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