Allelochemicals Biologica... - Name

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ROBERT J. KREMER
purse (Capsella bursa-pastoris) and burning nettle (Urtica urens) in a California
vegetable production field (Fennimore and Jackson, 2003). The natural soil
suppressiveness of the parasitic weed Striga hermonthica in Nigeria appears to be
related to soils under rotations of cereal and leguminous crops that promote antagonist
microbial populations that destroys Striga seeds before germination or kills the
germinated seedlings (Berner et al., 1996; Dashiel et al., 1991). Each of the above
systems strongly suggests that AB growth can be exploited as a sustainable weed
control strategy using relatively simple management practices.
Tactics and approaches for manipulating the field environment to enhance survival,
physiological behavior, and performance of AB might easily be incorporated into
diverse sustainable crop production systems. Such a strategy for natural weed
suppression, also known as conservation biological control (Newman et al., 1998) or
endemic soil-based control (Kulmatiski et al., 2004) relies on establishment of
populations of indigenous or endemic, weed-suppressive microorganisms in soil. As
demonstrated previously, many of these indigenous microorganisms are AB (Kremer
and Li, 2003; Li and Kremer, 2000). Management practices including tillage, crop
rotation, residue manipulation, and organic amendments enhance or induce favorable
factors in the habitat for sustaining effective populations of natural AB. Crop
management practices that involve reduced tillage, maintain high soil organic matter,
and limit inputs of agrichemicals increased levels of deleterious rhizobacteria associated
with weed seedlings and contribute to natural weed suppression (Li and Kremer,
2000). Deliberate use of management practices that benefit natural weed-antagonistic
AB can adversely affect weed population dynamics in production fields through seed
and seedling mortality and growth suppression.
6. SUMMARY
The future use of AB to manage weeds in both conventional and sustainable agriculture
seems promising. Because AB generally do not attack specific biochemical sites within
the plant, unlike conventional herbicides, they offer a means to control weeds without
causing direct selective pressure on the weed population, therefore, development of
resistance is not a major consideration. Additionally, the use of AB appears to be
environmentally benign relative to herbicides. These characteristics make AB an
attractive approach for managing crop weeds in a sustainable manner, even within
the boundaries of conventional agriculture systems. The recent demonstrations of
apparent weed-suppressive soils may lead to development of specific management
strategies for the establishment and persistence of native AB directly in soils conducive
to annual weed infestations.
7. REFERENCES
Aldrich, R.J., Kremer, R.J. Principles in Weed Management. Iowa State University Press: Ames, IA, 1997
Baker, K.F., Cook, R.J. Biological Control of Plant Pathogens. Freeman: San Francisco, 1974.