Weed Control for Organic Soybeans w/ Dr. Erin Silva, PhD

Interview with Erin Silva, Associate Professor at the University of Wisconsin–Madison

Show Notes

What are the best weed control methods for organic soybeans? Dr. Erin Silva of the University of Wisconsin–Madison shares strategies for organic weed control, focusing on cover crops supplemented with blind tillage, in-row cultivation and crop rotations.

Learn more about Avé Organics: www.aveorganics.com 

Learn more about Erin Silva at the University of Wisconsin–Madison: www.plantpath.wisc.edu 

Connect with our guest on LinkedIn

#agriculture #farming #organicagriculture #organicfarming #soybeans #weedcontrol

Podcast Transcription

INTRO: Welcome to Organics Unpacked, a podcast for the business-minded organic grower, where we hear from top experts in the commercial organic industry. With a focus on the business elements of organic growing both in and out of the field, you will gain insight and grow your operation. This show is brought to you by Avé Organics, a Wilbur-Ellis company. Here’s our host, Tom Buman.

Outlook for Organic Soybeans

TOM: So, Erin, I know that, in today’s market, organic soybeans are really the hot commodity. We’re talking prices that are pushing $40 a bushel for organic soybeans. That sounds crazy, but where are we in organic soybeans? What’s the outlook for that?

ERIN: Organic soybeans have notoriously been a difficult crop for farmers to produce as opposed to corn, which tends to close canopy quicker and tends to be a bit easier with respect to weed management. Farmers are often challenged when approaching weed management of soybean crops. They tend to close canopy a bit slower, and because they’re a lower-growing crop, weeds tend to break through more prevalently than they do with corn. So, in my experience, farmers have often been a bit hesitant to expand their soybean acres because of the challenges with respect to weed management. Certainly, there are many organic farmers that can grow soybeans quite well. They’ve learned how to manage soybeans successfully within their crop rotations, within their specific environments. There’s still a lot of debate in terms of which crop do you plant first, corn and soybean, in terms of your planting sequence in a given year? I’ve found that planting a bit later helps with respect to weed management, being able to do some fall seed bedding, letting those weeds initially germinate, being able to do some field cultivation to knock those weeds back and then plant those soybeans into a warm soil that they’re able to come up quickly. And we’re able to do some initial blind cultivation to knock those weed populations back. The cleaner you can get the field at the start, the cleaner the field will be at the end. As we do with many organic row crops, delaying planting and getting that initial flush of weeds to germinate and then knocking those back is often important. There are some potential benefits of perhaps changing up your crop sequence a bit and maybe not growing soybeans after corn. If we look at trying to alter the sequence of our crops to account for changing the different growth habits of those crops, the planting and harvest dates, that can benefit weed management. So, oftentimes, I find that farmers are growing soybeans after corn. So they’re following a vigorous 30-inch row crop with another crop planted on 30-inch rows that is a bit less competitive with weeds, and I think that’s often challenging. So looking at maybe changing up your crop sequence and then finally looking at supplemental weed management if there are breakthrough weeds mid-season. So it’s not unheard of for organic farmers to hire crews to walk the fields and clean up weeds by hand, as well as using some more innovative tools such as the Weed Zapper to go above the crop canopy and kill some of those weeds that may have escaped some of those initial weed management events.

Cover Crops for Organic Soybeans

TOM: So, Erin, let’s talk about cover crops a little bit and maybe no-till. I think I saw you referred in one of your videos to maybe intensive cover crops. How do you recommend farmers using cover crops in a soybean situation?

ERIN: With soybeans, a large part of our research program has involved using cover crop-based no-till to facilitate weed management in soybeans. So that involves using cover crops that are strategically planted in the fall. And typically, we’re using cereal rye, although other winter cereal grains can be used such as winter triticale. But winter cereal rye has really proven consistent with this system because it tends to overwinter very well across a wide range of environments, as well as has allelopathic properties. That tends to suppress weeds from germinating. We plant cereal rye, and I hate to even say fall because, really, farmers need to think about planting cereal rye in the late summer. You need to plant that cereal rye much earlier than you typically would as a cover crop that you might be putting on the ground to protect the soil from wind or water erosion. So, in Wisconsin, we’re aiming to plant that crop anytime between the beginning of September to the middle of September. And this is really critically important to get the weed suppression in the spring and the summer — season-long weed suppression, honestly, in the soybean cash crop — because it’s not only related to the biomass in terms of weed suppression but also the ground cover. And that earlier planting allows for tillering that allows that cover crop to cover the entire field even very early on in the season in April. So planting that cover crop early is really critically important to the success of the system. And that often requires rethinking in terms of crop sequence. 

