While weed populations have traditionally been controlled by chemical
and cultural methods, inundative biological control with microbial age
nts offers an additional strategy for managing weeds. Foliar pathogens
have long been sought after as potential biocontrol agents, but rhizo
sphere microorganisms and their influence on weed growth and developme
nt have been ignored until recently. Rhizosphere soil is replete with
a variety of microorganisms such as rhizobacteria, pathogenic soil-bor
ne fungi, and arbuscular mycorrhizal fungi, all of which have a direct
or indirect impact on weeds and their competitive ability. In some ca
ses, specific microbes have a detrimental effect on the weeds and can
be exploited as biological control agents. The ubiquitous mycorrhizal
fungi are beneficial symbionts that can impart a competitive advantage
to their plant hosts, particularly if mycorrhizal dependency is exhib
ited in weeds as opposed to crops. It may be possible to exploit vario
us soil microbes by directly or indirectly reducing weed competition a
nd tipping the competitive advantage in favor of the crop. However, in
formation available on microbial/weed/crop relationships is limited an
d research efforts are required to explore the use of soil microorgani
sms as another weed management tool.