Weed & herbicide considerations in conservation agriculture

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  • 1. 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)
  • 2. 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.
  • 3. Soil Facts – Saskatchewan soil conservation association 2001
  • 4. 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
  • 5.
  • 6. 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
  • 7. 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
  • 8. 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