Khaki weed (Alternanthera pungens), sometimes called Khaki Burr or Creeping Chaffweed, is a highly invasive plant that aggressively colonizes disturbed areas. This South American native forms dense, low-growing mats that quickly outcompete desirable grasses and groundcovers. Its robust, deep taproot and efficient seed dispersal make eradication challenging. Successful control requires a comprehensive strategy that attacks both the established perennial rootstock and the prolific annual seeds.
Identifying Khaki Weed and Understanding Its Growth
Khaki Weed is characterized by its prostrate growth habit, forming a dense, carpet-like mat close to the soil surface. The stems are reddish, trail up to 60 centimeters long, and are covered in fine, silky hairs. Its oval leaves are arranged in opposite pairs, with one leaf often noticeably larger than the other.
As a perennial, the above-ground foliage dies off in cooler months, but a large, woody taproot remains dormant underground. This deep taproot allows the weed to survive drought and makes manual removal difficult. New growth emerges from this root crown each spring.
The primary mechanism for spread is the Khaki Burr, a prickly, khaki-colored fruit that develops from inconspicuous white flowers. These spiny burrs easily detach and cling to shoes, clothing, vehicle tires, and animal fur, dispersing seeds over wide areas. Seeds remain viable in the soil for several years, ensuring the weed’s continued presence.
Manual and Cultural Methods for Eradication
Manual removal is effective for small infestations, provided the entire perennial taproot is extracted. Digging at least 100 millimeters deep ensures the fleshy taproot and crown are completely removed. If any part of the taproot is fragmented and left in the soil, the plant can readily regrow.
Timing is an important factor, with removal being most effective before the plant flowers and sets its prickly burrs. Any pulled material containing burrs must be disposed of carefully to prevent further seed dispersal. The pulled weeds should be bagged and sent to a landfill or incinerated, never placed in a compost pile or green waste bin.
Cultural controls focus on improving turf density to outcompete the weed, which thrives in thin, disturbed areas. Mowing the lawn at a higher blade setting encourages a healthier, denser turf canopy that shades the soil, restricting the Khaki Weed’s ability to spread and establish. Regular watering and proper fertilization also promote turf vigor, helping the grass naturally crowd out the weed.
In non-turf areas, smothering techniques like soil solarization are highly effective. This involves covering the area with clear plastic sheeting during the hottest months of summer for four to eight weeks. The plastic traps solar heat, raising the soil temperature high enough to kill established plants and the seed bank in the top six inches of soil. Before sealing the plastic down, the area must be cleared of debris, raked smooth, and thoroughly watered.
Effective Chemical Control Strategies
Chemical control is often necessary for large or persistent infestations, utilizing a combination of pre-emergent and post-emergent herbicides. Pre-emergent herbicides target seeds before they germinate and should be applied when soil temperatures are between 16 and 21 degrees Celsius. Active ingredients such as Isoxaben, Pendimethalin, or Prodiamine prevent new seedlings from establishing. Isoxaben, in particular, requires activation with a half-inch of water.
Post-emergent herbicides are designed to kill established plants. Khaki Weed is a broadleaf weed, and combination products containing synthetic auxins like 2,4-D, Dicamba, and MCPP (or Mecoprop) are recommended for selective control in turfgrass. These hormonal herbicides are absorbed through the leaves and translocate throughout the plant, interfering with its growth processes.
Application should occur when the weed is small and actively growing, typically in the spring or early summer, and before the prickly burrs form. Due to the thick, waxy cuticle on the Khaki Weed leaves, adding a non-ionic surfactant to the herbicide mixture is important to ensure the chemical penetrates the leaf surface. Repeat applications, often four weeks apart, are required to achieve consistent, season-long control of the perennial rootstock and any new growth.
For spot treatment in non-lawn areas like driveways or garden beds, a non-selective herbicide like Glyphosate can be used, but it will kill all vegetation it contacts. When using any chemical method, safety protocols must be followed rigorously, including wearing appropriate personal protective equipment. Avoid application during windy conditions to prevent drift onto desirable plants. Always consult the product label for specific mixing ratios and application instructions.