LAMBERTON, Minn. — When visiting with Bruce Potter, the conversation usually starts with, “So what’s the outlook for soybean aphids this year?” Potter is the integrated pest management specialist at the University of Minnesota Southwest Research and Outreach Center in Lamberton.
“We’re just starting to build,” Potter said. “A lot of soybean fields got a late start this year. And many aphids came off the buckthorn before soybeans were even off to a good start. Just a few ET (economic threshold) levels in some fields in northwestern and central Minnesota have been sprayed. But they’re spreading out now. We’ll just have to wait and see what the weather does.”
Q: Any location in Minnesota where they might be ready to fire up?
Potter: Yes, a few reports from northwest Minnesota. However, so far little activity here in west central and southern Minnesota. We’re seeing a lot of parasitism in some of these aphids in some fields at SWROC. That’s a good sign.
Q: What’s promoting the parasites?
Potter: What we’re seeing down here is a species that creates little black aphid mummies. The adult wasp lays an egg in the aphid and the larvae feeds inside the aphid, killing the aphid. This species attacks several species of aphids and has been expanding its range. We don’t know much about this particular genus of parasites. George Heimpel’s lab on the St. Paul campus has a very active program in biocontrol of soybean aphids and is documenting the effect of parasitoid wasps on soybean aphid populations across Minnesota.
Q: Could this be an important tool in the ongoing battle with aphids?
Potter: I think it’s already starting to make an impact. Back in 2000-2013 times we did not see very much parasitism of soybean aphids. Now parasites are becoming more common.
Q: What’s the aphid population across the soybean belt? Is Minnesota still leading the list?
Potter: Aphids are all over the Upper Midwest. They’re now showing up in Nebraska, Kansas and Missouri fields. But those are most likely moving in from up here. Minnesota, eastern South Dakota, southeast North Dakota and northern Iowa have the bigger issues. Unfortunately, we’re still the number-one area for producing soybean aphids.
Q: Why Minnesota?
Potter: I think part of it is our buckthorn prevalence. Buckthorn is the natural over-wintering species for aphids. Plus, some is climate. We’re not as hot and humid. In that kind of weather, there are more fungal parasites which are nature’s way of minimizing aphid populations. In this area, you’ve got canning crops often with soybeans planted after peas. Plus, we’ve always got some late-planted soybeans where aphids can ramp up before they move back to buckthorn.
Q: Are airplanes becoming the predominant tool to control pests?
Potter: Where you have canning crops which are all contract-produced, aerial sprays for many growers have become part of their overall crop management strategy. Sugarbeets much the same way, with field specialists working with growers on their entire pest management program. And if there is a substantial explosion of soybean aphids or other outbreaks later into the season, airplanes can help get large acres treated quickly. Also, with some pesticide applications, we’re seeing a better fit with an aerial attack.
Q: Why does it take so long in getting new pesticides introduced into the market?
Potter: It takes time to get clearance on a new product. Lots of hurdles to be cleared. Getting a new class of insecticide, or fungicide, or herbicide or trait is neither quick nor cheap. In integrated pest management, we talk about using threshold levels before spraying to keep these products viable as long as we can. With soybean aphids, we’re in a bind right now because we have only a limited number of products. Corn rootworm and BT (Bacillus thuringiensis) is much the same predicament. The RNAi trait in SmartStax Pro has received Environmental Protection Agency approval, but not export approval. So far, there’s only limited usage. So at this stage, I’m not certain how this will fit in. Also, because producers and applicators aren’t used to new products, there can be problems. Examples are drift concerns with dicamba. That happened early on with Roundup. With these new herbicides and new soybeans to fit these products, we’ve got a new learning curve once again.
Q: Iron chlorosis deficiencies seem more prevalent this spring. Why?
Potter: Blame the weather. We were wet in many areas this spring, plus very cool. In the Lamberton area, chlorosis is spotty — tending to follow alkali soil rims. But people need to watch for iron chlorsis that disappear and reappears because that is probably nematodes. Iron deficiency is more an early-season thing. But if it shows, then disappears, then shows again, it is a good indication of nematode issues.
Q: If that happens, then what?
Potter: First check the variety you planted. Maybe take some soil samples. Check roots. If you have a variety that is supposedly nematode resistant, then check our University variety trial releases to see how strong that resistance is. We do have fields where soybean cyst nematode have adapted to Pi 88788 and to a lesser extent, Peking resistance sources. Some time you may have to throw in a resistant variety such as Pekin. But if you have high nematode populations and iron deficiency chlorosis issues at the same time, you may want to stretch your rotation. Those nematodes tend to make everything else worse.
Q: Because commodity prices tanked from 2010, are producers adverse to purchasing pesticides?
Potter: Yes, I think so, but that is natural considering how tight break-evens are these days. However, integrated pest management concepts and decisions based on economic thresholds haven’t changed regardless of commodity prices. If you made a mistake when corn was $7, it likely stung a little bit more. By the same token, if you’ve got $7 corn out there, producers get a bit more squeamish if there’s also an insect out there. Insects don’t eat more when the corn price goes up!
Q: Are you surprised Minnesota has more acres of soybeans than corn this year?
Potter: No, not really. Lots of soybeans moved in replacing wheat in western parts of Minnesota. Corn acres are down because of input costs which are considerably more than soybeans. But if economics were a little more friendly for corn, I think we’d see the shift back to more corn acres. However, a potential problem with more soybean acres is more soybean pest issues. Here in southwest Minnesota, getting some of these acres back into corn has really helped lessen some of these disease issues of soybeans. But if we get into a 50-50 ratio between the two crops, soybean aphids and nematodes might become more prevalent.
Q: Are you satisfied with the genetic progress being made in soybeans?
Potter: Soybeans are tougher to breed than corn. Yields have been consistently going up in both crops. Sometimes we get so excited about a new product, Roundup for example, that it detracts emphasis in other areas of genetic research. Right now dicamba or 2,4-D-tolerant beans are the focus. These little stair steps tend to sidetrack our genetic research. We’re still making progress on nematode and disease resistance issues however.
Q: Will 2017 yields match 2016?
Potter: No, that won’t happen. Last year was exceptional any way you measure it. Corn has some thinner stands. It’s later this year. Weather at pollination is the next determiner. But I think the corn crop will look pretty good this year too. Soybeans are late. A lot are fairly short. At this stage, impossible to predict; but my guess is we won’t match last year.
Q: Are cover crops a growing necessity?
Potter: Easier to establish in soybeans is my first comment. Cover crops may help control weeds, but they also complicate herbicide choices. My interest is what cover crops do to insect pests. We definitely need more studies in that area.