On the development, environmental effects and human dimension of weed management strategies

Research output: Thesisexternal PhD, WU

Abstract

On the development, environmental effects and human dimension of weed management strategies.
On farm weed management is influenced by many factors. These factors comprise the development and availability of weed management tools, the environmental impact of these tools and the attitude and behaviour of the farmer. In this research major gaps in our knowledge on each of these aspects were identified. Research questions were formulated concerning ecological weed management strategies depleting the soil seed bank, environmental effects of chemical weed management and the human dimension of weed management.
Two ecological weed management strategies were investigated regarding the reduction of the soil seed bank. The principle of the first strategy was to stimulate the germination and emergence of weed seeds within a growing season. The principle of the second strategy was to reduce the seed return to the soil seed bank within a crop rotation. To test the applicability of the first strategy several stale seedbed treatments in combination with mechanical weed control techniques were applied. Similar levels of annual weed control during crop growth were achieved as with chemical control. To test the applicability of the second strategy three different levels of seed return to the soil seed bank were allowed: one level aimed at a 100% prevention of seed return, one level at the prevention of seed return from the largest plants (thus, the plants with most seeds), and a reference level, representing standard weed control in an organic system. The strategies were applied for a period of seven years and their effects on the aboveground weed density and the soil seed bank were monitored at the end of this period. The weed densities in plots aiming at a 100% prevention of seed return became significantly lower than the weed densities in plots allowing for the other weed seed return levels. Both strategies targeting the soil seed bank proved to be useful strategies to reduce weed densities during crop growth.
Research questions on environmental effects of chemical control focused on the risk assessment of herbicides to terrestrial non target plants. The influence of plant development stage and surrounding vegetation on the plant sensitivity to herbicides, the influence of the choice of end point and the use of greenhouse data for assessment of effects in the field were investigated for small and broad spectrum herbicides. Effects on the biomass of greenhouse and field-grown plants were found to be related at different effect levels, indicating that it might be possible to translate results from greenhouse studies to field situations. The relationship between greenhouse and field effects is probably herbicide specific and should be assessed for each group of herbicides with a similar mode of action. The response of a single plant species to sublethal herbicide dosages differed to the response of the same species grown in a mixture with other species. The results also suggest consequences at the population level. Even when only marginal effects on the biomass of non-target plants are expected, their seed production and thereby survival at the population level may be negatively affected.
The third part of the thesis investigated the human dimension of weed management. Most studies on weed population dynamics in farming systems have focused on the effects of different farming systems. Those studies usually assume that farmers, operating within a particular system, show homogeneous management behaviour. However, it is likely that weed management behaviour will vary between farms that operate within one system, thereby influencing the weed pressure. The farmer’s beliefs and knowledge on weed control techniques differed between farmers with different weed pressures.
It was concluded that future sustainable weed management strategies with a minimum environmental impact would benefit from an approach combining social and natural sciences.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Kropff, Martin, Promotor
  • Lotz, Bert, Co-promotor
Award date7 Dec 2009
Place of Publication[S.l.
Print ISBNs9789085856696
Publication statusPublished - 7 Dec 2009

Keywords

  • weed control
  • weeds
  • seed banks
  • environmental impact
  • manual weed control
  • behaviour

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