Managing Corn Leaf Aphids During Harvest Season

By Blake Jackson

As harvest approaches, many corn growers are noticing substantial infestations of corn leaf aphids in their fields. Numerous farmers have reached out to Penn State Extension seeking guidance on the risks posed by these aphids and whether immediate insecticide applications are necessary.

At this stage of the season, particularly in September, there is little that can be done to control existing infestations. However, understanding how these outbreaks develop can help prevent similar problems in future seasons.

Corn leaf aphids are naturally present in most corn fields by June and July, but they often go unnoticed because populations remain small. Their reproductive potential is high, yet natural predators such as lady beetles and other predaceous insects typically keep populations under control, especially during pollen shed.

A common practice among growers is to apply fungicides during tasseling or silking to protect against mid-season diseases. Many also choose to add an insecticide to these applications, reasoning that “we’re already going over the field, so we might as well control insects,” often at minimal additional cost per acre. While this seems practical, it can inadvertently trigger aphid outbreaks.

Tank-mixed insecticides frequently eliminate beneficial insects rather than aphids, removing the natural checks on aphid populations. With predators suppressed, aphids can multiply rapidly, creating large infestations that may reduce yield if they emerge early in the season.

The most effective approach to pest management remains Integrated Pest Management (IPM). IPM emphasizes applying insecticides only when economic thresholds are exceeded, ensuring that treatment provides a tangible economic benefit. Scouting fields regularly is essential to determine whether pest populations justify action.

Avoid automatically adding insecticides to fungicide sprays. Instead, monitor your fields carefully, apply insecticides only when pest populations surpass thresholds, and allow natural predators to manage pests when possible. By following these principles, growers can protect yield, reduce unnecessary chemical use, and help prevent future aphid outbreaks.

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