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.
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.
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.
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.