Dealing with weeds in a garden or yard can be challenging. Tall weeds with thin leaves, in particular, present an even more significant challenge.
The plant structure (height and leaf form) allows the weeds to get more sunlight, conserve water, and conduct a quick gaseous exchange for photosynthetic activity, allowing for rapid and aggressive growth.
This article will help you identify the most common weeds with thin leaves and provide the best control methods to keep them away.
1. Prickly Sowthistle (Sonchus asper)
- Family: Asteraceae
- Annual or Perennial: Annual
Common sowthistle is a tall herbaceous plant that can reach 2m in height. It produces green to bluish-green leaves about 7 to 15 cm wide and 15 to 25 cm long.
The leaves are initially produced as a rosette at the base but turn lanceolate and less lobed up the stem. They are alternately arranged with wavy, spiny margins.
The weed produces clusters of yellow flat-topped flower heads about 2.5 cm on the end of the stems.
It is native to:
- Euroasia
- North Africa
Removal methods
- Pulling: Hand-pulling before flowering or using a shovel to remove the roots can help control the weeds.
- Mechanical methods: Mowing and tillage to reduce seed production and root reserves are excellent removal methods.
- Herbicides: Apply a post-emergence herbicide like Roundup to young and actively growing plants.
2. Yellow Foxtail (Setaria pumila)
- Family: Poaceae
- Annual or Perennial: Annual
Yellow foxtail is an annual weed that can reach up to 2m in height. It produces thin, flat leaves that are bluish-green in color, about 2 cm wide, and 15 to 30 cm long.
The leaves are alternate and linear, although they may also be spirally twisted. Parts of the upper surface near the base are covered with long, sparse hairs.
The weed produces distinct stiff yellow bristles that produce yellowish-brown ovoid seeds about 3mm long.
It is native to:
- Europe
- Asia
Removal methods
- Pulling: Pulling or digging with a trowel is effective for small infestations.
- Lawn Fertilization: Maintain a healthy lawn through timely fertilization and irrigation during drought.
- Herbicides: In spring, apply a pre-emergent herbicide like prodiamine, pendimethalin, or dithiopyr. Post-emergence herbicides indicated for yellow foxtail include quinclorac, topramezone, and fenoxaprop-p-ethyl products.
3. Barnyard Grass (Echinochloa crus-galli)
- Family: Poaceae
- Annual or Perennial: Annual
Barnyard grass is a tall annual grass that grows up to 1.5m in height. It produces pale green leaves about 0.6 to 1.2 cm wide and 5 to 15 cm long.
The thin, flat leaves have a prominent midvein running down the centre and a pointed tip but lack ligules or auricles.
Barnyard grass produces green to purple pyramid-shaped seedheads in panicles. The somewhat elliptical and pointed seeds are about 1 to 2 mm long.
It is native to:
- Europe
- India
Removal methods
- Pulling: Hand-pulling or digging can effectively eliminate the weeds.
- Mowing: Mow the lawn frequently at cutting heights below 3 inches to suppress leaf growth.
- Good Lawn Practices: Maintain a healthy lawn or plant turf to outcompete the grass.
- Herbicides: In spring, apply pre-emergent herbicides like prodiamine, pendimethalin, or dithiopyr products. Selective post-emergent herbicides like quinclorac, fenoxaprop-p-ethyl, and topramezone are effective in barnyard grass control. Glyphosate products are recommended for spot treatments only.
4. Horseweed (Conyza canadensis)
- Family: Asteraceae
- Annual or Perennial: Annual
Horseweed is a common weed that can grow up to 3m tall. It produces green leaves about 1 cm wide and 5 to 8 cm long. The leaves on the bottom half of the weed are long, thin, and smooth and cover the central stem.
Typically, the main stem branches out from the plant’s lower half, hosting smaller leaves with toothless margins and tapered tips.
The central stem terminates in a panicle of flower heads. Axillary stems of the upper leaves also produce additional flower heads. The flower heads are cylindrical and produce yellowish-grey fuzzy-like seeds.
It is native to:
- North America
Removal methods
- Pulling: Hand pulling is adequate for younger plants and small infestations. Remove the plants completely as they tend to resprout from broken stems.
- Mechanical methods: Aggressive plow tillage can bury the seeds underground, leading to their death. Horseweed seeds buried below 0.2 inches cannot germinate, leading to death.
- Cover Cropping: Horseweed is sensitive to crop competition, so grow rye or forage radish as a cover crop to suppress the weed’s establishment.
- Mulching: Apply rye or straw mulch to suppress the weed.
5. Johnsongrass (sorghum halepense)
- Family: Poaceae
- Annual or Perennial: Perennial
Johnsongrass is a tall and coarse perennial grass that bolts up to 2m in height. It produces thin, slightly wavy green leaves about 2-7 cm wide and 60 cm long.
The leaves are lanceolate, with a whitish midvein, and primarily occur at the bottom half of the stem.
The weed produces many-branched panicle inflorescence with a pyramid-like outline with individual spikelets about 4-5.5mm long. The seeds are easily recognizable by their oval shape and reddish-brown to black colour.
It is native to:
- Mediterranean Europe
- Asia
- North Africa
Removal methods
- Pulling: Upon discovery, pull out all the grass to destroy seedlings and dig out the roots to prevent establishment.
- Herbicide: Apply glyphosate like Roundup to plants 45 cm tall or early flowering stage to kill the weed.
Lead Editor for Insight Weeds.