Spikeweed (Centromadia pungens) is an annual plant found in various environments, especially disturbed areas. It is recognized by its rigid, branching structure and distinctive spiny features. Common names include tarweed or maritime spikeweed.
Identifying Spikeweed
Spikeweed grows from 4 inches to 4 feet tall. Its rigid stems branch freely. The plant’s leaves and the bracts at the base of its flower heads are spine-tipped.
Lower leaves are typically divided into narrow, linear lobes, while upper leaves are linear and also spine-tipped. The plant produces numerous small, yellow flower heads that bloom from July to September. The bracts surrounding these flower heads are spine-tipped.
Where Spikeweed Thrives
Spikeweed thrives in disturbed and open environments. It is commonly found along roadsides, in waste areas, cultivated fields, open alkaline flats, depressions, seasonal wetlands, grasslands, and saltbush scrub. Originally native to central California’s dry grasslands, spikeweed has become an invasive weed in northeastern Oregon and southeastern Washington, especially in the Columbia River basin.
Why Spikeweed is a Problem
Spikeweed is a nuisance in natural and agricultural settings. It competes with desirable plants and crops for moisture and nutrients, reducing yields and overall plant health. Its dense, spiny stands can impede livestock and wildlife movement. Prolific seed production allows it to spread rapidly, creating persistent infestations.
Controlling Spikeweed
Controlling spikeweed involves various methods, depending on the infestation’s scale and environmental considerations. For small populations, manual removal is effective. Hand-pulling is best done in spring when plants are soft, but wear gloves due to their spiny nature. Removing the entire root system is important to prevent resprouting, especially in loose or damp soils.
Cultural practices also suppress spikeweed growth by promoting desired plants. This includes ensuring optimal growing conditions for beneficial plants, such as proper spacing and fertilization. Mulching suppresses weed growth by shading the soil and preventing seed germination. Crop rotation can disrupt the weed’s life cycle.
For larger infestations, chemical control methods like herbicides are used. Pre-emergent herbicides create a barrier to inhibit seed germination and are applied before seeds sprout, typically in late winter or early spring when soil temperatures reach 50-55°F. Post-emergent herbicides are applied after weeds emerge and are most effective on young, actively growing plants. Proper timing is crucial, as environmental factors like temperature, humidity, and rainfall affect performance. Always follow product label instructions for safe and effective application.
Preventing Spikeweed
Preventing spikeweed establishment requires a proactive approach. Maintaining healthy plant beds with dense, desirable vegetation suppresses weed growth. Improving soil health, including balanced nutrient levels and good structure, makes the environment less conducive to weed growth and proliferation. Minimizing soil disturbance can reduce the emergence of dormant weed seeds from deeper soil layers.
Utilizing pre-emergent treatments in late winter or early spring significantly reduces spikeweed seedlings. These treatments form a chemical barrier, preventing weed seeds from developing. Consistent and vigilant monitoring for new spikeweed plants allows for early intervention, as removing isolated plants before they establish and produce seeds is more effective than managing widespread infestations.