Corn: Leaf Aphids

Excerpt from Agronomy Guide for Field Crops (Chapter 3)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Description
2. Life History
3. Damage
4. Scouting Technique
5. Action Threshold
6. Management Strategies
7. Updates on Corn: Leaf Aphids
8. Related links...

Description

These aphids are small (2mm or less), bluish green, soft-bodied insects with black legs and short black cornicles ("tailpipes") near the rear of the abdomen. They have piercing and sucking mouthparts and feed on the juices (nutrients) of young plant tissue (tassel and whorl). They secrete a sticky substance referred to as "honeydew," which can become coated with a blotchy, sooty mould.

Plate 23. Corn leaf aphids clustered on corn ear. Tassels and silks may become coated with honeydew, reducing pollination success.

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Life History

This pest does not overwinter in Ontario but instead is carried each year by air currents from the south where crops are more advanced. Initial spring migrants feed on winter barley, until corn becomes attractive. Migrating populations are comprised of winged females only. Once they settle, these females reproduce without mating and give birth to live wingless nymphs. Both winged and wingless adults are produced, depending on the nutrient quality of the plant. Winged aphids then fly to nearby corn fields and enter the whorl. There are several generations per year.

Damage

The degree of feeding injury depends on the size of the population. Nymphs and adults feed primarily on the whorls of the plant, removing nutrients and water. Symptoms include yellowing, wilting and curling of the leaves. During drought conditions, symptoms may be amplified. As densities increase, leaf surfaces and tassels often become black and sooty as mould begins to grow on the honeydew. Tassels may become gummy, causing poor pollination. They also may vector maize dwarf mosaic virus and barley yellow dwarf virus.

Scouting Technique

Examine five sets of 20 plants per field.

Action Threshold

If 50% of all plants during late-whorl to early tassel have 400 aphids per plant, and plants are under drought stress, control is required.

Management Strategies

Chemical control is warranted only if the natural enemies and parasites of the corn leaf aphids are not present and aphid densities are above their economic thresholds. There are several biological control agents that exist and are quite effective. These include ladybird beetle adults and larvae, lacewing adults and larvae, and a few parasitic wasps.

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Updates on Corn: Leaf Aphids

• Field Crop Protection Guide - Publication 812
  • Corn: Corn Leaf Aphid

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Related links...

• Insects
• Corn

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