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How do pre em herbicides work?
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<blockquote data-quote="ollie989898" data-source="post: 8160412" data-attributes="member: 54866"><p>If you have weeds germinating from depth, they will be too strong or remain unaffected when they reach the layer of chemical in the soil. PDM is notorious for this. It's not so much dry soil conditions that are to blame, it's the depth from which weeds are emerging.</p><p></p><p>This is the biggest issue with minimum tillage- things like solos, sumos and topdowns with discs and tines mix huge volumes of soil in a kind of boiling action. This means seeds that have fallen out of the combine or out of the ear beforehand are mixed thoroughly throughout the soil profile. Ploughing, if done correctly, inverts the soil in one action and does not give this same mixing action. You can see this in the differences in levels of volunteers where min-till and ploughing are used.</p><p></p><p>It is possible that some farms have full blown resistance (probably enhanced metabolism) against some or even all soil acting herbicides however. The fact remains that many of these products cannot kill many established plants at any rate or in any conditions no matter how favourable. The point at which they are most effective is when the tiny white coleoptile (and first seminal root) is emerging from the seed. They absorb a dose of the chemical and cell division is disrupted meaning very poor or zero growth from that point on.</p><p></p><p>Unfortunately, trifluralin, flufenacet and pendimethalin all share this same kind of mode of action. From memory only IPU was a genuine photosystem inhibitor which made it a bit more effective even on established plants.</p></blockquote><p></p>
[QUOTE="ollie989898, post: 8160412, member: 54866"] If you have weeds germinating from depth, they will be too strong or remain unaffected when they reach the layer of chemical in the soil. PDM is notorious for this. It's not so much dry soil conditions that are to blame, it's the depth from which weeds are emerging. This is the biggest issue with minimum tillage- things like solos, sumos and topdowns with discs and tines mix huge volumes of soil in a kind of boiling action. This means seeds that have fallen out of the combine or out of the ear beforehand are mixed thoroughly throughout the soil profile. Ploughing, if done correctly, inverts the soil in one action and does not give this same mixing action. You can see this in the differences in levels of volunteers where min-till and ploughing are used. It is possible that some farms have full blown resistance (probably enhanced metabolism) against some or even all soil acting herbicides however. The fact remains that many of these products cannot kill many established plants at any rate or in any conditions no matter how favourable. The point at which they are most effective is when the tiny white coleoptile (and first seminal root) is emerging from the seed. They absorb a dose of the chemical and cell division is disrupted meaning very poor or zero growth from that point on. Unfortunately, trifluralin, flufenacet and pendimethalin all share this same kind of mode of action. From memory only IPU was a genuine photosystem inhibitor which made it a bit more effective even on established plants. [/QUOTE]
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How do pre em herbicides work?
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