In southwest Tennessee, some farmers have been planting corn for over a week. “Producers go early there,” says Angela Thompson, Tennessee Extension corn and soybean specialist. “They try to get corn in so they can move on to cotton.”
While those farmers hope a strong soybean crop wiggles out of the soil, they're keeping an eye out for an unwelcome guest. Last year, for the first time, soybean aphids showed up in Tennessee fields (in two central and three western counties).
“When this pest showed up in our borders, we immediately knew that the potential for damage to our soybean acreage had jumped,” says Russ Patrick, Tennessee Extension entomologist. “Yield loss with this pest can be severe — it is in Michigan, Illinois and northern Midwest states. Luckily, that didn't happen here.”
But the unknowns still have Thompson and Patrick worried. “We don't even know if soybean aphids (sometimes called Chinese aphids) are overwintering in the state,” says Thompson. “We need to find out if that's the case. Based on producer comments during winter meetings, there is a real concern about soybean aphids. Producers are well-informed and know that soybean aphids in the upper Midwest are a real problem. They also know that sometimes treatment isn't always successful.”
Thompson, Patrick and Scott Stewart (an Extension cotton entomologist) decided there was a need to keep an eye on the situation. This winter, they applied for program funding from the Tennessee Soybean Promotion Board. “The board agreed that we need to monitor this pest,” says Patrick.
Tennessee Extension agents will be “incredibly important” in this effort. Agents will identify producers with appropriate soybean fields to work — close to main roads so samplers can keep on the move. Repeated sampling will be done in at least two fields per county involved in the study.
By monitoring fields, “we should be able to see if the aphids show up soon,” says Patrick. “If the pest does show up early, that's a good indication it's overwintering in the state. If it is overwintering, then we really need to keep an eye out — early on in the growing season is when this pest can do the most damage to a crop.”
If the soybean aphids have overwintered, Thompson says, researchers should know sometime in May. “We should have an answer to that question within six weeks or so. Maybe they're not overwintering and coming in on storm systems. Regardless, we need to know.”
Last year, soybean aphids were found late. At that point, it wouldn't have benefited farmers to spray.
“We have only tentative threshold limits, because we're basing them on other states' (thresholds). Right now, depending on the stage of growth, Tennessee's threshold is about 250 aphids per plant,” says Patrick. “Treatment thresholds are lowest during early bloom — that's when aphids can really hurt your crop. We do have labels for soybean aphid control.”
Damage to plants from soybean aphids can include: stunting, discoloration, distortion of leaves, reduced pod seed counts and yield loss. The accumulation of honeydew on leaves can result in mold — a problem that can reduce the plant's photosynthetic ability. The pest is also capable of transmitting plant viruses (such as soybean mosaic virus) that can lead to yield loss.
There are several bad things about this particular aphid, says Patrick. “It can multiply very fast. You might find a couple hundred on a plant and a few days later there will be 800. They're prolific reproducers. And, obviously, the more aphids, the more damage to plants.”
Although the soybean aphid tops the list of concerns, the monitoring program will also allow other pests to be tracked. “This is an excellent opportunity,” says Patrick. “We've always had problems with stink bugs and we'll be able to keep them under surveillance. Also — and hopefully we'll never see it — we can watch out for soybean rust. We'll also be looking for things like frogeye leaf spot.”
Tennessee corn also has a nasty pest to fear. Over the last couple of years, in several west and central Tennessee counties, producers have found corn fields hosting the sugar cane beetle. It isn't an epidemic, but corn that was hit was often hurt badly, says Patrick — sometimes 30 to 40 percent damage in a field.
“This is a bad insect that hits young corn hard,” he says. “When corn comes up in the spring, the adult beetles will work straight down a row. It typically feeds below ground, on the roots or base of the stem, and that leads to the plant dying or to easy avenues for disease. This beetle is a very difficult pest to control.”
Tennessee corn has been sprayed for sugarcane beetle. It's estimated that between 14,000 and 15,000 corn acres were treated last year. “We haven't found any insecticide treatments that were completely successful,” says Thompson. “But we've learned a lot. This year, we're going to take the knowledge we gained and expand on it. We'll be checking out Poncho 250, which is an intriguing product. Roger Leonard at Louisiana State University has had success with Poncho at higher rates.”
Also, if it stays cool and damp, producers need to watch out for cutworm problems, says Patrick. Cutworms are usually spotty across the state, but low-bottom fields are especially vulnerable.
“The best method for dealing with cutworms is scouting and, if needed, an over-the-top recommended insecticide,” he says. “To save money, many producers don't put insecticides out at planting. If they don't want to do that, they may want to consider a seed treatment. The effectiveness of seed treatments on cutworm and sugarcane beetles is still being investigated, but may have promise, at least at higher rates. These seed treatments will also control wireworms and several other pests.”
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