Tuesday, June 19, 2012

Close-up view of the parasitic dodder (Cuscuta) vine-bearing an insect induced gall.

Chinese Soybeans, Weed Seeds, and Probability

         I have a two-part story to share. The first part began here in Oregon about two weeks ago. The second part takes place in the future—I created it to illustrate a point. The story starts with the arrival of a shipment of organic soybeans from China at the Port of Portland. The soybeans were destined for a processing plant in Rickreall where they would have been turned into organic chicken feed. They didn’t get there.

         Customs and Border Protection (CBP) inspectors took samples at the dock and found two species of noxious weed seeds contaminating the soybeans—dodder (Cuscuta sp.) and Benghal dayflower (Commelina benghalensis)—both are on the federal noxious weed list. CBP issued an emergency action notice stopping the soybeans from entering the country.

         The importers had a lot of money tied up in the shipment and customers waiting; they pleaded for leniency or some special process to allow the soybeans to enter the United States. Officials at the US Department of Agriculture (USDA) and Oregon Department of Agriculture (ODA) discussed options for a rescue treatment and other forms of mitigation. Fumigation is sometimes an option in situations like this, but not with weed seeds—seeds are not on the available herbicide labels, and there is no data indicating they would effectively kill the seed without greatly reducing the organic nature of the soybeans.

         Sealing the containers and allowing them to proceed to destination was considered. Making chicken feed out of soybeans involves several steps including grinding and exposure to high heat. The processed chicken feed itself would probably be low risk, so why not seal the containers and let the soybeans proceed to the manufacturing plant? An inspector could be present to make sure everything was processed accordingly. The importer was willing to pay for the inspector’s time. Would you have allowed that?

         ODA said “No.” Our reason for not allowing the contaminated soybeans into Oregon is illustrated by the following fictional account of what could have happened. Numbers have been rounded for ease of calculation.

         Assume 20 containers each with 50,000 lbs of soybeans for a total of 1 million lbs. CBP took several samples of about two gallons each and found 10 dodder and 10 Benghal dayflower seeds per sample. Let’s estimate that two gallons of soybeans weighs 10 lbs so that we’re dealing with 2 weed seeds per lb, one of each species.

         Dodder seeds are hard and small, somewhere between a speck of dust and a grain of sand in size. Benghal dayflower seeds are also hard, but larger, about the size of a grain of rice. Thus our fictional account begins with 2 million weed seeds mixed in to 500 tons of soybeans on the dock in Portland. In this scenario, ODA says “Yes” to allowing the shipment to enter the state and proceed to Rickreall. Being cautious, they require the containers be sealed first so that the chance of weed seeds dribbling out along the highway is minimized. The system works and all the soybeans and the weed seeds arrive at their destination.

         Next the containers are dumped into a hopper in a covered breezeway. Everyone is careful and 99.99% of the weed seeds make it directly into the hopper. In spite of the care taken, two hundred weed seeds remain in the bottoms of the containers and on the unloading dock. A conscientious inspector vacuums out the containers and verifies that everything went according to plan. She sweeps the small quantity of soybeans from the edge of the concrete slab into the hopper. She is good—in fact, she is 99% effective. Now only two weed seeds remain, plus several more in the vacuum bag. Months later, the vacuum bag becomes full and is thrown in the trash. On garbage day, it is picked up and hauled to the landfill where it is buried. After a couple of decades, all those seeds are dead.

         Meanwhile there are still two viable weed seeds in play. One of them is lodged in the hinge of a container; the other was on the concrete slab surrounding the grain hopper before it stuck briefly to a trailer tire and got moved to the processing plant driveway. It remains for a month until it is washed into the ditch during a rain shower.

         The other seed is lodged in the container door hinge. It travels the world but remains stuck under some rust. Sometime later the container is sandblasted and the seed dies. Now there is only one seed left. After being washed downstream, it settles out where the water collects when the ditch dries up. Weeds grow up in the ditch, and the dodder seed germinates. It is a parasitic plant that latches on to other plants and gets its nutrients from them. It looks like a stand of spaghetti. Nobody notices it twined around its host. That year the dodder plant flowers and produces 200 seeds. Some of them are washed further downstream the next winter. Earthworms and other little critters eat some and poop them out where they wander. After a few years, there is a small patch of dodder plus a couple of satellite patches some distance away. The total dodder seed bank is now up to 10,000 seeds each capable of remaining viable for a decade or more.

         A road maintenance employee sees the weeds and sprays over the patch. Almost all (99%) of the dodder plants are killed. But because of the seed bank, dodder returns next year and the year after that, and each year there is more, and it spreads. Some years later, a farmer notices the unfamiliar weed in his field and calls in an expert from Oregon State University. They identify it immediately as Cuscuta sp., and take a sample for further analysis. Everyone is baffled when it is identified as a species from China never before seen in the United States. ODA is notified, and conducts an investigation and a weed risk assessment. Agency staff debates attempting to eradicate this new threat to Oregon’s agriculture and natural resources. The long lived-seed is a problem, and chances of successful eradication are low. No one involved makes the connection to the contaminated soybean shipment that arrived 15 years ago. A new weed has established in Oregon.

         This scenario is not going to play out this time, at least not in Oregon. We don’t think it is possible to contain 2 million specks of dust in 500 tons of soybeans.

         As I write this, the containers are still sitting on the dock in Portland, and the importer is trying to find another state that will accept them and a transportation/processing procedure USDA will approve. Fifty-two more containers of organic soybeans are en route from China.

         If you’re wondering why the United States, the largest producer and a major exporter of soybeans, is importing soybeans, you’re not alone. Ships containing soybeans must pass each other on the oceans going opposite directions. Globalization makes for crazy trade patterns—and efficient transport of invasive species. This story is getting depressing, I think I’ll go eat something—maybe I’ll BBQ those organic chicken breasts.

Dan Hilburn

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