Cultural management determines weed populations
An edited excerpt from the podcast interview with Klaas Martens:
The first year after you abandon a field that’s been in real crops—let’s say it’s been a corn field—think about what weeds will grow. Obviously there’ll be lambs quarter, pigweed, foxtail, velvetleaf, the whole range. They’re mostly seeds of weeds that make huge numbers of seeds. You may end up with millions of seeds per square foot on the field. But what grows the second year? Now from our reductionist way of thinking, we would assume that because we just made that many seeds, we should have a lot bigger problem with those weeds. But the second year, none of those plants are growing. We have other weeds growing there. And if you take that forward several more years, you start seeing goldenrod, woody plants, brambles, sumac—you know, all the thorny stuff and all the multiflora rose. And if you take it forward a few more years, you’re going back to forest.
This is something Dr. Albrecht wrote about. If you let it go for five hundred years, at least where we are, it would be back to old-growth hardwood forest—mostly oak—which Dr. Albrecht called the climax crop. That’s the kind of a steady state that nature would put the land in. This is how the land was made to work: it creates this succession where all of the species and communities—each one—changed the soil. And the reason all of those weeds that set seed didn’t grow the second year was that the plants that made them changed the soil, and that the right conditions weren’t there for those plants to grow the next year. So other plants grew. And that group, again, changed the soil, so that another group grew.
Now thinking back to what Dr. Albrecht wrote—he talked about these successions as actually being more productive, more diverse, and more vibrant than the climax crops. So that the tallgrass prairie and the oak would have been very stable, very resistant to invasions and diseases. Those plants didn’t get sick—they could tolerate flood, storms, whatever, and remain in very healthy condition. Albrecht used to tell his students to see what they were looking at—to see how nature does its crop rotation.
I started looking at a pest that forced me to start asking why it was there and what exactly it was doing in the soil. Take this back to the succession that we observe. Obviously, these plants are changing the soil, and left to their own devices, they kind of work themselves out of a job and something else grows. I had to look at everything that I could observe. I had to try to see everything there was to see—look at it through new eyes—look at it through something that is working exactly as it was intended to.
And the problem was me. If I didn’t like something, I had to own it and say, “This is the result of what I’ve done up till now. Now, how do I change that?” More importantly, how do I learn from it? So I started to study what these different weeds and pests do in the soil. And that grew into a system of how to read what the soil is saying and how to understand the language that the fields are using to try to teach us.
There was a weed that at one point I thought was going to make it impossible for us to farm organically. I was really frustrated. It seemed like this velvetleaf grew taller than the corn, no matter how carefully I cultivated—a lot of it always survived. I had a one-acre spot in particular where I ended up mowing it. The corn wasn’t going to be a crop—there was nothing developing. After about three or four years, it wasn’t quite as bad, and the area where the crop didn’t amount to much was smaller. Fast forward another three or four years, and lo and behold—my velvetleaf was getting into mid-summer and then it was starting to turn yellow. The lower leaves were turning brown, the lowest leaves had fallen off, and before the end of the summer it was dead. And not only that, but instead of being taller than the corn it was only about three to four feet tall.
So I called a friend at Cornell who is a lead ecologist. And I was still thinking completely wrong. I told him I had found a disease that was going to make me a millionaire. My brilliant idea was that we could catch those spores and make a product out of them. And my friend came out and looked the situation over. He said, “I’m familiar with these leaves, and you can go ahead with your plan. But before it can be successful, you need to explain this to me: why is it that when that disease is in your neighbor’s field, on his velvetleaf, it doesn’t hurt his velvetleaf?” And sure enough, this disease existed right across the road, and it wasn’t hurting the velvetleaf.
Now I should have been able to figure this out quicker than I did. But I have to admit, I was quite dense, and I needed quite a few lessons and to notice quite a few things before I started putting two and two together. The next thing we noticed was a second disease in that velvetleaf that a student at Cornell identified as a virus. And in the meantime, because I was paying so much attention to thinking that this was going to be my new product, I noticed that those leaves were covered with white flecks. The first time I saw it, I crawled on the ground and I said, “Look at all these white flecks—my leaves are just being eaten alive.” And the agronomist said, “You better watch out—you’re not going to have a crop left with all these insects out here.” But then we looked at the corn and there aren’t any bugs on the corn. The corn was perfectly healthy and growing well; it was only the weeds that bugs on them.
So the insects were actually carrying the virus, and the fungus was blowing on and killing them. But it wasn’t this complex that was actually killing the plants—those were just opportunists. We had changed our system so that it had become a very unhealthy soil environment for the weeds. And because the weeds were unhealthy, all these pests were moving in and were attacking the weeds. It wasn’t really the pests that killed the weeds—the pests were just there because the weeds were so sick they weren’t fit to live.