Can viable weed control be attainable with microorganisms?

Microorganisms are being exploited for control of weeds using two distinct strategies. The classical approach employs host-limited fungi against exotic, highly aggressive and invasive weeds for which cultural and chemical methods have failed or are inappropriate for economic or environmental reasons. The fungi are highly host specific, coevolved pathogens from the centre of origin of the target weed, and likewise are alien species in the area of introduction. There are some dramatic successes with this strategy demonstrating that this approach is viable, and a truly sustainable weed control method. The second strategy, the inundative or bioherbicide approach, involves the exploitation of indigenous, locally occurring pathogens. These pathogens are normally mass-produced, formulated, and used against the target weed in ways similar to chemical herbicide applications. Research has focused on phytopathogenic fungi, but plant-deleterious rhizobacteria and phytopathogenic bacteria an also being studied as weed biocontrol agents. Many pathogens with bioherbicide potential have been discovered, but few have become commercial realities or viable alternatives. Development has been hampered by biological (weakly virulent), environmental (long dew period requirement), technological (indigent spore production), and commercial (small market size) constraints. Research must shift from discovery to solving production, storage, and efficacy problems that have limited bioherbicide evolvement. Moving away from the "industry partner" technology transfer model to a "farmer or village cooperative" model has specific application for many tropical weed problems.