Illinois Field Crop Applicators Practice Test

Which pest is responsible for causing irregular emergence in corn plants?

1. European corn borer

2. Japanese beetle grubs

3. Leaf aphids

4. Black cutworms

The correct answer is: Japanese beetle grubs

Japanese beetle grubs are known to affect the root system of plants, including corn. They feed on the roots, which can compromise the plant’s ability to uptake water and nutrients. When roots are damaged, it can lead to a lack of stability and health for the corn, resulting in irregular emergence. This happens because the young corn plants may not have a sufficient root mass to support their growth or may even become stressed or stunted, leading to uneven or poor emergence above ground. Other pests mentioned have different direct impacts on the corn. For instance, the European corn borer primarily attacks the stalks and leaves, which can result in damage later in the plant's growth but is not directly linked to emergence issues. Leaf aphids are sap-sucking insects that can weaken plants over time but typically do not affect emergence. Black cutworms tend to cut down young plants at or below the soil line, impacting their survival afterward rather than causing irregular emergence.