Black grass bugs are likely to blame. Black grass bugs are native to western Nebraska and feed primarily on introduced wheatgrasses, although they can feed on other grasses and broadleaf plants. Crested wheatgrass is exceptionally susceptible, especially monocultures that provide the opportunity for substantial population growth.
Feeding damage often causes a significant reduction of forage production, especially during dry years. Damage occurs when the insect consumes cells within the leave, including chlorophyll which gives the leaf its green color and absorbs energy from the sun for photosynthesis. As a result, the cells lose their color causing the entire leaf and often a large area to appear white. With enough damage, plants can lose their ability to recover causing the plant to go dormant or die.
When grass growth begins in the spring, black grass bug eggs hatch and the juveniles begin feeding. Juveniles mature over 4 to 5 weeks and live for several more weeks as adults. Adults can be up to 1/4 inch in length and can be completely black or black over most of the body with some tan coloring along the outer wings. Immature stages are similar in appearance to the adults, but smaller and may appear grayish. In June after mating, female black grass bugs lay eggs in “grass straws,” dried out (not green), solid, standing hollow plant stems, where they remain until hatching in the spring. Black grass bug eggs only hatch in the spring resulting in one generation per year.
Damaged plants are easier to find than immature black grass bugs that are small, feed at night, and spend the day near the soil surface. Areas at highest risk are those that had infestations the previous year. Begin monitoring for plant damage when grass growth beings. Black grass bugs infest a field from the edges from neighboring areas or road ditches.
If not managed, black grass bug populations tend to increase annually. Thankfully, because black grass bugs only have one generation each year and they are not highly mobile, control is highly effective, especially before the population peaks in mid-May, and is often not necessary each year (although monitoring annually is recommended). However, no well-researched economic thresholds exist for managing black grass bugs making it difficult to know when treatment is necessary.
Insecticides are effective at controlling adult bugs in the spring but have no effect on eggs. Damaged areas should be surveyed prior to spraying to ensure adults are actively feeding prior to laying eggs June. After eggs are laid, reduction of dried grass straws by grazing, moving, or burning will reduce egg survivability. Grazing forage regrowth after haying or feeding livestock on hay fields can help reduce black grass bug populations the following spring.
With adequate moisture, damaged plants have a good chance at recovering after black grass bugs are removed. Survey damaged areas for active feeding and considering using insecticide to kill black grass bugs before they cause more damage and before they lay eggs.