Pompom Weed (Eupatorium macrocephalum)

Pompom weed (Eupatorium macrocephalum) is a perennial flowering plant that grows to 1.3m tall. It has a rhizomatous root system and stems covered by rough, bristle hairs. 

You can easily identify the plant by its showy pink flowers, covered by purple bracts. 

Eupatorium macrocephalum Scientific Classification

  • Domain: Eukaryota
  • Kingdom: Plantae
  • Phylum: Tracheophyta
  • Subphylum: Spermatophytina 
  • Class: Magnoliopsida
  • Order:  Asterales
  • Family: Asteraceae 
  • Genus: Eupatorium 
  • Species: Eupatorium macrocephalum
  • Common Names: Pompom weed or pompom bossie

Nativity & Distribution

Pompom weed is native to: 

  • South America (Brazil, Bolivia, Colombia, Paraguay, and Argentina)
  • Central America (Guatemala and Honduras)
  • Southern United States
  • Mexico

Physical Characteristics

Pompom has purplish-green stems and showy pink flowerheads
Pompom has purplish-green stems and showy pink flowerheads. Image:invasives.org.za
  • Leaves: Light-green lanceolate to elliptical leaves with serrated margins.  
  • Fruits: Brown, single-seeded achenes with simple bristles.  
  • Stems: Erect purplish-green stems that are covered with hairs. 
  • Flowers:  Pink to light purple flowerheads blooming at the stems’ tip.  
  • Roots: Short, woody, tuber-like rhizomatous, perennial roots. 

Eupatorium macrocephalum is a rhizomatous perennial flowering plant native to the Americas. It is usually found in disturbed sites, such as roadsides, but it can quickly invade grasslands, wetlands, and other landscape areas. 

It is quickly identified by its showy pink to purple fluffy flowerheads, which resemble pompoms, hence the name “pompom weed.” 

The plant has erect, green stems with purple tinges covered in rough, bristle hairs. The stems die back to the root crown annually before new ones sprout from the root rhizomes. 

Its leaves are light green, covered in bristle hairs, lanceolate to elliptical, and 8cm long by 2cm wide. The margins are serrated, with the teeth larger at the base of the leaf blade before becoming smaller away from the petiole. 

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Pompom weed leaves form a dense rosette at the ground level. On the other hand, upper leaves are scattered along the stem and are usually smaller than the basal ones. 

Its pink, fluffy flowers bloom in clusters at the tip of the stems. Each flower head has several small, star-shaped florets surrounded by purple bracts. 

The flowers bloom from late summer (December to March) before developing into blackish-brown, one-seeded achenes. The mature achenes are about 5mm long and have a pappus of simple bristles. 

Reproduction, Dispersal, & Life Cycle

  • Life Cycle: Perennial (however, the stems die down to the roots annually). 
  • Seeds: A single plant can produce over 2,000 seeds.
  • Climate: It does well in temperate climates with full sun or partial shade.  
  • Dispersal: Wind

Eupatorium macrocephalum is a prolific seeder; a single plant can produce over 2,000 seeds per season. The seeds have a relatively high germination rate of over 25% and can sprout on the soil surface or in shallow soil. 

Seeds can remain dormant but viable for up to five years, surviving even temperature and rainfall fluctuations. 

The seeds are mostly dispersed by wind. However, they can also be carried by people through vehicles (after they stick on muddy wheels) or when individuals pick and discard the flower heads. 

Besides sexual production through seeds, pompom weed reproduces vegetatively through its underground rhizomes. 

Uses

  1. It is considered a medicinal plant in Paraguay and is used as a sedative and anti-inflammatory. 
  2. It is cultivated as an ornamental plant due to its showy, attractive flowerheads. 
  3. It can be used as fodder for goats. 
  4. The extensive rhizomatous root system makes it a good choice for preventing soil erosion. 
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Impact on Farms and Environment

The aggressive weed invades grasslands, wetlands, and open savannah areas
The aggressive weed invades grasslands, wetlands, and open savannah areas. Image: Flickr/gerdavanschalkwyk

Pompom weed is listed as an invasive species in South Africa. It is also classified as a weed in Brazil. 

In South Africa, it is considered a serious threat to the conservation of grassland areas. It is aggressive and invades grasslands, wetlands, and open savannah areas, displacing the native vegetation and greatly affecting the biological diversity of these areas. 

E. macrocephalum can also invade grazing areas, reducing the grazing capacity of native plants. 

In addition to being highly invasive, the plant is very hardy and difficult to eradicate. It spreads aggressively through its seeds and rhizomatous root system. 

The underground roots are also perennial and sprout new shoots after the stem dies. In addition, the roots help to protect the plant and ensure its longevity in case of fires, frost, or other harsh conditions. 

Control

  • Mechanical control: Hand-pulling (for young plants) and repeated cutting to the root crown before seeding. 
  • Natural methods: Prescribed burning. 
  • Chemical control: Picloram and Metsulfuron methyl (when growing in grasslands) and glyphosate (when growing in areas roadsides and non-crop areas). 

Eupatorium macrocephalum invades disturbed sites that have unhealthy crops or are bare. 

Therefore, one of the best ways to prevent infestation is to keep the natural vegetation or beneficial crops healthy and vigorous. You can also plant competitive groundcover crops in areas vulnerable to invasion. 

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When prevention is no longer an option, you can find several control solutions to eradicate the plant. For small patches of young seedlings, you can hand-pull or dig out the plant from the ground, making sure you remove the entire root system. 

Hand-pulling and digging are, however, time-consuming when dealing with a large infestation. These techniques can also disturb the soil, leading to the germination of dormant seeds.

Likewise, tilling the land is not advisable as it can disturb the soil or cut up and spread the root rhizomes, leading to new germinations. Therefore, the only other solution is to repeatedly cut the stems to the root crown, which can overwhelm the plant and, eventually, kill it. 

E. macrocephalum can also be controlled by burning, which destroys the stems, forage, and seeds in the soil. However, this can stimulate the underground roots to produce new shoots, so you must burn new germinations or combine fire with another control measure. 

Lastly, herbicides can eradicate pompom weeds. Selective herbicides like picloram and metsulfuron-methyl can be used for grasslands or areas with crops. 

You can also apply non-selective herbicides like glyphosate (Roundup) if the weeds are growing in road sides or other areas where you can’t harm beneficial crops or native vegetation. 

You can combine two or more control measures for better results. For example, you can apply herbicides to new seedlings that sprout after burning or cutting down the stems.