Ambrosia artemisiifolia

Common ragweed) is an invasive weed in Europe, native from North America. Its presence is increasing in all the European countries, in both agricultural and non-agricultural areas (in particular along roadsides and in river banks). It is considered an important, noxious weed because of its allergenic properties and its competitiveness with crops. Pollen of flowering plants may cause allergenic reactions (rhinitis) to humans. Common ragweed has become a dominant weed in many arable and vegetable crops, especially in spring sown crops such as maize and sunflowers for which there are currently very few effective control methods. In this regard, an important role has been played by the continuous monocropping, or short rotations, and by the frequent application of weed control strategies (mainly herbicides). Management of A. artemisiifolia in EMPHASIS will focus on efficient control of this weed in summer crops (maize, sunflower) by selective herbicides to reduce its competitive effect and resulting yield losses. In addition mechanical removal during intercropping (in particular on cereal stubble) will favour depletion of seeds in the soil. In non-cultivated areas a combination of chemical (non-persistent broad-spectrum herbicides) and mechanical intervention will be assessed within WP3 and validated within WP4.2.

Species Description

Habitus: herbaceous, annual, aromatic, 20-100 cm high.
Stem: upright and very branched; hairless or pubescent, reddish green.
Roots: taproot.
Leaves: green on both pages, petiolate, deeply incised lamina with lateral laciniae often incised or toothed, pubescent lamina on the upper page.
Flowers: small, unisexual, green, inconspicuous. Male flower heads in terminal racemes are numerous, pendulous, small (0.3-0.5cm diameter). Female flower heads, in the axils of the upper leaves, are few and sessile.
Fruits: fusiform obovoid achenes (containing only one seed each), 0.2-0.3cm long, with 4-5 erect spiny teeth.

Biology and Ecology

Ecological requirements: thermophilus and heliophilous pioneer species, commonly present in areas disturbed by human activities like soil movement and agricultural practices, or in riparian areas by flooding activity. Prefers sandy soils, rich in nutrients, with neutral to acid pH. Tolerates aridity, high summer temperatures and a moderate salinity of the soil. Fertilizations with N, P, Ca and K increase fruit production.
Pollination: anemophilous, male flowers begin to produce pollen in August and constantly increase up to be maximum in September. Pollen can be transported more than 40km away from the plant that produced it. Seed production and dispersal: produce a large amount of seeds, more than 3000 each plant, which accumulate in the soil forming a considerably seed bank. Seeds maintain their viability for at least 20 years. Seed dormancy can be broken by following a period of low temperatures and rains. Natural seed dispersion is mainly barochory, but also zoochory (birds) or hydrochory. However, involuntary transport due to anthropogenic activities is one of the main causes of diffusion, especially over long distances.
Propagation: high resprouting ability and flowering after cutting, even with small plants.
Flowering: between July and October (Northern Italy).
Environment: commonly present in disturbed ruderal areas such as roads, railways, gravel pits, urban construction sites, gardens, uncultivated areas, field margins and sandy river banks. It is considered a weed of many crops like sunflower, sugar beet, wheat and other cereals.

Impacts

Ecosystems: A. altissima is a short-lived species (30-50 years) but its ability to sprout constituting pure areas of infestation, that hampers the growth of other species, permits to dominate the infested sites indefinitely. The reduction of biodiversity caused by this species is also due to its allelopathic potential: bark and leaves can release allelopathic compounds that inhibit or affect the germination and the growth of other plants.
Agriculture: leaves are toxic for animals, but because of the bitter taste are relatively unpalatable compared to other species.
Human health: bark, leaf and root saps can cause skin irritation to some people due to the alkaloid ailanthin. Pollen may cause allergy reactions.
Buildings: the fast-growing root system can damage buildings, foundations, sidewalk, roads, archaeological sites and also roofs and cracked walls of unmanaged buildings.

Management approach

For Optimized chemical control: Selective means of control on summer crops and broad-spectrum herbicides on cereal stubble
For Cultural control: Mechanical interventions (cutting, girdling)/ reduction of seed production

Solution proposed by EMPHASIS

For Optimized chemical control: Guidelines for sustainable IPM control of weeds in agricultural and non-agricultural areas (PU) into IPM protocoles
For Cultural control: IPM protocols

Contact person/organisation

Aldo Ferrero (UNITO)