Week Management

Week Management

1. Biological control

   • Definition = the action of parasites, predators or pathogens to maintain another organism’s population at a lower average than would occur naturally in their absence.
   • Target = reduction and long-term stabilisation of weed density to non-injurious levels
   • Difficulties
     • Host specificity
     • Dynamic - level of control achieved
     • Persistence of agent

2. Chemical control

   • Herbicide = ‘A chemical that disrupts the physiology of a plant over a long period to kill it or severely reduce its growth’
   • Types of chemicals
     • Non-selective
     • Selective
     • Contact
     • Systematic
   • Types of application
     • Pre-sowing
     • Pre-emergence
     • Post-emergence

3. Herbicide resistance

   • Herbicide resistance naturally exists (and/or spontaneously evolves) at very low levels in the overall weed population
   • Reliance on repeated use of herbicides alone selects resistant weeds
   • Spread
     • Pollen flow
     • Seed dispersal
     • Human Dispersal
   • Management
     • Mixtures or sequences of herbicides with differing modes of action (but beware cross-resistance)
     • Crop rotations
   • Mechanisms
     • Target Site resistance
       • "resistant" gene produces altered enzyme
       • reduced (or even lost) ability of the herbicide to bind to its target protein
     • Non-Target site resistance
       • Reduced leaf absorption
       • Altered translocation (including sequestration or exclusion)
       • Herbicide metabolism
       • Limitation of oxidative damage
       • educe the amount of herbicidal active compound reaching the target site
     • Metabolic Resistance
       • A resistant metabolism slows the uptake of herbicide to the point of no weed control

4. Cultural control

   • Rotation
     • Definition = rotating in different crops throughout the year minimise weed population
   • Cultivating
     • Burial = burying weeds under the soil
     • Cutting = severance of the aerial parts from the roots or rhizomes
     • Stimulation = the provision of a soil environment that encourages dormant seeds or buds to change into an active and therefore vulnerable state
     • Desiccation = rhizomes or roots are brought to the soil surface where they may be exposed to a dry atmosphere or dry soil
     • Exhaustion = the continues stimulation of dormant buds on perennial weeds
     • Crop competition
       • Promote competition in favour of crop, rather than weed
       • Competitive plant could be beneficial to the crop (layer of clover that fixes N and limits weeds)
       • Does NOT kill weed but reduces seed production and reduces crop yield loss

5. Future Control

   • More herbicides
   • Robots
   • Integrate multiple control methods
   • Site-specific management
   • RNAi

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