Pest Management

“A weed is a plant that has mastered every survival skill except for learning how to grow in rows.” Wisconsin humor columnist Doug Larson

He’s right! Grassy weeds are the masters of survival, thriving in adverse conditions and dramatically outpacing the plants we want to succeed.

Here come the grassy weeds
Grassy weed seeds hide in root balls and find their way into seed packets. Wind, rain, birds, and even household pets spread the seeds across our lawns and gardens. Once rooted, grassy weeds can quickly take over, spreading their roots, stolons, and tubers. What’s a gardener to do?

Begin with identification
Grassy weeds come in all sizes and shapes. They can be annual, biennial, or perennial. And some, like sedges and rushes, aren’t really grasses at all, but are easily mistaken for grassy weeds at first glance.

Leaves and stems are the easiest way to distinguish grasses and sedges from other broadleaf weeds. Broadleaf weed leaves are usually wide and come in a variety of shapes, including round, oval, or lanceolate. Their stems are either square or round. These weeds usually have identifiable flowers—think dandelions! Grasses and sedges, on the other hand, have long, narrow leaves that generally grow upright, often in clumps. Grass stems are round or flat, while sedges have triangular-shaped stems. Try rolling a sedge stem between your fingers—you can easily feel the bumpy edges. Instead of producing typical flowers, grasses and sedges send out spikes of tiny, individual florets and scale-like bracts, respectively .

Rushes come in many varieties—some that grow in clumps with soft, grass-like foliage (soft or common rush, Juncus effusus); others that grow on hollow, stiff stems (horsetail or scouring rush, Equisetum hyemale). Although not technically considered a “weed,” we identify them here because their emerging foliage appears grass-like. Rushes are often desirable ornamental plants in a wetland or water garden, although they may aggressively spread. 

Stubborn annual grassy weeds

• Crabgrass (Digitaria). The North Carolina Extension Gardener Handbook tells us that crabgrass was one of the first grains cultivated in Europe during the Stone Age—little consolation when it’s taking over your lawn! Crabgrass germinates from March through May, encouraged by alternating wet/dry conditions in the spring. It has a prostrate growth habit, and spreads not only by seeds, but also by stolons that send down roots at each node.
• Goosegrass (Eleusine indica). This invasive weed takes hold in areas where the soil is disturbed or compacted, or where turfgrass becomes thin from mowing too low. Germination is usually two weeks behind crabgrass. Its name may have come from the belief that geese ate the grass or that various parts of the plant resemble a goose’s foot. Goosegrass has a prostrate growth habit, its foliage radiating outward from a white center like a wagon wheel. It spreads by seed and underground roots.
• Japanese stiltgrass (Microstegium vimineum). Introduced to the United States around 1918, this annual Asian exotic invasive likely arrived in packing material for fine porcelain destined for Tennessee. Looking like a small bamboo plant, Japanese stiltgrass prospers in most Eastern states, growing in sun or shade and preferring moist habitats. Producing up to 50,000 seeds per square foot that germinate in mid- to late-spring, it forms a sprawling mass of branches 1- to 3-feet high.
  

  

  

  

Pesky perennial grassy weeds

• Bermudagrass (Cynodon dactylon). Used as forage for hundreds of years, Bermudagrass first appeared as golf-course turf in the early 1900s. Off the putting green, stolons, rhizomes, and seeds aggressively spread Bermudagrass, making it hard to control in our tall fescue lawns or flowerbeds. Heat and drought tolerant Bermudagrass loves summer but goes dormant in winter.
• Johnsongrass (Sorghum halepense). Mediterranean exotic introduced in South Carolina around 1830, and named for William Johnson, who planted it as a forage crop along the Alabama River in the 1840s. Many consider Johnsongrass one of the 10 worst weeds in the world (Holm, Pluncknett, Pancho, and Herberger’s The World’s Worst Weeds: Distribution and Biology). It can grow over 6-feet tall in pastures and roadsides, spreading by surface rhizomes and purple panicle seed heads.
• Nimblewill (Muhlenbergia schreberi). A native grass easily confused with Bermudagrass. It forms a very dense mat in shaded, damp areas and in forest openings. Each spike-like panicle contains a single seed with a long bristle. 

  

  

  

Take quick action to control
All weedy grasses reproduce at an astonishing rate. Use Integrated Pest Management (IPM) to control the invaders and follow these tips:

• Properly water and fertilize your landscape.
• Mulch non-turf garden areas.
• Hand-pull weeds when they are young.
• Mow turfgrass to the correct height.
• Do not let weeds go to seed.

If you use herbicides:

• Apply pre-emergents according to the label at right time of year to prevent seed germination.
• Spot treat with a non-selective herbicide, being careful not to let the chemical drift onto other plants or turfgrass. 

Article written by Janet Moore, Extension Master Gardener^SM Volunteer. 

Learn more
Time to Maintain: Stop Crabgrass Before It Starts
Buncombe County Extension Master Gardener blog, March 2017

NCSU Turfgrass Environmental Research and Education
Describes differences in broadleaf weeds, grasses, and sedges. Provides descriptions and photos of grassy weeds. Offers checklist of characteristics to search for an unknown weed.

University of California Integrated Pest Management
Provides good list of grasses and sedges with photos & descriptions.