The number of armyworms munching their way through Arkansas' wheat crop is “the worst I've ever seen. Nearly all the wheat in the 50- to 60-bushel range must be sprayed,” says Arkansas Extension wheat specialist William Johnson.
“We started getting armyworm reports about two weeks ago from southeast Arkansas. Last week, the reports came from Marianna, Stuttgart and all through that region,” says Johnson.
Normally, five to 10 armyworms per square foot is a pretty heavy infestation. This year, 30 to 35 per square foot is fairly common, says Johnson. And there have been fields with 70-plus worms per square foot found.
“One of our research fields in Marianna is a prime example of how these things operate. We had a field day (the last week of April). The day before the field day, the counts were at 35 to 40 per square foot and they were just beginning to feed on the leaves. We waited until the day after the tour to spray and by that time the worms were already cutting on the flag-leaf.”
Calls to the Extension Service have begun to subside but are still coming in steadily. “Lots of consultants are calling letting us know what's happening. Any wheat with nice yields is vulnerable. You can pull back the canopy and the ground moves.”
It appears the more winter junk weeds in a field, the higher the armyworm population is. Some of the junk weeds appear to attract moths, says Johnson.
Arkansas Extension entomologist Don Johnson agrees. “We have winter weeds that get into wheat. The armyworms tend to prefer fields that have a lot of these and lay a lot of eggs.”
In general, when looking at pests, Don Johnson says there's a need to differentiate between native and non-native insects. The past winter probably didn't hurt the natives much, he says.
“The pests it knocked back were those that tend to be tropical — some of the beet armyworms, fall armyworms. There's an outbreak of true armyworms in wheat right now, though. This is the most serious outbreak I've seen in around 15 years.
“If you look at the extreme populations, the highest number we counted yesterday (May 2) was 78 per square foot. That's a huge number.
“There are other fields we checked that had 4 per square foot, so there is a balance. The threshold to spray is between 6 and 8 per square foot,” he says.
How and why did such numbers occur?
The armyworms tend to pupate 3 to 4 inches below the soil surface. That affords them protection from the cold. Obviously the freeze the Delta experienced didn't get deep enough into the ground to affect the armyworms.
“We had some moth traps out early on. Those traps gave every indication that numbers of armyworms would be higher than in recent years.
“The traps were averaging about 40 moths per night early on. The highest number we had last year was around 30. So we knew the numbers would be higher than last year.
“We didn't know they'd show up quite like this, though,” says Don Johnson.
William Johnson believes the state will still make a good wheat crop, “provided everyone sprayed as much as we think they did. We're probably looking at a 51- to 52-bushel state average. That's not as good as last year. We have too many holes in the fields.
“There's no disease in the fields and it's cheaper to control armyworms than disease. That's a plus.”
Meanwhile, corn is going in like crazy, he says.
“There's an amazing amount of corn going in around Holly Grove, Ark. For whatever reason, there have been some complaints about the boll weevil eradication program over there. Corn is going in big-time. There's hardly any fields over there not in wheat or corn.”
What concerns does Don Johnson have about the coming growing season?
“In cotton we're still concerned with tobacco budworms, especially in the eradication area where there's a lot of malathion going out. They tend to be a bit more severe in those areas.
“There's also some concern about the fall armyworm. We had a lot of them last year and they impacted cotton. But where they were worst was in our pastures. They really hurt good bermudagrass. As a result, we've submitted a Section 18 for Tracer.”