"The first herbicide we used was 2,-4D which was, of course, useful in a grass crop like corn. Quite effective on broadleaf weeds. Little effect on a grasses… I'm sure it was referred to as a miracle because it's kind of, in comparison to what? We didn't have anything else. So, a farmer could spray 2, 4-D over a growing crop, corn crop that was infested with weeds and selectively – and by that I mean you're going to damage or kill the weeds and minimal effect on the crop. And we didn't have anything that would begin to do that before. We could, of course, cultivate between the rows mechanically. But there was no way to mechanically cultivate right in the cornrow. And of course with the 2, 4-D we could kill the weeds between the rows as well as in the rows. So that introduced a much more powerful tool than anything available before.
     "Why does 2, 4-D kill a broad-leaf plant and not a grass plant? Well, broad-leaf plants tend to have their growing points – the point where cells divide and enlarge – out at the tips of the plant. So that when you treat, the 2, 4-D is going to come in very close contact with the growing point. And 2, 4-D is a so-called growth regulator herbicide. It upsets the normal process of cell division and enlargement. For it to be effective it needs to get to the growing point.
     "[In] grass plants, in contrast, the growing point is not out at the leaf tip. For example, the growing point of a corn plant – or, since we're talking about grass as weeds, a foxtail plant that's three inches tall – the growing point is down right at the soil surface in the crown. So if you spray over the top of the foxtail, the 2, 4-D does not come in close contact with the growing point. So getting the 2, 4-D close to the site of action was one aspect because structurally the growing point is out on the tips of stems on a broad-leaf. And also, movement of the herbicide in the plant is much restricted in the grass plant. So you spray the end of the grass leaf and it doesn't move to the growing point, which is at the base, whereas 2, 4-D does move or translocate readily in broad-leaf plants. So, you could spray a leaf tip and it would move back to the growing part where there's cell division. So, the difference is in the location of the dividing cells, movement or translocation patterns are primarily responsible for the difference in sensitivity…
     "The plant, for lack of a better description, embarks on uncontrolled growth and some tissues grow very rapidly and others don't grow at all. And so if you watch and observe a plant over five or six days after it's been treated, it'll twist and bend. If the outside of a stem grows faster than the other side it'll curve. Well, the plants curve and twist and turn. And that disrupts the vascular tissue – for lack of a better term the plumbing in the plant. It disrupts the transportation equipment in the plant for moving fluids and food. So the plant – A common term used is the plant grows itself to death. Now that may not be technically true, but it's sort of unregulated or misguided growth that results in the destruction of vital tissues."

Alex Martin – How 2,4-D Works


Other Excerpts from Alex Martin’s Interview:

Cold War Air Raid Drills
The Green Revolution
The DNA Revolution
Symbiosis of Technologies
The Weed Challenge
Silent Spring
How Atrazine Works
Futures Markets