What is in this article?:
- Earworm populations changing in North Carolina soybeans
- Bad worm year
• Corn earworms on soybeans are an annual problem in many soybean fields in east central North Carolina.
• A fourth generation of corn earworms emerges in late August but these earworms have trouble surviving the typical heat and rarely develop in numbers large enough to treat.
• Last year (2010) the fourth generation larvae didn’t just go away. In fact, they survived and developed all too well.
LATE SEASON SOYBEANS may be at greater risk from corn earworm damage in the future.
For most North Carolina soybean growers dealing with corn earworms is an annual problem, but typically by the time the dog days of summer arrive, the third and last generation of these pests has come and gone.
And it’s never been much of a problem past late July- or mid-August at the latest.
Long-time North Carolina Crop Consultant Danny Pierce says this scenario hasn’t played so well the past couple of years.
“Corn earworms on soybeans are an annual problem in many soybean fields in east central North Carolina where I work. This is an area west of Goldsboro and east of I-95,” Pierce says.
Historically the third generation of earworms shows up in late July and early August in very high numbers and many fields need to be treated in a short period of time. This is usually a 14-20 day period.
Pierce says growers are accustomed to scouting fields and making insecticide applications when needed up to early August. After this peak flight, or third flight, very few fields need treating, he says.
A fourth generation of corn earworms emerges in late August but these earworms have trouble surviving the typical heat and rarely develop in numbers large enough to treat.
In Perquimans County, in the northeast corner of North Carolina, veteran County Extension Coordinator Lewis Smith says he’s seen the same pattern in corn earworm flights the past couple of years.
“In 2010, we never had any real heavy flights of moths, but they just kept coming. I caught moths in traps as long as I kept my traps in the field. That was significantly different than what I’d seen in the past,” Smith says.
Last year there was a heavy moth flight early and second flight that was nearly as strong. Then, populations seemed to settle down, more like we are used to seeing. Then after Hurricane Irene came through the area we had these later flights.”
Smith says in two very different years weather wise the same trend of late arriving and surviving corn earworms occurred.
“In our part of the state, we were lucky last year because most of our wheat was planted early the previous year, so most of our double-crop soybeans were planted early and were past the growth stage that is typically damaged by corn earworms,” Smith says.
“For as long as I can remember, up to 2010, late arriving moths lay eggs and many hatch, but worms have very poor survivability. Because of this, scouting has always been relatively easy during that time of year. Many fields, depending on when they bloomed, had to only be scouted three times or so, Pierce says.
Last year (2010) the fourth generation larvae didn’t just go away. In fact, they survived and developed all too well. Pierce who has been scouting crops in North Carolina for a number of years, says 2010 was the first time he had seen this fourth generation of corn earworms cause a problem.