Officials in at least 28 states are urging residents to report any unsolicited packages of seeds that appear to have been sent from China because they could be harmful.
The agricultural departments in those states released statements in recent days saying residents had reported receiving packages of seeds in the mail that they had not ordered.
"Based on information provided by constituents, the packages were sent by mail and may have Chinese writing on them," the Delaware Department of Agriculture said in a statement Monday. "All contained some sort of seed packet either alone, with jewelry, or another inexpensive item."
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Public notices about unsolicited shipments of seeds from China were also issued by agriculture officials in Alabama, Colorado,Florida, Georgia, Iowa, Kansas, Kentucky, Louisiana, Maryland, Minnesota, Mississippi, Montana, Nebraska, Nevada, New Hampshire, New Jersey, North Carolina, North Dakota, Oklahoma, South Carolina, Tennessee, Texas, Virginia, Washington state, West Virginia and Wyoming.
Some of the seeds have been mailed in white packages displaying Chinese lettering and the words "China Post." Others, such as those mailed to people in Ohio, have been sent in yellow envelopes.
The U.S. Agriculture Department's Animal and Plant Health Inspection Service is working with U.S. Customs and Border Protection and state departments of agriculture to investigate.
The USDA said in a statement it did not have any evidence that this was something other than a "brushing scam," where people receive unsolicited items from a seller who then posts false customer reviews to boost sales.
"USDA is currently collecting seed packages from recipients and will test their contents and determine if they contain anything that could be of concern to U.S. agriculture or the environment," the statement said.
The USDA urged anyone who received the seeds in the mail to contact state plant regulatory officials or Animal and Plant Health Inspection Service officials in their state.
Officials warned people not to plant the seeds.
"If you receive seeds from China, DO NOT PLANT THEM. And don’t throw them in the trash," Mississippi Agriculture and Commerce Commissioner Andy Gipson said in a statement on his Facebook page.
The Montana Department of Agriculture said in a statement Monday that the seeds have not yet been identified.
"They could be invasive, meaning they may have the potential to introduce diseases to local plants, or could be harmful to livestock," the statement said.
Steve Cole, director of Clemson University's Regulatory Services unit in South Carolina, said: "If these seeds should bear invasive species, they may be a threat to our environment and agriculture. We don't want unknown species planted or thrown out where they may wind up sprouting in a landfill."