Invasive plants disperse to new areas via numerous pathways. Study of these pathways helps to focus limited budgets toward prevention and early detection. This study examined potentially invasive seed contaminants in imported crops and grass seed as pathways for plant dispersal to Alaska. Crop and grass seed were purchased from 13 Alaska retail outlets representing 14 seed suppliers. Seed bags were sampled using federally mandated protocols and were analyzed for crop seeds that were not supposed to be included and for weed contaminants. Ninety-five weed and 36 contaminant crop taxa were found. Crop seed contained 43 weed taxa and 15 other crop species contaminants, a mean of 6.4 taxa and 3,844 contaminant seed kg−1. Grass seed samples contained 73 weed taxa and 21 crop contaminants, a mean of 3.5 contaminant species and 1,250 seeds kg−1. Two species prohibited by the Alaska seed law were found: Canada thistle was found in a single crop sample, and quackgrass was found in two grass samples. There were no significant relationships between either seed type or supplier and either the number of contaminant species or number of seeds. Labels of 33% of crop samples and 8% of grass samples claimed 0.00% weed seeds, but low (0.007% by weight, 2 species) to high (1.18% by weight, 13 species) amounts of weed contaminants were found. Importation of crop seed is a large pathway for seed movement, causing significant propagule pressure and an increased likelihood of establishment by new invasive plant populations. Prevention of spread via this pathway would be enhanced by changes to seed laws, by greater regulatory enforcement, and by including on the label, the names of all weed and contaminant crop species found in the law-required samples. Consumers could then make decisions on whether to purchase seed based on the potentially invasive species that would be planted with the desired seed.
Nomenclature: Canada thistle, Cirsium arvense (L.) Scop.; quackgrass, Elymus repens (L.) Gould.
Management Implications: Seeds of invasive and other nonnative plants disperse to new areas via numerous pathways. Study of these pathways helps to focus limited budgets on prevention and early detection. This study examined the pathway of seed contaminants traveling to Alaska via imported crop and grass seed. Crop and grass seed were purchased from 13 retail seed outlets in Alaska and included 14 seed suppliers. Eighteen crop samples and 100 grass seed samples were collected and sampled using federally mandated protocols. Seed samples were analyzed for crop and weed contaminants using an approved laboratory. A total of 95 weed and 36 contaminant crop taxa were found. The average number of contaminant taxa was 6.4 for crop seed and 3.5 for grass seed. The average number of contaminant seed per kilogram of seed was 3,844 for crop seed and 1,250 for grass seed. Two species prohibited from transport or sale in Alaska were found in the samples: Canada thistle was found in a single crop sample, whereas quackgrass was found in two grass samples. Seed labels of 33% of crop seed samples and 8% of grass seed samples claimed to have 0.00% weed seeds yet contained numerous weed species. Six percent of crop samples and 8% of grass samples did not contain crop or weed contaminants, showing that it is possible to produce clean seed. Statistical analysis showed no differences between seed suppliers or crop species in the number of contaminant taxa or amounts of contaminant seed. Importation of seed into Alaska is a large pathway for movement of nonnative plants. Contaminant seed using this pathway are likely to establish because they are planted under enhanced conditions for survival with the crop seed. Prevention of spread via this pathway would be aided by revising seed laws, increasing regulatory enfor