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Cutworms Threaten Corn Seedlings

Cutworms Threaten Corn Seedlings

Black cutworm moth trap counts and weather conditions indicate increased likelihood of cutworm infestations on corn in Iowa. As corn begins to emerge, growers should scout corn fields and keep doing it regularly, at least once a week, to determine if insecticide applications are necessary.

Recent black cutworm moth flights in the southern U.S. have caused concern for corn farmers in the northern U.S., including Iowa and surrounding states. Each spring, black cutworm moths fly into Iowa and the northern Corn Belt from the south and lay eggs in fields. It's those eggs which hatch and become the larvae (worm stage or caterpillar stage) of black cutworm.

"I encourage farmers to start scouting their corn fields now, beginning when the corn emerges," says Erin Hodgson, an Iowa State University Extension entomologist. "And you should continue scouting your fields until the corn has developed 5 true leaves, which is the V5 stage of corn growth."  

Estimated black cutworm larvae cutting dates for each Iowa crop reporting district is based on the first recorded peak flights of the adult black cutworm moths that occurred in the spring of 2011.

If black cutworm larvae are less than three-quarters of an inch long, and you have 2% to 3% of the plants infested, you're probably justified in applying an insecticide spray to protect yields, she points out. If the cutworm larvae or caterpillars get over three-quarters of an inch long, the threshold is increased to about 5% infestation.

Doesn't take too many hungry cutworms to decimate a field  

"The fields of particular risk at this time of year are those that are weedy or have reduced tillage or no-till," adds Hodgson. They are the fields most attractive to the cutworm moths which lay eggs there and feed on tiny weeds. The eggs hatch and become cutworm larvae which can chew on corn plants and cut them off.

"Fields at risk of black cutworm infestations also include low-lying fields or poorly drained soils or any parts of fields that are bordering grassy areas or that may have a rye cover crop," says Hodgson. "We would expect corn to be cut by black cutworms in different parts of Iowa at different dates. Our projected dates for cutting to begin this year range from May 15 to May 22, based on when you planted and when the corn is starting to emerge."

 Scouting should begin several days before the predicted cutting date.

The estimated cutting dates for the various crop reporting districts in Iowa are: May 15 in southwest; May 17 in south central and southeast; May 19 in west central and east central; May 20 in central; and May 22 in all three northern districts. These predictions are based on actual and historical degree day data accumulated from the dates of the first peak flights. Scouts are encouraged to start looking a few days before the estimated cutting dates as development in some areas may be sped up (or slowed down) by localized climate conditions.

States across Corn Belt are reporting intensive moth trap counts

Agronomists in states across the Corn Belt are reporting intensive moth trap counts of black cutworm. Moth trap counts are a good way to identify locations where eggs may have been laid as well as regions that are at higher risk of future damage from the newly hatched larvae that like to feed on young corn plants. Increased levels of moth flights are often the first sign of heavy egg-laying and possible infestations later in the season. Seed company agronomists say corn fields in Illinois, Indiana, Iowa, Kansas and Missouri are at possible risk.

Growers are urged to scout fields now because black cutworm can cause substantial damage to growers' yield potential if not controlled early in the growing season. Infestations can lead to stand reductions of more than 70% in some sections of fields. Agronomists for Syngenta Seed Company recommend scouting by checking 20 plants in five locations every 25 to 30 acres. If the total of damaged plants exceeds 2% and larvae are smaller than three-fourths of an inch in length, consider treating with an insecticide. As larvae and corn increase in size, the threshold can be raised to 5%; however, if the current stand is less than 15% below optimum, they say you should maintain the 2% threshold.

Advanced corn traits and trait stacks can defend against pests

"Growers should be aware of the increased possibility for black cutworm infestations, especially in no-till fields with annual weeds," says Bruce Battles, Syngenta's agronomy marketing manager. "Unfortunately, weather patterns across the Corn Belt this past winter and spring created field conditions in which black cutworm populations tend to proliferate. Growers can look to Syngenta's advanced corn traits and trait stacks, like the Agrisure Viptera 3111 trait stack, to help them protect their investment by providing black cutworm control."

To protect against black cutworm all season long, growers can plant corn hybrids with the Agrisure Viptera 3111 trait stack, he says. This stack combines the Agrisure Viptera trait with the Agrisure3000GT trait stack to provide control of 14 above- and below-ground corn pests. Corn with this combined trait stack also has herbicide tolerance to glufosinate  and glyphosate.

In-seed trait stack provides defense against multi-pest complex

He adds, "Corn hybrids with Agrisure Viptera 3111 trait stack have an in-seed defense against the multi-pest complex, including black cutworm, corn earworm, fall armyworm, Western bean cutworm, dingy cutworm and stalk borer, among others. Syngenta estimates damage from these pests costs U.S. corn growers 238 million bushels of corn and $1.1 billion in annual yield and grain quality losses. In recent field trials, the Agrisure Viptera 3111 trait stack nationally delivered a 7.3 bu./acreadvantage under ear-feeding insect pressure."

The Agrisure Viptera trait is approved for cultivation in the U.S., Canada and Brazil, and is approved for import into Australia, Canada, Mexico, the Philippines, Japan, Taiwan, New Zealand and South Korea.

Currently, the Agrisure Viptera trait is available in hybrids from the Garst, Golden Harvest and NK brands from Syngenta and will also be made available through licensing agreements with over 125 local and independently owned seed companies. Growers can contact a local Garst, Golden Harvest or NK representative to find out where they can view hybrids with the Agrisure Viptera trait in action at Syngenta field trials this summer. For more information about the Agrisure Viptera 3111 trait stack, visit

TAGS: Extension
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