Much has been invested in recent years in learning how to detect and control Asian soybean rust, says Dennis Delaney, Auburn University Extension soybean specialist.
“We’ve had a lot of finds in the past couple of weeks as soybeans start to mature and the weather cools and we get a little more rain. We’ve found it in 22 Alabama counties,” said Delaney in mid-September during a central Alabama crops tour.
The disease also has been found in the Memphis area and in Arkansas. “I’m fairly certain most states have some level of soybean rust. But most of the time, it has been really late when we find it, it is at low levels, and it’s not enough to cause much damage,” says Delaney.
Later double-cropped soybeans could still be in danger, he cautions, especially if there is an increase in rainfall. “If the beans get to R-6 — when soybeans touch one another in pods — then we don’t worry about rust anymore. They’ll go ahead and fill out even if rust comes in the field.
“Before that, when the beans are small in the pod and not yet touching, we recommend coming in with one of the triazole fungicides — just enough to carry you a few weeks until you do get into that R-6 stage. If they’re still in the small pod stage, and you have good yield potential, it’s recommended that you go in with a strobilurin and triazole combination. Basically, timing is the most important factor,” says Delaney.
Growers also need to be concerned about other soybean diseases, including leaf blight and frogeye. “Some of these other diseases can take away just as much yield as Asian soybean rust if you let them get out of control. It’s important that we apply those fungicides, especially during the wet spells. But May and June-planted beans are probably past that.
“We’ve looked at applying fungicides on soybeans early. In the first three years, we saw about a six-bushel yield increase when we put out fungicides early. And for the next three years, we didn’t get any yield bump. So you need to look at the weather and decide if early applications would be beneficial.
Auburn University Extension Entomologist Ron Smith says the main insect soybean producers need to be concerned about at this point in the season is the stink bug. “There are a lot of late-maturing beans in Alabama this year, but the stink bug has really built into high levels in soybeans right now. It’s a strange phenomenon. You’ve got to be watching soybeans regularly to see it, but they will show up overnight, when beans get to a stage to where stink bugs can feed on them. Then they’ll move onto something else,” says Smith.
During the first part of September, Smith says he was working with foliage-feeding pests and stink bugs showed up overnight, more than one per row foot.
“Caterpillar pests, as far as foliage feeders, have been really light on soybeans this year. We’ve had some level of sub-threshold levels all season long of green clover worms, loopers and fall armyworms, but we haven’t had economic levels of foliage-feeding worms, and it takes about five to eight per row foot to be at treatable levels,” he says.
Podworms have been virtually non-existent on Alabama soybeans this year, notes Smith, though they can still feed on a pod until it hardens.
“One other thing we need to be aware of is the soybean aphid,” he says. “It primarily has been a Midwestern problem, but we were getting reports earlier this year from North Carolina, Tennessee and Kentucky. We found them very widely distributed in north Alabama’s Tennessee Valley. We’re not sure exactly what this means. We don’t think it presents a tremendous potential for a problem down here, but we don’t fully know yet what it’ll do. They are in Alabama right now and distributed in the Tennessee Valley,” he says.