at sublethal rates
has met with some success (Greaves and Sargent, 1986). AB inhibitory to downy
brome and jointed goatgrass suppressed growth to a greater extent when combined
with metribuzin and/or diclofop at less than label rates (Kremer and Kennedy, 1996).
An understanding of the mechanisms of herbicide-AB interactions will lead to
strategies where AB selected for activity toward a weed can be paired with a specific
chemical that increases the susceptibility of that weed to the AB (Kremer, 1998). Use
of AB in this manner may develop into a systems management approach that involves
integration of bioherbicides and herbicides on a physiological basis to control
economically important weeds in corn and other crops. This is currently under intensive
evaluation as a potential integrated management system in Europe (Müller-Schärer
et al., 2000). Successful development of these integrated strategies will increase efficacy
of AB agents, reduce herbicide inputs for weed control, and decrease potential
environmental contamination.