Corn Leaf Aphids

Corn Leaf Aphids on corn plant. The discolored aphids are parasitized.

Corn Leaf Aphids are not as detrimental to yield in corn fields as aphids are in soybean fields. The biggest loss to yield is when corn leaf aphids start feeding on the top portion of leaves and the tassel before pollination starts. After pollination, there is very little effect on yield from damage caused by corn leaf aphids. If corn plants are under stress after pollination, this is when the damage from corn leaf aphids will affect yield. Knowing how to scout for corn leaf aphids is necessary in order to know your economical threshold and figure out if it is necessary to spray.

Pre-pollination scouting

During pre-pollination scouting, check 20 plants at random in 5 areas of the field (4 plants in each area). While scouting for corn leaf aphids, if any of the following items are true, then spraying is recommended.

• If more than 50% of the scouted plants have 100 aphids or more.
• If the aphids are on the upper portion of the plant and tassels are covered or if there are 15 aphids down in the whorl and third, if the tassel is covered by a sticky substance from the aphid infestation spraying is recommended.

Post-pollination scouting

While conducting post-pollination scouting, check 20 plants at random in 5 areas of the field (4 plants in each area). Again, while post-pollination scouting for corn leaf aphids, if any of the following statements are true, then spraying is again recommended.

Lady beetle attacking aphids

• If more than 50% of the scouted plants have 100 aphids or more on them and the plant is stressed.
• If there are 100 aphids or more and the plant is not stressed, look at the beneficial insects in the field, this being lady beetles and green lacewings.

If there is a presence of beneficial insects in the field then wait two days to re-scout the field since in the later part of the season aphids will die off quickly. After the second scouting, if there is still a heavy presence of aphids, spraying is recommended to prevent yield loss.