So coming in after corn harvest, which is typically occurring anytime between late September and late October, can be really challenging for the success of the system. So looking at putting the soybeans after another winter cereal rye crop such as wheat or potentially oat as a spring-seeded cereal grain or a cover crop or another alternative crop. So, after that cover crop is planted in late summer, it continues to survive throughout the winter in a dormant state and starts regrowing in the spring. Then we terminate that cover crop mechanically using a roller crimper at the stage of anthesis, which is when the pollen starts to be shedding over those cereal rye heads. So, at that time, we roll over the field using a roller crimper, and that mechanical action of the roller crimper terminates that cover crop. And we’re able to plant the soybeans at the same time at termination. And that cover crop essentially puts a mulch across the surface of the field, similarly to how you’d apply straw or newspaper or cardboard to your garden, and prevents sunlight from reaching the soil surface, as well as tying up some nutrients that prevents weeds from germinating. So that cover crop not only allows us benefits with respect to soil health and protecting our soil but, really, is our entire weed management program throughout that soybean cash crop growing season.

Replacing Cultivation with Cover Crops

TOM: When you’re using a cover crop, you’re really replacing the cover crop with tillage. Where, in the past, you’ve done weed control with tillage, now you’re really doing the weed control with the cover crop. Is that fair to say?

ERIN: Yeah, within in-season, so that cover crop replaces the cultivation. There is opportunity to do some cultivation if you do get breakthrough weeds using high-residue cultivators, so cultivation isn’t completely off the table. And certainly, the other strategies of multi-year ecological weed management in organics still apply to this system. Looking at minimizing weed seed rain, keeping weeds from going to seed, allowing for diversity within the crop rotation, using cover crops strategically across multiple years, those are all still critically important. This cover crop-based no-till technique is not going to clean up weeds in a field that have become excessively high in numbers. If you do have a very weedy field, this is not a technique that’s going to help clean up that field. Those ecological strategies across multiple years are still critically important. But within a given season, this allows for weed suppression that can replace cultivation.

Rotating Cover Crops

TOM: If you are going to go to cover crops, and you have the opportunity to do that because maybe you’ve suppressed weeds and you’ve got them under control in the past, it sounds like you have to think about maybe changing up your crop rotation a little bit.

ERIN: I find that farmers that are trying to do this coming in after corn, oftentimes, don’t get the biomass and the ground cover that they need. And that’s where we see some of our failures in this system with respect to weed suppression. So, again, you’re looking at coming in after other crops. In our experiments, we are coming in, again, after another winter cereal grain, after an oat crop. Sometimes we’re terminating an alfalfa stand a bit early. Or sometimes we’re doing what we call a biointensive year, a soil-building year where we’re using a cover crop to build up that soil, and then coming in after that soil-building phase. We’ve used various approaches. Another approach that is feasible in Wisconsin is to come in after corn silage, which tends to come off a little bit earlier than corn for grain. So we’re able to choose an early-maturing silage variety and still plant our cover crop in the right window. We’re able to have a successful organic no-till soybean crop. But there does need to be some strategic thinking in terms of what you plant, that you’re able to get off the field early enough to get that cereal rye cover crop planted within the window that’s necessary for a successful roller crimp crop.

Organic Soybean Yields

TOM: So, for people that are kind of new to organic farming, and they’re maybe in the transition time or just thinking about it, Erin, what kind of yields can you expect in Wisconsin on organic soybeans?

ERIN: I can only speak for my own experience, that we at the University of Wisconsin – Madison have hosted a long-term organic cropping systems trial. This cropping systems trial started in the 1980s, late 1980s, by Dr. Josh Posner from the Department of Agronomy. And that cropping systems trial compares conventional corn/​soybean rotation and organic corn/​soybean/​wheat rotation. It’s managed using certified organic practices, and we’re able to really look at trends over multiple years. It’s probably important to note that this is southern Wisconsin, and it is on very rich Mollisol prairie soil. So we definitely are blessed with a very good soil environment. But what’s been seen over those last 30 years is that, in a year, we’re able to implement timely weed management. We are able to get organic soybean yields within 95% of conventional yields, so our soybeans are quite competitive. And within my research plots, I’ve had soybean yields into the 50 – 60 bushel per acre range fairly regularly, definitely within the 45-to-50 bushel/​acre range consistently and, again, up to 60 and even 70 bushels an acre. But that’s really dependent on good weed management. What that long-term systems trial found was that, in years where weed management is challenging, which typically is because farmers are kept out of the field because of weather, that’s when you see soybeans lag. So this weed-managed component is really critical. But if that’s put in place, our soybean yields can be very, very competitive with conventional soybean yields.

TOM: That’s impressive. I mean, given the increase in price per bushel and to get that kind of yield, that is really impressive.

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