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Understand aphid effects on yield

Agronomy Bulletin 118 - Corn Aphids

Bird cherry-oat aphids are yellow-green or dark green in color and have round bodies. Image courtesy of Adam Sisson, Iowa State University, Bugwood.org

Situation

Corn aphids are becoming a common pest for corn growers, as populations can develop in massive numbers. Aphids are problematic during tasseling and can colonize corn later in the summer, with populations building to striking levels, threatening yield potential.

Factors to Consider

  • Aphid species
  • Plant damage
  • Monitoring corn
  • Tassel emergence
  • Management and treatment
  • Economic loss
a heavily infested corn leaf, image courtesy of Frank Pealrs, Colorado State University, Bugwood.org

Action Plan

  1. Spot aphid damage. Corn leaf and bird cherry-oat aphids are two aphid species typically found in corn. They are similar in size and color, though cherry-oat aphids have an orange-red saddle between the cornicles. All species cause the same damage in fields. Heavily infested plants are discolored and stunted with wilted, curled or yellowed leaves and, sometimes, shriveled ears. Aphids feed on the sap from the plant phloem. They excrete sugar-rich honeydew that covers the plant and can interrupt both plant growth and pollination. Excessive feeding within the whorl before tassel emergence leads to incomplete kernel development or barren ears.
  2. Scout multiple locations. Start scouting for aphids three weeks before tasseling. Check five locations within the field and examine 20 plants at each location. Aphids colonize deep within the whorl. Examine the ear, leaves and stalk. Take note of beneficial insects, such as ladybugs, and parasitized mummies. Consider not treating aphids if more than 20 percent are parasitized.
  3. Control before tassel emergence. Feeding by large aphid populations can significantly cost yield. Protect yield by controlling aphids two to three weeks before tassels emerge. When aphids are deep in the whorl, spraying is not effective. When aphids exceed thresholds, spray when they are outside the whorl or on the tassel. Corn plants also can be sensitive to aphid feeding if they are drought-stressed. Treat plants if 50 percent of the plants are infested with colonies of over 75 aphids per plant.
  4. Late-season management. Although control is not typically required once tassels emerge, treatment is needed if aphids interfere with pollination. Treat aphids if more than 50 percent of the tassels are covered with aphids and their honeydew and before pollination is halfway complete.

Summary

Corn aphids are found in corn throughout the growing season. Although corn aphids are not new during pollination, post-pollination corn aphids are relatively new — thus the economic threshold levels are still unclear. It is important to understand the damage aphids cause to determine if management is needed.

For more information, contact your local Mycogen Seeds customer agronomist or trusted agronomic adviser.

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Published on Thursday, August 07, 2014