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Black Cutworm Update

05/11/2012 @ 3:42pm

Most of us enjoyed the warmer than usual temperatures of last winter, but mild winters can have a downside.   That downside is showing up in central Missouri and moving northward in the form of above normal Black Cutworm Moth flights.   Cutworms are being found right now in Central and SW Mo.  Below are two pictures of cutworms at different instars found in the same Missouri River bottom field.  The presence of more than one instar of larvae indicates multiply moth flights and egg laying's.


Scouting for Black Cutworms

Adult cutworm moths prefer to lay their eggs in fields that have an abundance of vegetation.  For example field that is overgrown with winter annual weeds like henbit, chickweed, and peppergrass.  They also gravitate towards low spots in fields or overflow ground.  The entire life cycle takes more than 45 days from egg to adult.  This process continues all summer long until the first frost when adult moths migrate south.  Only the first generation in the spring can cause economic damage to field corn. 

Late planted corn and heavy weed pressure at planting are the number one factors for a potential cutworm outbreak.   Often times the larvae are present in the foliage when a late tillage or chemical application happens prior to planting, leaving a cutworm population with nothing to feed on except the newly planted corn. 

The general University threshold for Black Cutworm  is three to five percent of plants showing damage and two or more larvae 4th to 6th instar are found per 100 plants.  However with considerably higher corn prices there has been the question of whether or not to lower the threshold to one to two percent plant damage.

Controlling Black Cutworms

Over the last several years the advancement of genetically modified traits into hybrid seed corn and the use of seed treatments have done a good job of lowering  risk of cutworm damage.  However, the cutworm has to eat the plant tissue to take up any of the insecticide provided by the seed treatment or trait.  Therefore a large population of cutworms could cause economic damage before they all die.  

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