Weed seed contaminant of bird seed in the USA
Bird seed can be a pathway for invasive alien plant species into new regions. Seeds of invasive plants can be included in bird seed as a contaminant and spread within an area due to humans and birds spreading seed. Although some studies have already been carried out on the possible risks associated with trade of bird seeds (EPPO RS 2007/122), information is generally lacking on the frequency and volume of movement along this pathway. In a study from the USA, conducted between 2016-17, 98 commercially available bird seed mixes were examined for the presence of weed seeds. In 94 seed mixes, Amaranthus (Amaranthaceae) species were present. 74 % of seed mixes had viable Amaranthus seed and 84 % of these Amaranthus contaminated mixes had more than one Amaranthus species present. Amaranthus seeds were germinated, and the developing plants were identified to species level. These species included Amaranthus tuberculatus (present in 23 % of seed mixtures), Amaranthus retroflexus (50 %), Amaranthus palmeri (EPPO Alert List) (28 %), Amaranthus hybridus (4 %), and Amaranthus albus (34 %). Seed of Ambrosia artemisiifolia (Asterales: EPPO List of Invasive Alien plants), Bassia scoparia (Amaranthaceae), Sorghum bicolor (Poaceae), Fallopia convolvulus (Polygonaceae), Chenopodium album (Amaranthaceae), Digitaria sanguinalis (Poaceae), and Setaria species were also present in bird feed mixes.
Note: EPPO has recently carried out Pest Risk Analysis (PRA) on A. tuberculatus and A. palmeri for the EPPO region. Both PRAs are currently under review.
Sources
Oseland E, Bish M, Spinka C, Bradley K (2020) Examination of commercially available bird feed for weed seed contaminants. Invasive Plant Science Management 13, 14-22.