Muhly grass (Muhlenbergia capillaris)*, sometimes known as sweetgrass, is a beautiful ornamental grass celebrated for its displays of pink, purple, or white flowers in the late summer and fall.
Pink muhly grass popular ornamental grass because of their wispy floral displays and durability in the landscape.
S. Cory Tanner, ©2018, Clemson Extension
‘White Cloud’ muhly grass also a popular ornamental grasses because of their wispy floral displays and durability in the landscape
S. Cory Tanner, ©2018, Clemson Extension
Native to the coastal plain from Connecticut to Texas, this perennial, clump-forming grass is a tough and reliable landscape plant in the Southeast. As a result, it has become very popular in South Carolina landscapes. Additionally, wild muhly grass is one of the primary components of the famed sweetgrass baskets of the SC Lowcountry.
Muhly grass is generally pest and disease free, making it a low-maintenance perennial, but an insect pest was recently discovered for the first time in SC. The ‘muhlygrass mealybug,’ as we call it, doesn’t have an official common name. Its scientific name is Stemmatomerinx acircula. It was identified from a home landscape planting of muhly grass in the West Ashley area of Charleston County in Fall 2018. According to the USDA, this was the first report of the insect outside of Florida, where it is native.
Muhly grass infested with muhlygrass mealybug (Stemmatomerinx acircula).
Merle Shepard, ©2018, Clemson University
Closeup of a muhlygrass mealybug (Stemmatomerinx acircula) on a leaf blade.
Merle Shepard, ©2018, Clemson University
Large infestations of muhlygrass mealybugs are very noticeable and visually unattractive in the landscape. Besides this aesthetic damage, mealybugs feed on leaf sap from the grasses, reducing infested plants’ health and vigor. In severe cases, fall flower production, the primary ornamental feature of muhly grass, may be delayed or entirely lacking.
Muhlygrass mealybugs reach approximately 1/8 inch long and are roughly twice as long as wide. Nymphs and adults are covered with short, dense wax filaments with many long, slender filaments that can be double their body length. The wax and filaments are bright white and give individuals a “hairy” appearance, similar to a loose cotton swab. In South Carolina, muhlygrass mealybug infestations become noticeable from late May to June and remain active until late-Fall. Active adult females lay hundreds of eggs under elongated tubular ovisacs (egg cases) along the leaves. The eggs hatch into tiny “crawlers” that disperse by walking to other leaves and nearby host plants. We think long-distance dispersal probably occurs through the movement of infested plant material. The mealybugs probably overwinter within the plant crown or roots, but this has not yet been confirmed.
Management of muhlygrass mealybugs in the landscape is the focus of ongoing research, but here are some management suggestions based on what we know so far. First, prevent infestations by inspecting new muhly grass plants for mealybugs before purchasing or installing. Remove and destroy severely infested and declining plants from the property if possible. Similarly, bag and remove clippings when pruning leaves and flowers from infested plants. For light infestations, horticultural oil or systemic insecticide applications may be effective. Follow all label instructions when applying an oil or insecticide.
Beyond the basic information above, we know very little about this insect’s biology, distribution, or pest status. Clemson University researchers are working to determine how widespread it is, if it is likely to spread farther, and if it will become a significant or occasional pest of muhly grass or other plants. The results of this research will inform future pest management decisions to maintain the use of muhly grass in the landscape.
You can help! If you see muhly grass plants with clumps of white fuzz on their leaf blades (see photos), we encourage you to complete this survey to help us document the distribution and severity of the muhlygrass mealybug.
Click to Access Muhlygrass Mealybug Survey or scan the QR code below.
Muhlygrass Mealybug Survey QR code.
* Most botanists now agree that the pink muhly grass widely planted in landscape settings is not actually Muhlenbergia capillaris but a closely related grass, Muhlenbergia sericea. We continue to use the name M. capillaris when referring to muhly grass because it is the most used in the horticulture trade.
References:
- Baker, James. 2022. Muhlygrass Mealybug. NC State Extension PDIC Factsheet. https://content.ces.ncsu.edu/muhly-grass-mealybug#
- Bolles, B. 2016. Muhly Grass Pest. UF/IFAS Extension, University of Florida. https://blogs.ifas.ufl.edu/escambiaco/2016/04/22/muhly-grass-pest/
