Risks of introduction of alien plant species via seeds imported for fodder and birdseed
Agricultural imports, particularly seeds, represent an important route for the introduction of alien plant species. Two studies on the occurrence of alien plants, especially from the genus Ambrosia, in lots of imported seeds have been undertaken. The pollen of Ambrosia artemisiifolia (Asteraceae, EPPO List of IAP) is particularly well known to trigger a severe hay-fever response in some people, thereby constituting a public health hazard.
One study considered the contamination, with seeds of alien plants, of kitchen herbs, seeds processed in livestock feed and vegetable cooking oil. In five products imported from six countries, seeds of at least 67 species were found. Of these, 15 are known as invasive alien plants among which Ambrosia artemisiifolia, Ambrosia trifida (Asteraceae), Bidens pilosa (Asteraceae), Sorghum halepense (Poaceae), and three Ipomoea species (Convolvulaceae).
The second study investigated the occurrence of alien plant species as contaminants of ‘birdseed’ ingredients. The seeds used in such products were from 14 crops and 10 different countries. In addition, 17 lots of mixed feed from Dutch shops were specifically examined for the occurrence of Ambrosia sp. A. artemisiifolia was found in seeds lots of sunflower (Helianthus annuus) and great millet (Sorghum vulgare) imported from France and Hungary. Of these Ambrosia seeds, 36% germinated within 3 weeks. In the mixed feed, A. artemisiifolia was found in two thirds of the lots; of these seeds, an average of 13% germinated in 3 weeks. In the birdseed lots, another 27 non-indigenous and 15 naturalised alien plant species were encountered as well as 21 indigenous species. In these lots, seeds of 17 species considered as invasive were found and included Ambrosia artemisiifolia, Sorghum halepense, Abutilon theophrasti (Malvaceae), Bassia scoparia (Chenopodiaceae), Onopordum acanthium (Asteraceae), Eleusine indica (Poaceae) and, of high interest, Alternanthera philoxeroides (Amaranthaceae, EPPO Alert List). The indigenous species posing the greatest risk of genetic contamination are Chenopodium album (Chenopodiaceae) and Persicaria lapathifola (Polygonaceae).
van Denderen PD, Tamis WLM & van Valkenburg JLCH (2010) [Risks of introduction of alien plant species, particularly from the genus Ambrosia, via seeds imported for fodder and birdseed]. Gorteria 34(4), 67-85 (In Dutch).