The tiny, brown, southern corn leaf beetle feeds on the whorls of corn seedlings as they begin to emerge, potentially destroying the plants down to the soil line.
In most years, the southern corn leaf beetle (Myochrous cyphus-denticollis spp.) is not typically an economically significant pest. Yet, this rare insect pest possesses the ability to severely damage a corn crop unless preventive measures are taken. That’s why farmers may want to keep it on their checklist of insect pests to proactively manage.
Research history from Kansas State University documents that the southern corn leaf beetle devastated a large portion of cornfields in the northeastern part of the state in the late 1990s. Until that incident, it had been 80 years since the southern corn leaf beetle was reported to damage corn fields.
Identification and Lifecycle
Adult southern corn leaf beetles are tiny – only 3/16 inch to 1/5 inches long – and brown in color. Southern corn leaf beetles deposit up to 50 eggs at the base of a corn plant or in crop residue. Larvae hatch within 10 days and feed on corn roots or weeds such as crabgrass. Larvae mature in 10 weeks and emerge from the soil as adult beetles, when they can begin to fly from field to field.
As seedlings begin to emerge, the beetles will begin to feed in the corn whorl, and the corn plant will bend down.
The southern corn leaf beetle overwinters in crop residue and under the soil. This insect can produce up to four generations per growing season. In the Central Corn Belt, the southern corn beetle larval stage typically occurs during mid-May through mid-June, depending on geography.
Heavy infestations of southern corn beetle can damage corn plants so extensively that they die. This pest can destroy corn seedlings down to the soil. In fact, even a healthy stand of corn can be destroyed when a large population of this insect lands in a field.
Begin scouting for southern corn leaf beetles as soon as seedlings emerge. A sign to note is that beetles easily fall to the ground when corn leaves are brushed by human movement through a field, but they are difficult to see because of their small size. A hand lens is helpful. Refer to a pest identification guide to avoid mistaking southern corn leaf beetle damage for cutworm or armyworm feeding. Follow University Extension weekly and monthly reports for scouting guidelines and economic thresholds for insecticide treatments in specific corn-growing geographies.
Southern Corn Leaf Beetle Management Options
In no-till or limited-till situations, southern corn leaf beetle may become established in the soil, overwinter and feed on newly planted seedlings. For best results managing southern corn leaf beetle, remove existing crop residue and control weeds through tillage, a burndown herbicide and residual preplant herbicides.
Taking out existing vegetation prior to planting will also provide better penetration of insecticide spray or granules. Season-long weed control helps prevent southern corn leaf beetle from causing crop damage and harming yields and will help improve effectiveness of in-season insecticide treatments. Additionally, crop rotation continues to be one of the most economical and effective cultural practices for controlling a wide range of crop pests.
Farmers should consult with their seed dealer and review University Extension field trials to evaluate corn hybrid options and traits to help control southern corn leaf beetle. Although there is no trait that controls southern corn leaf beetle, using hybrids that will help control other insect pests can decrease your odds of misidentifying another pest as responsible for feeding damage if southern corn leaf beetle is the true culprit.
The best approach to managing southern corn leaf beetle is prevention.
While this insect may not be a significant pest every year, when a severe infestation does occur – and it can – farmers need to be ready. Seed treatment is a good risk management measure. Under low to moderate southern corn leaf beetle pressure, there are insecticide seed treatments labeled to protect against this pest.
Under heavy beetle pressure, seed treatments may not offer enough protection. That’s when good scouting will help to make the decision if an insecticide treatment may be warranted.
Baythroid® XL insecticide, a pyrethroid, performs on a broad spectrum of corn insect pests, with fast knockdown and long residual control. At-planting application is recommended; however, Baythroid XL can be used all season long. Application timing should be based on careful scouting and local economic thresholds. Follow IPM guidelines to effectively use postemergence insecticides as needed and manage insecticide resistance in combination with other control practices.
To learn more about insect control options in corn, including Baythroid XL, contact your local Bayer representative.
*Always read and follow label instructions. Not all products are registered for use in every state. Baythroid XL is a Restricted Use Pesticide.