Alfalfa growers noticing crinkled or disfigured plants in their stands may want to put the blame on herbicide damage when it very well could be plant bugs. So says Matt Montgomery, Extension educator for University of Illinois Extension’s Fulton-Mason-Peoria-Tazewell Unit.
Two types of plant bugs, the alfalfa plant bug and the tarnished plant bug, are found in Montgomery’s area. The alfalfa plant bug is pale green, long-legged, winged and 1/8” wide and ½” long. Nymphs are smaller, green and wingless. They resemble adults except for having dark red eyes. The bugs spend the winter as eggs within the stems of alfalfa plants, hatch in spring, emerge from stems in mid-May and lay eggs in late June. Two generations follow the May emerging.
The tarnished plant bug is ¼” long, brown, stubby-shaped and mottled white and yellow. Nymphs are also green and resemble the adult except for several black spots. Tarnished plant bug adults overwinter in legume field debris, fencerows and ditch banks, emerging when the weather warms up in spring. Adults insert eggs into plant stems, leaf midribs, petioles and flowers. Three to five generations occur each year.
Both types of plant bugs have piercing, sucking mouth parts that help them remove plant juices and cause the peculiar leaf symptoms noticed in many fields. For scouting, Montgomery recommends using a 15”-wide sweep net to sweep five locations in a field and each location 20 times. For plants less than 3” tall, control is warranted when three plant bugs/sweep exist. For taller plants, control is necessary when five or more bugs per sweep are found.
Here’s an Oregon State University Extension video on how to sweep for insects.