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Non-native seeds detected by freight containers pose significant threats

Nonnative plant seeds refrigerated shipping containers

With vacuum cleaners in their backpacks, the research team searched for non-plant seeds on air intake grilles in refrigerated shipping containers – and found thousands of them. Credit: Rima Lucardi, USFS

Seeds floating in the air can go for walks in unusual places – like the air intake grille in a refrigerated container. A team of researchers from the USDA Forest Service, Arkansas State University and other organizations recently conducted a study that involved vacuuming seeds from air intake grilles over two seasons in the Port of Savannah, Georgia.

The viability of such seeds is of significant interest to federal regulatory and enforcement agencies, and the project required a shared management approach. Imported refrigerated shipping containers are inspected by the US Customs & Border Protection, Agriculture Program (Department of Homeland Security). The research team worked closely with this agency as well as the USDA Animal and Plant Health Inspection Service and the Georgia Ports Authority.

Their findings were recently published in the journal Scientific reports. Seeds from 30 plant taxa were collected from the grids for air intake, including seeds of wild sugarcane (Saccharum spontaneum), a grass on the USDA Federal Noxious Weed List.

Federally harmful weeds pose immediate, significant threats to agriculture, nursery and forestry. Although it is a lovely grass and useful in its original range, wild sugar cane has the potential to join cogon grass, stilt grass and other non-native species that have become extremely widespread in the United States.

“During the two ship seasons, we estimate that over 40,000 seeds of this species entered the Garden City Terminal at the Port of Savannah,” said Rima Lucardi, a researcher at Forest Service and lead author of the project. “This amount of incoming seed is more than sufficient to cause the introduction and establishment of this non-inward intruder, even if the escape rate from the shipping containers is limited.”

To estimate the chance that seeds would survive and establish themselves in the United States, Lucardi and her colleagues analyzed and modeled viable seeds from four plant taxa. All are lush seed producers, wind-pollinated and windswept and able to continue under a wide range of environmental conditions and climates.

The researchers propose several possible strategies for reducing the risk to native ecosystems and agricultural commodities. For example, instead of laborious vacuuming of air intake grilles, a liquid pre-emergent herbicide could potentially be applied to containers while in port. Prevention and best management practices from farm to store reduce the likelihood of non-seeds being established in the United States. Inspection of external seeds that run on shipping containers at their places of origin or stops along the way will also reduce the risk of invasion.

Preventing non-plant invasions in the long run is far more cost-effective than trying to control them once they have spread and become widely established. “Investing in the prevention and early detection of non-stemmed plant species with known adverse effects results in almost a 100-fold increase in economic returns compared to managing widespread non-natural species that can no longer be contained,” says Lucardi.

The team had previously shown, in PLOS One, that the port is a hotspot of non-vegetative plant diversity and wealth.

Reference: “Seeds attached to refrigerated shipping containers represent a significant risk for the introduction and establishment of non-vegetative plant species” by Rima D. Lucardi, Emily S. Bellis, Chelsea E. Cunard, Jarron K. Gravesande, Steven C. Hughes, Lauren E Whitehurst, Samantha J. Worthy, Kevin S. Burgess and Travis D. Marsico, September 14, 2020, Scientific reports.
DOI: 10.1038 / s41598-020-71954-3

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