Black Grass Bugs

Order: Hemiptera
Family: Miridae

Description

Black grass bugs belong to the order Hemiptera and have piercing-sucking mouthparts. 

Mature black grass bugs are about 6.5 mm (¼ inch) long. Adults of L. hesperius have a lighter band on the outer fringe of the wing covers, while adults of I. brachycera are completely black. Females tend to lack fully formed wings, which limits their ability to disperse to new areas. If wings are present the front wings are partially sclerotized.

Immature stages are smaller than adults but similar in appearance.

Quick Facts

• Two species of black grass bug are considered turfgrass pests in Colorado, Lapobs hesperius Uhler and Irbisia brachycera Uhler.
• Black grass bugs have a wide host range. While they prefer feeding on grasses, they can also feed on broadleaf plants when grasses are not available.
• Monitoring black grass bugs in the spring is recommended for effective treatment.
• Feeding injury of black grass bugs is more severe when plants are drought stressed, and when densities of black grass bugs and other pests are high.

adult L. hesperius

Adult Labops hesperius. Note the light coloration on the outer fringe of the wing covers.
Whitney Cranshaw, Colorado State University, Bugwood.org

There are two species of black grass bug that are pests of turfgrass in Colorado, Labops hesperius Uhler and Irbisia brachycera Uhler. These insects are considered pests of wheatgrass, but they can also attack turfgrass. Cultural control is usually sufficient in managing black grass bug densities.

Black grass bug in CO

Black grass bug (Irbisia sp.) on grass in Colorado
Frank Peairs, Colorado State University, Bugwood.org

adult bed bug

Stippling injury caused by feeding of black grass bugs.
Whitney Cranshaw, Colorado State University, Bugwood.org

Life Cycle

Black grass bugs overwinter as eggs in the stems of grasses. The eggs hatch when grasses begin to grow in the spring; however, the timing of egg hatch is highly dependent on temperature. Egg hatch occurs earlier at higher temperatures and later at lower temperatures. After egg hatch, it typically takes around four or five weeks before adults begin to appear, and a single generation is produced each year. Nymphs develop through five instars before reaching adulthood.

Injury

Feeding injury of black grass bugs is typically limited to the edges of fields. Black grass bugs feed on plant fluids with piercing-sucking mouthparts, and they tend to feed on the upper surface of leaves. Within seconds after feeding begins, a white spot starts to form at the feeding site. Feeding of black grass bugs can cause leaves to appear straw-colored, a symptom that is visually comparable to frost damage.

Monitoring

Grass should be inspected for areas of discoloration, especially stippling injury. A sweep net can be used to sample plants for black grass bugs since they tend to drop to the soil when disturbed.

Cultural Control

Mowing can help reduce the number of black grass bug eggs and providing lawns with adequate moisture can help plants recover from feeding injury.

Chemical Control

Annual management with insecticides is typically not necessary since black grass bug populations take several years to grow to damaging densities. Furthermore, the cultural control recommendations described above tend to be sufficient in managing black grass bugs. However, in lawns previously impacted by black grass bugs, applying certain insecticides during spring emergence can be effective. The insecticides kill adults but do not have any effect on eggs within grass stems, and if enough eggs are present then reinfestation may occur the following year. For more information on chemical management of black grass bugs, consult the Pacific Northwest pest management handbook.

References

Hammon, R. W., and Peairs, F. B. (n.d.) Black Grass Bugs. Colorado State University – Extension. Available https://extension.colostate.edu/topic-areas/insects/black-grass-bugs-5-575/
Pacific Northwest Pest Management Handbook. (n.d.). Rangeland-Black Grass Bug. Available https://pnwhandbooks.org/insect/hay-pasture/rangeland/rangeland-black-grass-bug
Wagner, P. 2020. Be on the Lookout for Black Grass Bugs. South Dakota State University – Extension. Available https://extension.sdstate.edu/be-lookout-black-grass-bugs