Illinois Field Crop Applicators Practice Test

What pest causes yellowish leaflets and dark brown triangular leaflet tips?

1. Potato leafhopper

2. Alfalfa weevil

3. Flea beetle

4. Corn rootworm

The correct answer is: Potato leafhopper

The yellowing of leaflets combined with dark brown triangular tips is a characteristic symptom of damage caused by the potato leafhopper. This pest is known to feed on a variety of crops, particularly alfalfa and other legumes, where its feeding activity leads to a condition known as "hopper burn." The pest removes sap from the plant, and this sap removal leads to the discoloration of the leaflets, particularly at the tips. The yellowing occurs as the plant struggles to cope with the stress of feeding and possibly due to the loss of nutrients necessary for healthy foliage. The triangular shape of the dark tips can correspond to the pattern of feeding and the specific way the potato leafhopper causes damage to the plant tissue. Other pests listed, such as the alfalfa weevil, can also cause leaf damage but typically exhibit different symptoms, such as the skeletonization of leaves rather than the specific yellowing and browning pattern associated with potato leafhoppers. Flea beetles and corn rootworms have distinct damage symptoms, primarily characterized by small holes in leaves or root damage, respectively, which do not match the described symptoms as closely.