Billbugs are early season pests that feed on corn. Signs of billbug damage in you corn fields include: tillering, leaf wilting, or a line of holes on leaf surfaces. Management practices that promote seedling growth and vigor can help protect your field against the incidence of billbugs.
What to Watch For:
Billbugs are weevils with a pronounced snout or beak that can cause early season damage in corn. The two main species that feed on corn are the maize billbug and the southern corn billbug (SCB). Maize billbug can be found throughout corn growing regions of the United States and is reddish-brown to black, ranging in size from 3/8 to 1/2 inch long (Figure 1). Southern corn billbug can be found throughout the south, and up the Missouri River valley into the Midwest. They are 1/3 to 1/2 inch long, ash gray or brownish in color and usually covered with soil and dust.
Billbugs overwinter as adults in the soil or plant litter and become active as corn begins to emerge. Billbugs will feed on other grasses, most notably yellow nutsedge. They feed at night and are rarely seen; however, SCB can sometimes be found attached upside down to a corn seedling near the soil line. Adults lay eggs in the plant stem, hatching within 4 to 15 days depending on temperature. White grubs feed and develop for several weeks in the center of the corn stalk, later moving into the soil to feed around the stem and roots. There is one generation per year.
Impact on Your Crop
Billbugs cause damage to young corn plants by feeding on the tender inner tissue of the stalk. Small plants can be severely injured or killed if feeding occurs on the growing point. In larger plants, damage can be seen as a line of holes across corn leaves as they unfold, indicating where the billbug punctured the stem to feed (Figure 2).
Other symptoms of early billbug injury include tillering, stunted growth, or wilting in the center of the whorl. Adult billbug feeding begins to decline around the 6- to 8-leaf stage in corn. However, the grubs can continue to cause damage by feeding within the stem and around the roots. Severe feeding can cause plant lodging and small ear size.
Tips to Manage
Managing billbugs in corn require an integrative and preventative approach. High-risk fields, such as fields with a history of billbugs or yellow nutsedge, should be scouted for billbug damage from corn emergence through the 6- to 8-leaf stage.
Scouting for billbugs in corn:
- Walk a zig-zag pattern across the field looking for insect damage or poor stands.
- If found, dig up several plants to verify insect damage.
- If insect damage is confirmed, examine 100 plants in the area and record the number of damaged plants. Continue sampling throughout the field.
The economic threshold for billbugs is 5% seedling loss.1 Plants with leaf feeding will typically outgrow and recover from the damage. Control of billbug is only needed when damage is reducing stands to critical levels. No rescue treatment is available for larvae feeding inside of corn stalks.
Management practices that help reduce billbug populations include: controlling yellow nutsedge, crop rotation, early corn planting, or the use of a seed-applied or soil-applied insecticide. Agronomic practices that promote rapid early-season growth will also help in managing billbug infestations. Over-the-top insecticide rescue treatments are ineffective since infestations are generally identified after damage occurs.
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1Van Dyn, J. 2004. Management of southern corn billbug in field corn. North Carolina State University.
2 Purdue Extension Entomology. 2009. Maize billbug - Purdue Fields Crops IPM 2009. Purdue University.
3 Reisig, D. 2015. 6 things to consider about billbug management. North Carolina Cooperative Extension. http://agfax.com.
Web sources verified 02/08/18 15100910365