Features Q & A
The potato vine crusher

Andrew McKenzie-Gopsill, a weed scientist with Agriculture and Agri-Food Canada (AAFC) in Charlottetown, P.E.I., was a recent guest on Potatoes in Canada’s (PIC) podcast Tuber Talk, and he outlined his research on a piece of equipment called the “potato vine crusher.” This device is used to help control the European corn borer (ECB) population and has successfully reduced these pests in the field, but its ability to fly between fields means all farms in a given area would have to employ the technology to see a beneficial effect overall.

McKenzie-Gopsill discusses the history of the potato vine crusher and the trials he is running to determine its potential for weed seed management.

PIC: Potatoes seem to be a high-risk, high-reward crop. Can you share a little bit about the background of the potato vine crusher and the research AAFC scientists were using it for about 10 years ago?

McKenzie-Gopsill: This system was originally designed by our entomologist here at the Charlottetown Research Centre, Dr. Christine Noronha. She’s done a lot of work on potato pests, more recently on wireworm. A little over 10 years ago now, she had a project -– I think it was involved with the Pesticide Risk Reduction Program – looking at trying to reduce pesticide use in potato production. She came up with this system to control European corn borer larvae that overwinter in desiccated potato stems. This system was just a set of rollers that attached to the back of the potato harvester. Then, as the potatoes were being harvested, the vines that would normally just be dumped back onto the ground are fed with a set of brushes into those rollers and then crushed and dropped back on the field. She never published anything on it. No peer reviewed manuscripts, but you can find some fact sheets online on the AAFC website. She was getting [around] 95 to 100 per cent control of this larvae. So, a huge reduction in the population of that overwintering European corn borer larvae. Unfortunately, the European corn borer is mobile, it will fly around, so even though you may control all of the borer population within your fields, they can just fly in from neighbouring fields the next season. So, the vine crusher for control of European corn borer is really going to be a community approach. You need everybody within an area to be managing this or to be all proactively using this to try and manage it to have a big effect on European foreign-born populations within a locality. I think that kind of was what killed the vine crusher at that time.

Then, I was doing a presentation at the University of Prince Edward Island, and it was to the fourth-year undergrad thesis class. When I got to a slide about harvest wheat seed control, which is a relatively new paradigm in weed science, all about managing the weed seed bank and trying to remove weeds or revitalizing or destroying weeds in the field. I was talking about this concept and [someone] said, “We have the system that we developed that was in the back of potato arcs that might be useful for this because all harvest weed seed control systems that exist right now are for crops that are combined.” Any other systems like the Harrington Seed Destructor, which would probably be the most well-known, that is either a tow-behind unit from on the back of the green combine or is fully integrated into the back of a combine.

Obviously, potatoes are not harvested with the combine, it’s the custom harvester, so we can’t employ any of the kind of traditional harvest routine practices. The vine crusher had just been sitting at our research farm up in the rafters collecting dust for the past 10 years. That kind of led me to the study and the work we’ve been doing over the last little bit.

PIC: When was it that you started the work on considering weed control with it?

McKenzie-Gopsill: There are a couple of different variables that we can evaluate on the vine crusher. There are two main variables we could play around with trying to optimize control. One is the tension that pulls the rollers together. That is set by a spring that is either adjusted by compressing it, and then there’s the speed that the rollers actually spin. We wanted to initially determine how to look at roller retention. So, we had to figure out a way to measure spring compression. My grad student and I went to a local gym and we’re sitting there putting weights on top of these springs to try and generate a spring constant, which would be how much tension is applied or force is being applied on the spring based on how much you’re compressing it. We figured all that out and then COVID-19 happened. That kind of shut us all down. We were all set to go. We had all the experiments designed and then we weren’t able to get back into our research farm for quite a few months. I think all this testing ended up actually happening in the winter of 2020 and then over into 2021.

PIC: I imagine it takes a bit more spring tension to crush weed seeds and insects.

McKenzie-Gopsill: Yes. We initially designed two sets of experiments to try and optimize both roller speed and spring tension. We started with spring tension, and we decided to look at one species in particular – common lambsquarters. My labs documented resistance to Sencor Metribuzin, which is the number one product that potato producers in our region use and rely on for weed management. We’re around 50 per cent of our populations in potato fields are resistant to Sencor. So, we decided to do all our initial testing using that species and we learned a little bit of some interesting biology with that species while testing. The seeds are very small, so you’re dealing with a two-millimeter diameter seed. That was another thing if we could figure it out; if we could crush a really small seed, we’d probably have greater efficacy on a larger seed and any kind of those grasses like barnyard grass or yellow foxtail. We did find a big effect of roller tension. Not surprisingly, as we increased our roller tension, which pulled those rollers together, we got greater efficacy. But interestingly, when we started crushing our lambsquarters seeds, as we increase the tension, we saw germination actually went up. So, two things that we think are going on there. One is that we’re breaking dormancy of the seeds and it’s resulted in an increase in germination. Two, which was the kind of interesting part that we had never seen before, is when you crush it lambsquarters seed, sometimes one half of it will still germinate. We did it initially in a petri plate and then we went over and put them into field soil, and under field we get a reduction in germination. So, what we think is happening is it’s not likely a plant can survive. It’s missing its root or its developing meristem. It resulted in fatal germination when we put it on the field soil.

