BANFF, Alta. – Thousands of plant species are used in Asian medicines and spices but can become problem weeds when imported into North America.
Indira Singh, an official with the U.S. Department of Agriculture’s animal and plant health inspection service, told a North American weed conference in Banff May 30 that these weeds may slip into the country unnoticed because inspectors cannot examine every container and they may not know how to identify them.
“These are difficult to identify because the medicines are highly processed and in many cases they bear no resemblance to the original plant,” Singh said.
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As well, many labels bear the Chinese or pharmaceutical name rather than the scientific label.
Shipments that are identified by port inspectors and deemed harmful could be ordered changed, destroyed or returned.
Border inspections may be painstaking, but Singh said the U.S. government believes it is cheaper to intercept these weeds at the border rather than pay to control them once they become established.
Prohibited weeds are rarely brought to North America deliberately, but she said it is difficult to educate importers about them.
Foreign weeds may be found in seeds used in Asian herbal medicine, Mediterranean spices, dried plant arrangements and plants imported for aquariums that may later be dumped in ponds and rivers.
Pests can also be imported through purchases made on the internet or hitchhike in with other commodities. For example, weed seeds could be found in imports of fennel or fenugreek.
Spores have been found in the crowns of pineapple from Costa Rica that resulted in the fruit being returned. 
“It is a perfect hiding place, not only for weed seeds but for a lot of pests, and very large numbers of shipments have been refused since November 2005,” Singh said.
Some ethnic groups use noxious weeds as food. They import the seeds, plant them and sell them in fresh vegetable markets.
“This is how they are frequently intercepted when our people do fresh market surveys.”
The USDA requires seeds to be certified as unviable, but the department still runs germination tests as a further guarantee. The law says imported seeds must be heat treated or ground, but Singh said 15 percent are not. These could germinate and cause problems, she added.
