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As corn begins to emerge, it is important to scout it frequently for damage from a variety of insect pests. This is true regardless of whether it was treated with an insecticide at planting time (liquid, granular or seed treatment) or whether it is a Bt corn hybrid.
High populations of insects may overwhelm the protection provided by these controls, and in some cases products are not labeled for the full spectrum of insects we may encounter in Nebraska.
Some early season insects to watch for include various cutworm species, and, in southeast Nebraska, the southern corn leaf beetle. Cutworms can cause serious damage to corn in the first couple weeks after emergence, so it is important to scout fields for damage. Several species of cutworms attack corn. The severity and the area affected will vary greatly, depending on species involved, previous crop history, and weather conditions. See the March 10, 2006 Crop Watch for a complete discussion of corn cutworm management.
Scouting and rescue treatments
Remember that early detection of a problem is essential because most of the cutting occurs within seven days of plant emergence. Generally, a rescue treatment should be considered if cutting is observed on 5% or more of the plants (an average of at least 1 plant in 20) and the worms are one inch or less in length. Rescue treatments are effective in controlling soil cutworms. Ambush 2E, Asana XL, Baythroid, Lorsban 4E, Mustang Max, Warrior, Proaxis, and Pounce 3.2EC (or generics) all will give satisfactory control as post-emergence sprays. If the soil is dry or crusted, rotary hoeing immediately before or after Lorsban application may enhance control. The other insecticides are pyrethroids and should not be incorporated.
See a full list of products and rates on the Department of Entomology Web site. For more information on managing this pest, see the University of Nebraska Cooperative Extension NebGuide, Corn Cutworms (G1153).
Southern corn leaf beetles
A relatively new pest of corn - the southern corn leaf beetle – has caused damage periodically in southeast Nebraska since 2000. This insect has been reported to damage corn in northeast and north central Kansas over the last few years, and also has been reported in Missouri, Iowa and Illinois.
The adult overwinters in sheltered areas and becomes active in April. In addition to corn it may feed on weeds, especially cocklebur. The adults are 3/16 inch long, dark brown and often covered with soil particles, making them difficult to see. They hide in the soil during the day and are difficult to find. They feed on the stems of corn seedlings and may cut stems, causing damage similar to cutworms on seedling corn. They also feed on the edges of leaves, producing a notched appearance, similar to leaf feeding by cutworms. If abundant they may severely damage seedling corn.
Economic thresholds have not been researched for this insect, but use of thresholds similar to those for cutworms has been suggested. The same insecticides labeled for post-emergence use against cutworms would be appropriate for southern corn leaf beetles.
Robert Wright
Extension Entomologist
Keith Jarvi, Extension Assistant
Integrated Pest Management
Northeast REC
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