Low Black Cutworm Numbers and Increasing Bird Damage

Published: May 19, 2011

Although several calls have been received concerning black cutworm cutting damage, the overall problems in fields have been less than expected. Typically, in most years there is a strong correlation between moths captured and the number of black cutworm infestations that follow. However to date, the 2011 season has shown the correlation to be less than impressive. It illustrates that many factors can influence moth egg laying and subsequent larval survival to the 4th instar, when seedling corn plants are initially cut. Windy conditions, types of field crop residues, the presence of winter annual weeds, the effectiveness of beneficial agents, and many other factors may all impact egg laying and larval survivorship. Some corn fields receiving damage from black cutworm larvae this spring may actually be fields where seedling corn plants were clipped by blackbirds and grackles. Over the past ten years, populations of various blackbird and grackle species have increased according to federal fish and wildlife surveys. These population increases have resulted in greater damage to corn and rice crops throughout many Southern and Midwestern states, including Missouri. In 2011, a Section 18 request from Missouri was submitted for the avian repellent Avipel for use as a seed treatment on field corn in Missouri. It was rejected by EPA, who requested that additional information be included in the package if re-submission was planned for 2012. At present, a team of state extension specialists are reviewing the EPA rejection letter to determine the type and availability of the information requested. Once determined, a revised Section 18 package will be submitted for use in 2012.

To date, many complaints of bird damage have been received. In addition, It is believed that a portion of the damage to seedling corn reported to be caused by black cutworm larvae may have been misdiagnosed. This is because it is often difficult to tell black cutworm cutting from blackbird clipping in seedling plants. When black cutworms cut plants, they often try to drag the plant stem and foliage beneath the soil surface to feed. In contrast, blackbirds will often walk down a corn row as they grab seedling and try to pull them out of the ground. Often the corn seedling will break near where the beak makes contact with the seedling, resulting in a plant stem and foliage appearing as if it has been cut. Usually the bird will drop the clip seedling if it breaks and continue moving down the row to pull on another plant in order to collect the seed. Often, birds will also pull soil from around the base of the plant in an attempt to reach the seed. This results in a cone-shaped hole surrounding the plant seedling.

Hopefully a section 18 Avipel package will be accepted by EPA in latter part of this year for use in 2012. Information will be passed along to growers as the process of submission moves forward.