By Blake Jackson
As corn crops approach maturity, many growers begin planning fungicide applications to protect yield and plant health. During this process, some farmers or custom applicators also recommend adding an insecticide to the spray tank, arguing that since the equipment is already crossing the field, it makes sense to control insects at the same time.
While this approach may seem economical because adding a pyrethroid insecticide costs only a few dollars per acre, Penn State Extension entomologist John Tooker says the practice can do more harm than good.
One of the clearest examples involves corn leaf aphids. Although many corn fields naturally contain small aphid populations, these insects rarely reach damaging levels because beneficial predators such as lady beetles, their larvae, and predatory bugs keep them under control.
Applying an insecticide when pest numbers are already below economic thresholds can disrupt this natural balance.
In many cases, the insecticide does not eliminate every aphid, but it significantly reduces the population of beneficial insects that feed on them. Without these natural predators, the surviving aphids can multiply rapidly, creating large infestations that may become far more severe than the original population.
According to Tooker, unusually high corn leaf aphid outbreaks are often linked to unnecessary insecticide applications rather than natural population growth.
To avoid this situation, growers should continue following the principles of Integrated Pest Management (IPM). This approach recommends using insecticides only when field scouting confirms that pest populations have exceeded established economic thresholds. These thresholds are designed to indicate when the financial benefits of treatment outweigh the costs.
Regular field scouting remains the most reliable way to determine whether insect control is truly needed. If insect populations exceed recommended thresholds, an insecticide application is justified.
However, if pest levels remain below those thresholds, skipping the insecticide helps preserve beneficial insects, reduces unnecessary pesticide use, and supports a healthier, more balanced crop environment while avoiding avoidable input costs.
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Categories: Pennsylvania, Crops, Corn