Weed & herbicide considerations in conservation agriculture
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Weed & herbicide considerations in conservation agriculture

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    Weed & herbicide considerations in conservation agriculture Weed & herbicide considerations in conservation agriculture Presentation Transcript

    • Weed and Herbicide Considerations
      Tillage and weed germinationResidue effect on weeds
      Herbicide in no till
      Guidelines for pre emergent herbicide
      Jack McHugh
      Jeff Esdaile
      Contributions from Dr Jack Desbiolles (Ashworth et al., 2010) and Baker et al., (2007)
    • Tillage and weed germination
      Germination affected by:
      Tillage, Climate & Soil type
      Tillage effects microenvironment;
      Light, O2,CO2 diffusion, Temp, N and Soil structure
      – breaks down dormancy and stimulates germination.
      Low soil disturbance disc seeding systems = a shallow weed seed bank – affected by herbicides, low germination rates & predation
      Deep seed bank - long term seed viability, weed reinfestation if brought to the surface.
    • Soil Facts – Saskatchewan soil conservation association 2001
    • Residue effect on weeds
      Crop residue retention influences weed germination – temperature, moisture, chemical interactions.
      Affects growth of bothcrop and weeds – soil to seed contact, N tie up, reduced soil temp, increased root diseases, release of phytotoxins
      Effect on weed emergence is complex:
      Type and quantity of residue
      Allelopathy
      Weed species
      Seed depth
      Soil type
      Environmental conditions
      Interaction with herbicides
      The efficacy or pre emergent herbicides improves under higher disturbance disc seeding systems due to increased incorporation
    • Herbicide in no till
      Pre-emergent herbicides were introduced to combat resistance in post emergence herbicides.
      Trifluralin (treflan) is incorporated (photodecompostion) by soil throw near the surface. Other chemicals can be toxic to crop seeds at high rates
    • Herbicide in no till
      Furrow free of herbicide – treated soil is thrown and mixed between furrows
      Minimum disturbance, minimises mixing of soil and weeds to depth - Small amount of soil throw.
      Efficacy controlled by positional selectivity – seed & herbicide separation
      Performance is a function of amount and pattern of soil throw
      Leading fluted coulters are effective (dbl discs drag herbicide into furrow)
      Triple discs appear to perform the best (speed and layout is a factor)
      Hair pinning a significant issue + soft wet clay
    • Guidelines for pre emergent herbicide
      Pre plant knockdown – emerging weeds
      Optimise application rates – with separation 1.5-2 L/ha in cultivation systems 0.8L/ha = less effective
      Travel speed – Disturbance and throw affected by speed, depth, soil texture and moisture – avoid throw to adjacent seeding rows – monitor closely
      Stubble – herbicide efficacy reduced by 40-50% if not on the soil
      IWM – integrated weed management reduces weed burden and limits evolution of resistance