Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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AN OUNCE OF PREVENTION. M.J. VanGessel, Univ. of Delaware, Georgetown, D.
Doohan, Ohio State Univ., Wooster, P.J. Christoffoleti, S.J.P. de Carvalho, and M.
Nicolai, Univ. of São Paulo, Piracicaba, São Paulo, Brazil.
ABSTRACT
Prevention has been a cornerstone of weed management throughout history and
arguably is the most cost-effective approach that a grower can take. However,
preventive management is complex, involving integration of a group of practices and
policies that avoids introduction, infestation, or dispersion of certain weed species to
areas free of those species or biotypes. At the agro-ecosystem level, seed or propagule
dispersion from field to field and from farm to farm needs to be recognized as an
important factor that affects the whole agricultural system and should be included in
comprehensive weed management planning.
In the absence of human activity weeds rely upon the same natural processes for
dissemination as do other plants; dispersal by wind and water, adhesion to fur or
feathers, and through food webs. However, farming, trade, and human migration
usually amplify the impact of these dispersal adaptations.
Dispersal of weeds by human activities include plant introductions, use of
infested crop seeds, movement with machinery and equipment, movement with
harvested plant parts, movement with soil, animals and associated manure, and use of
infested irrigation water. Manure application, irrigation water, use of plant material as
organic matter (although not quantified in the literature), and use of weed seed
contaminated crop seed all contributed thousands to hundred of thousands of seeds per
hectare. Additional management practices (i.e., composting, addition of screens, etc.)
can have dramatic impacts on reducing the number of viable seeds; however, seldom is
the loss of viability 100%.
The focus of a prevention program is two-fold, to eliminate the introduction of
new species (or biotype) as well as reducing the number of seeds in the weed seed
bank. Once a species is introduced and is allowed to emerge, become established, and
produce seed, there is potential to become a significant portion of the weed seed bank
in a relatively short period.
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