Common groundsel (Senecio vulgaris) is a prevalent annual weed found in gardens, agricultural fields, and disturbed areas. It establishes quickly, making it a common presence in many landscapes.
Identifying Groundsel
Groundsel has distinct physical characteristics. Its leaves are deeply lobed with coarsely toothed margins and are alternately arranged on the stem. Young plants often form a rosette at the base. Leaves can be hairless or lightly covered with wavy or cotton-like hairs, and basal leaves may have a purplish tint underneath.
The stems are erect, hollow, and branched, typically growing 6 to 18 inches (15-45 cm) tall, sometimes reaching 2 feet (60 cm). They can appear purplish, especially at the base. Groundsel produces small, yellow, cylindrical flower heads in clusters at the stem tips. These flowers lack showy ray florets, giving them a thimble-like appearance, and are surrounded by green bracts often tipped with black.
After flowering, the heads develop into fluffy white seed parachutes, similar to dandelions, known as pappus. These aid in wind dispersal of its slender, ridged seeds. As an annual plant, groundsel completes its life cycle from seed to seed in as little as five to six weeks, allowing multiple generations per year, especially in mild climates. It thrives in disturbed soils, cultivated areas, open fields, and roadsides, preferring nutrient-rich, exposed ground.
Why Groundsel is Problematic
Groundsel is problematic due to its toxicity, competitive nature, and rapid reproductive cycle. The plant contains pyrrolizidine alkaloids (PAs), which are toxic to livestock like horses, cattle, and sheep. These compounds cause chronic, irreversible liver damage, potentially leading to serious health issues or even death in affected animals. PAs can also pose risks to humans through contaminated food or herbal remedies, with potential for liver damage, birth defects, and cancer.
This weed competes aggressively with desired garden plants and crops for water, nutrients, and sunlight. It rapidly absorbs these resources, hindering the growth and yield of cultivated plants. Its quick growth cycle and robust root system allow it to outcompete slower-growing seedlings in gardens and agricultural settings.
Groundsel is a prolific seed producer, with a single plant capable of generating thousands to a million wind-dispersed seeds. The seeds are equipped with a feathery pappus, enabling them to travel far by wind. This rapid seed production and effective dispersal contribute to its quick re-establishment and spread, leading to continuous weed pressure.
Controlling Groundsel
Controlling groundsel involves a combination of strategies to manage its presence. The most successful approach integrates manual removal, cultural practices, and, when necessary, chemical controls.
Manual Removal
Hand-weeding is effective for controlling groundsel, especially when plants are young and before they produce seeds. Remove the entire root system to prevent regrowth, aided by a trowel or weeding fork to loosen soil. Prompt disposal is advisable, as groundsel can mature seeds even after uprooting, especially if flowering. Consistent removal throughout the growing season is necessary to manage new growth, as groundsel produces multiple generations annually.
Cultural Practices
Mulching is valuable for suppressing groundsel. Applying a thick layer of organic mulch, such as wood chips or straw, can reduce germination by blocking sunlight. A layer of 2-4 inches (5-10 cm) is effective. Coarse mulches are preferred as they allow water to pass while preventing weed establishment.
Proper planting and spacing also help. Densely planting cultivated vegetation creates a canopy that shades the soil, reducing light for weed seeds. Healthy, robust plants naturally outcompete weeds for water, nutrients, and sunlight, making the garden less hospitable. Improving soil health through regular addition of compost and organic matter supports vigorous growth of cultivated plants, enhancing their competitiveness.
Chemical Control
Chemical control offers another option for groundsel management, with both pre-emergent and post-emergent herbicides available. Pre-emergent herbicides prevent weed seeds from germinating by forming a chemical barrier in the soil. Products with active ingredients like pendimethalin or isoxaben can be applied before groundsel seeds sprout, typically in early spring or fall, to prevent new growth. Timing is crucial, as they must be applied before germination.
For existing groundsel plants, post-emergent herbicides are used. Non-selective options, such as glyphosate, kill most plants they contact and require caution around desirable vegetation. Selective broadleaf herbicides target weeds like groundsel without harming most turfgrasses, and are available for lawns. Always read and follow product label instructions, including wearing protective equipment and understanding application rates. Considering environmental impact, integrating these methods with manual and cultural practices provides the most effective and sustainable long-term groundsel management.