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Longhorned beetles pose stalk lodging threat.

Agronomy Bulletin 94 ─ Longhorned Beetles in Sunflowers

Longhorned beetle adults typically emerge in mid-June.

Situation

Historically, sunflower stem weevils have mostly caused sunflower stalk lodging damage. However, in recent years the longhorned beetle also has become a concern. Growers who can identify the problem can escape the financial penalty.

Factors to Consider

  • Identification
  • Life cycle
  • Lodging damage
  • Management options
If longhorned beetle larvae are lodging the stalks of your sunflower crop, consider early harvest.

Action Plan

  1. Identify the opponent. Bluish gray in color, adult longhorned beetles are about ½ inch long. In daylight, the pest can be found under the leaves within the plant canopy, flying or loitering on exposed plant surfaces. Longhorned beetle also is referred to as Dectes texanus, Dectes stem borer, sunflower stem girdler and soybean stem borer. Soybean, cocklebur and ragweed plants also are common hosts of the longhorned beetle.
  2. Consider life cycle. One generation of adult longhorned beetles surfaces per year, beginning in the High Plains around mid-June to early July. A week after emergence, females become reproductively active, laying eggs into the leaf petiole (leaf stalk). Once hatched, the larvae invade the stalk to feed. Eventually, mature larvae overwinter at the base of the plant stalk, increasing the risk of lodging. Lodging is most likely in higher high plant populations with 10 percent seed moisture. Note that longhorned beetle damage is often misidentified as sunflower weevil damage.
  3. Understand management options. Fortunately — unless infected plants lodge — longhorned beetles carry minimal economic consequence. In late summer, examine fields by splitting stalks. If infested, harvest early. Delaying planting until after June 1 may help, but longhorned beetles can pester plants deep into the season. Further, insecticides have not been proven to control the longhorned beetle.

Summary

Even with limited options to control longhorned beetles, sunflower growers can still produce a profitable crop. If you have any concerns about whether your crop is infested and needs an early harvest, contact your local Mycogen Seeds customer agronomist or trusted agronomic adviser.

Published on Tuesday, July 30, 2013