PIC: Since this technology enables farmers to not build their own machines, and it doesn’t come like a package deal, it makes it a lot simpler for them to know that one aspect is kind of the important one when dealing with seed mortality.

McKenzie-Gopsill: Yes. It’s very important to keep those rollers in place. Once we optimized those, the roller tension and the roller speed, we tested the system out on five different species. Again, we want common lambsquarters and ragweed pigweed to very small seeds. And then we went with three seed species that are a bit larger, so yellow foxtail, barnyard grass and then a volunteer canola seed. We saw much higher efficacy on all of those larger weed seeds, probably because you’re getting more tension – there’s a tiny gap for that seed to pass through. With lambsquarters we were getting about 65 per cent control under controlled conditions in our Petri plates. All of our other species, it was ranging between 87 and 94 per cent. So, really high efficacy on controlling any of those. We were basically dealing with something like a canola crusher where we could see canola oil on our roller after crushing them.

Then for the next experiment we wanted to get as close as we could under controlled conditions to a potato harvest, so we took all our weed seeds, instead of doing them all in isolation, we mixed them all together, along with some potato biomass and sent that all through at the same time. Here’s where we saw again, greater efficacy on our large weed seeds, but there was just too much variability with our small seeds. What’s probably happening is that potato biomass, or there’s large weed seeds, were pushing those rollers apart slightly, and then letting all those small seeds fall through. So, in some situations, we got good control, some situations we got a moderate control; just a lot of variability there, all because those small seeds could pass right through. So again, emphasizing how important it is to have those rollers close together. But also, as you mentioned, how producers can just build this themselves, because there’s no IP controlling this. It’s freely available to the public.

PIC: If the biomass is going through, does that control the European corn borer, as well?

McKenzie-Gopsill: Yes, so it is kind of like an IPM. You’re potentially getting some insect management, as well as some weed seed control there.

PIC: You spoke of the Harrington Seed Destroyer and how weed seed crushing is not necessarily a new technology in that field. What does it do when it crushes the seeds to essentially kill them off?

McKenzie-Gopsill: The development of this technology is really a response to the herbicide-resistant issues that producers face. If you’re dealing with a herbicide-resistant weed, it is going to escape your herbicide and then set seed. The biggest effect you can have on a weed or herbicide-resistant population is in that first year after resistance develops, if you can prevent those seeds from getting back in the field, then you may have had resistance developed but it’s not going to spread. Using this type of system, if you’re at the really early stages where resistance is just developing, hopefully you can remove those seeds from the field and then you’re not going to have that herbicide-resistant population there. If you already have resistance, this system can reduce the amount of seed that’s there. So, you’re just reducing your weed pressure overall, so having an impact on your population within that individual field. There’s a study just published within the last year from some weed scientists down in the U.S. where they’re dealing looking at harvest weed seed control on Palmer Amaranth, which is resistant to pretty much everything we throw at it. And, from some of their simulations, they show that harvest weed seed control as low as 20 per cent efficacy – removing 20 per cent of the seeds that would normally go back into the system – will maintain our populations. So, if we have any greater efficacy, then we’re going to have a reduction in our population. But as long as we can maintain a 20 per cent efficacy, which our system here has greater efficacy than that at least under the conditions that we’ve evaluated so far, then we can have a positive effect on reducing our population within that field of whatever particular weed we’re targeting.

PIC: Will this summer see field tests or is it still a little ways off from that?

McKenzie-Gopsill: We are hoping to field test this year. I didn’t have any fields that were suitable last year, but this year, we’ve got some potato fields out at our research farm, so we’ll be field testing this, harvesting potatoes and then doing some seed-bank measurements comparing using the potato vine crusher versus not using the potato vine crusher and seeing if we’re having an effect on the weed seed bank there.

PIC: What are the implications for potato growers, and is this something potato growers can access currently?

McKenzie-Gopsill: The plans are freely available. Anybody can build this system if they like. Logistically, it should work. It shouldn’t interfere with the potato operation. It’s not going to gum up your harvest or anything like that. Whether or not it actually has an effect on the weed seeds, we don’t know. We’ll hopefully evaluate some of that this season. But yes, it’s a system that’s available to potato producers right now that they can start building and attaching their equipment to and at least control European corn borer larvae and potentially control some weed seeds at the same time.