An interesting study was done by the University of Washington College of Forest Resources back in the mid 1970s, funded by Monsanto or one of the other chemical giants. During reforestation of recently logged areas, rounds of cardboard impregnated with various strengths of 2,4-d (I believe a primary ingredient in today's Roundup) were placed around newly planted seedlings. After some amount of time (perhaps 3-5 years?), the seedlings were measured to see if there was a significant difference between the groups. The bottom line was the control group (non treated cardboard) was just as effective as the cardboard with the highest dose of 2,4-d. Obviously, this was not the hoped-for result, but I did get a bit of laugh out of it much to the dismay of the graduate students working on the project. (I was the Forestry administrative secretary at the time, so responsible for preparing/distributing research reports.)
I actually tried to locate this old research online, but back then I was using a memory typewriter and computers were giant behemoths housed in separate rooms and fed with those stacks of punched data cards, so who knows where the info might be today...
Just a little blast from the past, but it definitely influenced my gardening habits - to this day, I just give new shrubs/trees a good solid cardboard ring when I first plant them, often topped with a layer of wood chips or compost mix to make it a bit more visually appealing. Rather like lasagna gardening I suppose.
