Weed Seeds Commonly Found in Specific Vegetable Crops

eOrganic author:

Emily Skelton, Seeds of Change

This is an Organic Seed Resource Guide article.

It is important as a seed grower and seed buyer to understand that weed seeds can be distributed along with crop seed. Noxious weed seed contamination of crop seed is regulated by state and federal regulations. For more information, see the eOrganic article Weed Management in Organic Seed Production. The table below describes weed seeds commonly found as contaminants in vegetable seed lots and the methods used to screen them out.

Table 1. Weed seeds commonly found in specific vegetable crops.
Crop Weed species Listing Difficult to remove due to: Method used Degree of success
Basil Brassica spp (prohibited) 18/lb Same color, size, similar shape Belt grader Fairly successful but a very slow process
Calendula Black bindweed (Polyganum convovulus) 2/lb Same color, size Screens, Indent Cylinder Not very successful
Clover, Yellow Blossom Sweet Brassica spp 18/lb Similar size Screen, indent Cylinder Not very successful
Endive Brassica spp., wild radish, Canada Thistle (Cirsium arvense) 18/lb, 12/lb, prohibited Similar size, color Indent Cylinder Fairly successful
Lettuce (light seeded only) Crabgrass (Digitaria sanguinalis) 27/lb Similar color, shape, size Indent Cylinder Fairly successful
Lettuce Wild lettuce (Lactuca pulchella) prohibited Can't differentiate None Not very successful
Mexican Sunflower Johnsongrass (Sorghum halapense) prohibited Same size, similar shape, color Fanning, screening Not very successful
Onion Black Bindweed (Polygonum convovulus) 2/lb Similar size, color Satake color sorter Color sorter successful, only with green seed coat intact
Peas/Beans Black nightshade (Solanum nigrum), White horsenettle (Solanum elaeagnifolium) berries 9/lb, prohibited Similar size Gravity table Very successful
Dill Black nightshade (Solanum nigrum), White horsenettle (Solanum elaeagnifolium) 9/lb, prohibited Similar shape, color Screen, Indent Cylinder Not very successful
Zinnia Johnsongrass (Sorghum halapense) prohibited Similar shape, size Screens, Indent Cylinder Indent cylinder fairly successful
For more on weed seeds in vegetable seed lots, see Prohibited and Restricted Weed Seed Commonly Found in Vegetable Seed Lots.


This publication contains information about the various state labeling requirements and prohibitions of noxious-weed seeds and shows the botanical names and common names according to the law and regulations of the particular state in which the seed is noxious. It is the responsibility of seed dealers to know the requirements of state laws and the changes in those laws.

Published January 19, 2009

This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.