birdseed, chickenweed, grinsel, grundsel
Senecio vulgaris L.
Groundsel is a native annual, ephemeral or overwintering weed present on almost all soils and is especially prolific on good land. It is common throughout the UK in open and rough ground in a range of habitats. Groundsel is abundant on horticultural land and rubbish heaps. It may occur in vast numbers that can smother a young crop. It is a weed of arable and horticultural crops and is a common garden weed.
Plants have a very variable habit and leaf shape. The level of variability depends on the amount of soil disturbance. In a frequently disturbed soil more genotypes are recorded, in a less disturbed habitat the population is more stable. Some plants have ligulate ray florets and hybrids occur with Oxford ragwort, S. squalidus. It is essentially and inbreeding species and ecotypes have developed with tolerance to saline conditions and to acid rain. Races of groundsel have developed with resistance to one or more herbicide groups.
Groundsel acts as a host for Cinerarea leaf rust and the fungus that causes black root rot in peas. It can also carry seed transmitted virus diseases that attack important crop species. The plant has diuretic properties and has been used medicinally in the past. Consumption of large quantities of groundsel by stock animals can cause liver damage. The alkaloids responsible are not destroyed by drying or by fermentation in silage.
Groundsel flowers and sets seed throughout the year. An individual plant may continue to flower and set seed for several months. The main period of flowering is April to October and most seed is set from May to October. The flowers are usually self-fertilised. Flower stems cut in bud do not ripen viable seed but seed from plants cut in flower had germination levels of 35%. Groundsel produces around 1,200 seeds per plant.
Most seeds can germinate at once and seedlings emerge within a few days of seed shedding. Freshly shed seed of groundsel generally requires light but not stratification for germination. However, it has been noted that seed produced in spring is somewhat more dormant than seed produced in summer or autumn. Seed germinates better at lower (10-15 °C) rather than higher (20-30 °C) temperatures. Seeds buried for 6 months in soil under natural conditions germinate readily on exposure to light. Seed germination is increased by a period of dry storage.
Seedling emergence generally occurs from February to December with the main peak from June to October or in May and September. Flushes of emergence are probably related to rainfall events that follow soil cultivation or seed shedding. Germination and establishment is better in conditions of high humidity. In sand, sandy loam and peat soils, field seedlings emerged from the top 30-40 mm of soil with up to 80% emerging from the surface 5 mm.
Seedlings are frost tolerant but little germination occurs in winter until the temperature begins to rise. Groundsel can complete its life cycle in 5-6 weeks. The cycle may take longer in richer soils. At high levels of soil moisture and elevated carbon dioxide levels, the horizontal spread and branching of groundsel roots increases. The greater overall length of the roots allows them to forage through the soil in drought conditions.
In studies in cultivated soil, 85% of seeds had germinated within 1 year and 100% within 5 years. In undisturbed soil, groundsel seed had declined by 87% after 6 years. Losses were due to germination and to seed death in equal amounts. Seed buried deeper in soil persists longer than seed in the upper layers of soil.
The seeds have a pappus of hairs and are widely dispersed by the wind. Laboratory tests suggest maximum seed dispersal distances of 1.9 and 2.9 metres at wind speeds of 10.9 and 16.4 km/hour respectively but this would be affected by plant height. The pappus also aids dispersal by adhering to clothes and to animal fur.
Groundsel seed has been found in the droppings of sparrows, and seedlings have been raised from the excreta of various birds. Seed has also been found in cow manure. Groundsel seed was a contaminant of cereal and vegetable seeds, but not of grass and clover seed in the UK.
Groundsel may be controlled by cultivation with the hand or tractor-hoe. Stubble cleaning is effective in dealing with shed groundsel seeds. The surface soil should be cultivated to a depth of 50 mm and the operation repeated at 14-day intervals. The area around manure heaps, where the weed often occurs in abundance, should be kept clean to prevent groundsel seed contaminating the manure.
Seed numbers in soil may be reduced by around 70% after fallowing for 1 year. Seed numbers are reduced to a lesser extent under cropping with winter wheat. Crop competition reduces seed production by shading out the weed. Regular fallowing every 5th year over a 15-year period stabilised seed numbers at a low level provided that the groundsel was not allowed to grow uncontrolled during the intervening cropped years.
Groundsel seed numbers increased in soil during a 2-year set-aside left fallow but not when there was a sown grass cover. The weed cannot exploit grazed, trampled or mown sites.
Groundsel seedlings with 2-6 leaves are tolerant of flame weeding but the seeds are susceptible to soil solarization. The seeds are also killed by soil steaming treatments.
Biological control control of groundsel with the naturalised rust fungus Puccinia lagenophorae Cooke has been the subject of much research. The fungus now occurs widely in the UK and may cause considerable damage to groundsel plants but there is no guarantee of an attack by the pathogen. Also different lines of the weed vary in susceptibility to the fungus. Caterpillars of the cinnabar moth Tyria jacobaeae feed on groundsel in June-July and may weaken or even kill a plant before it can set seed. The caterpillars themselves are attacked by several different predator insects that can have a drastic effect on their numbers and hence effectiveness.
Updated October 2007.