While a persistent pest in many soybean-producing areas of the upper Midwest, soybean aphids hadn’t been found further south than Kentucky until their discovery in Rutherford County southeast of Nashville in middle Tennessee several weeks ago.
“Bud Twitty, who’s with Pioneer Seed Co., had been out in some Rutherford County soybean fields and noticed the aphids,” says Russ Patrick, Tennessee Extension soybean entomologist. “He called me and said he thought there might be aphids colonizing on soybeans because he’d found aphids of all maturity.
“We went out around Eagleville and checked and, sure enough, Twitty’s description was right on. We sent some samples into the University of Illinois and got confirmation this morning that, indeed, soybean aphids are what we’ve got.”
Since the initial discovery, soybean aphids have also been confirmed in Williamson County (around Franklin where populations of 50-plus aphids per leaf were noted) in middle Tennessee and Madison County (where Patrick found the pest on West Tennessee Experiment Station fields around Jackson) in west Tennessee. Patrick suspects the pest may have spread even further.
“I wouldn’t be surprised if this pest isn’t in just about every soybean-growing part of the state.”
Earlier this season, Illinois researchers reported a huge aphid flight that reached all the way into the southern tip of their state, which is about 40 miles from the northwest corner of Tennessee.
“That’s probably where our aphids came from,” said Patrick. “I don’t think this has anything to do with all the late soybeans. I believe this is just a case of the pest taking advantage of a situation and expanding their range.”
He said the pest could have already moved into other states given the close proximity of southern Illinois to northeast Arkansas.
“We’re going to watch the aphids this fall and see if they survive the winter,” he noted. “We need to know if they’re actually going to overwinter here.”
Patrick says he’s been told soybean aphids will overwinter on common buckthorn.
“I’ve also heard they’ll overwinter on kudzu. If that’s true, they won’t have a hard time making it in the South. Kudzu is everywhere.”
As far as Patrick knows, there are no established thresholds in the Delta yet.
“States to the north have thresholds going up as high as 200 aphids per plant or 25 aphids per leaf. Most soybean insecticides labeled for aphids will control this pest with no problem. But, as far as I know, soybean aphids specifically aren’t on any of the labels down here yet. If it says ‘aphid’ on the label, though, that should be sufficient.”
The problem with the pest is its reproductive ability. Soybean aphids can move through generations “very, very fast. When soybean plants are young – maybe flowering stage or younger – the pest can hit the trifoliate leaves or terminals in huge numbers. When the terminals are hit, yields are hurt. Right now, with our crop in pod-fill stage, the soybean aphids aren’t likely to hurt anything. It’s early next year we’ve got to watch out for.”
With that in mind, through the winter Tennessee Extension will be cautioning producers to really keep an eye out for soybean aphids come spring.
“We don’t want anyone to panic, but everyone should know this pest is now here,” says Patrick. “And if the population builds up, there are dangers to the soybean crop.”