Dynamics of weed populations : spatial pattern formation and implications for control

J. Wallinga

Research output: Thesisexternal PhD, WU

Abstract

<p>Modelling studies were carried out to analyse spatio-temporal dynamics of annual weed populations and to identify the key factors that determine the long-term herbicide use of weed control programmes. Three different weed control programmes were studied.</p><p>In the first weed control programme, herbicides are applied to the whole field only if the weed density exceeds a threshold value, otherwise there is no control at all. The dynamics of a weed population subjected to such a 'threshold control programme' is characterized by aperiodic (quasi-periodic or chaotic) cycles, whereas the long-term herbicide use does not depend on the threshold value.</p><p>In the second weed control programme, the optimum herbicide dosage is determined and applied to the whole field. In this case the density of the weed population will approach a low equilibrium value. The herbicide use of such an 'optimum dose control programme' is determined by the herbicide dose required to keep the weed population at a low density.</p><p>In the third weed control programme, the spatial scale of weed control decision making is reduced such that only weed patches are sprayed. The herbicide use of such a 'patch control programme' is determined by the spatial pattern of weeds as well as the spatial resolution of the patch sprayer. The patch control programme is only of interest if weeds are heterogeneously distributed over space. It is shown that invading annual weed populations are capable of generating patches, even in an otherwise homogeneous habitat, if the forward tail of the projected seed dispersal curve declines slower than exponential. It is shown that annual weed populations are also capable of generating patches in an otherwise homogeneous habitat if they are held at a constant low density. In the latter case, the weed patch formation is a self-organized critical phenomenon.</p>
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • Kropff, M.J., Promotor, External person
  • Grasman, J., Promotor, External person
  • Lotz, L.A.P., Promotor, External person
Award date11 Dec 1998
Place of PublicationS.l.
Publisher
Print ISBNs9789054859345
Publication statusPublished - 1998

Keywords

  • weeds
  • population dynamics
  • weed control
  • models

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