Moth trap reports indicate an early start to the corn earworm (CEW) infestation window across the Corn Belt this growing season. In early July, CEW had already been identified in the south, including Louisiana, Mississippi and Tennessee.
The trend could lead to significant corn earworm activity in the Midwest later in the growing season. Moth traps have identified Ohio as an area that may be at a higher risk of yield loss due to possible insect infestation, so growers are urged to scout fields to determine if treatments are needed to avoid yield-crippling damage.
Damage from corn earworm is caused by the larvae as they feed on leaves, silks and developing kernels.
“CEW is a serious pest that is present in Ohio every year. The pest overwinters in some parts of Ohio and is present throughout the state on many crops including field corn, sweet corn, popcorn and many vegetable crops. Trapping data from Ohio State University indicates that while 2008 and 2009 were relatively low years for CEW, 2006 and 2007 were strong peak years in moth trapping programs,” said Jason Fettig, a Syngenta agronomist. “CEW is part of what we call the multi-pest complex, including black cutworm, fall armyworm, and Western bean cutworm that cost U.S. growers $1.1 billion per year. Growers often see some level of ear tip feeding that they may feel is not economically treatable with today’s available insecticide treatments.”
It is tough to get a handle on the economic threshold for CEW.
“Variations in crop yield, crop value, insect pressure, and control methods make an economic threshold is difficult to pin down for this pest,” Fettig said. “Additionally, due to the biology of the pest and the limited efficacy of our previous control strategies, economic control has been difficult for Ohio corn producers. Integrated pest management strategies for control of CEW center around labor-intensive field-scouting and moth-trapping activities.”
With the challenges of finding and treating the pest, it is easy to let CEW slip under the radar because of what appears to be limited damage they cause, but that small amount of damage can lead to other problems.
“Presence in sweet corn, supports the presence of CEW in commercial corn, however it is often overlooked because it frequently falls below economic threshold levels. Even though damage may be below economic levels, damage is still occurring. When the damage from black cutworm and Western bean are considered together, the damage is additive,” Fettig said. “A general rule of thumb is that 3 kernels damaged or fed on per ear equals 1 bushel per acre at a population of 30,000 plants per acre. CEW also increases ear molds that lead to mycotoxins in grain.”
Beginning in 2011, growers will have the option of planting seed with the new Agrisure Viptera 3111 trait stack to protect against corn earworm damage without relying on scouting and insecticide applications. The Agrisure Viptera 3111 trait offers in-seed control of 14 yield- and quality-robbing insects, including CEW. Improved insect control with the Agrisure Viptera 3111 trait stack also reduces the incidence of mycotoxin contamination from both aflatoxin and fumonosins.
“Due to the fact that the insects hatch and move quickly through the silk and into the ear, where they are unreachable by the insecticide, precise insecticide application timing is both critical and maddeningly difficult,” Fettig said. “The advent of new control options such as Syngenta’s Agrisure Viptera trait, allow for excellent control of CEW without the unpredictable results and intensive management required by traditional scout and spray programs. The best scouting strategy and timing for CEW is to select the Agrisure Viptera trait at planting time.”