Continuing Education and
Communication Services
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
12/3/01
Contacts:
Mark Gleason, Extension Plant Pathology, (515) 294-0579, mgleason@iastate.edu
Del Marks, Continuing Education and Communication Services, (515) 294-9807,
delmarks@iastate.edu
Yard and Garden Column for the Week Beginning Dec. 7
Plant Diseases Go Global
By Mark Gleason
Extension Plant Pathologist
Iowa State University Extension
"Globalization" could be today's most abused buzzword. It seems that everything that was once local, from societies to trade to politics, is now either global or soon will be.
As a university faculty member, I am too sheltered and unworldly to know whether globalization is generally a good thing, a bad thing or both. But in the realm of plant diseases -- my own narrow focus -- globalization has definitely arrived. And it will keep plant pathologists and farmers worried about protecting food, fiber and ornamental crops throughout the crowded 2lst century.
Globalization of plant diseases has little to do with agri-terrorists but everything to do with us. Exotic plant diseases arrive at our front door with ever-increasing frequency because the volume of plant materials shipped from exotic foreign locales is skyrocketing. This flood of imported plant material includes not only such consumer items as fruits, vegetables, seeds and transplants, but also obscure ones such as pallets and packing crates. Hitchhiking with a small percentage of all this stuff come the fungi, bacteria, viruses and nematodes that cause plant diseases.
Most of these microbial riffraff pose no threat to our plant life. For example, fungi that cause banana diseases in Central America aren't likely to impact any crops in Iowa. And many foreign microbes are dead on arrival thanks to chemical fumigants, fungicide dips and simply the passage of time since their plant hosts were harvested.
But a few hardy, or lucky, microbes survive their ordeal in steerage and find golden opportunities for infecting plants in America. The result can be crop-destroying epidemics that catch everyone by surprise.
Examples of such transcontinental leaps abound. Today, almost all of the hybrid tomato seeds planted in the United States are grown by hundreds of small-scale farmers in China, India and other Asian countries. The reason is that the labor required to make hybrid seeds is cheaper there than elsewhere. A small number of these seeds can be infested with the bacteria that cause a devastating tomato disease known as canker. Once the infested seeds germinate and grow in an American greenhouse, the bacteria latch onto the seedlings and splash to neighboring plants whenever the crop is watered, so that just a few infested seeds can result in hordes of infested seedlings. After transplanting to outdoor fields and gardens, canker takes over and the seedlings wilt like last week's lettuce.
Daylily rust appeared in the United States for the first time last summer. It seems that a daylily grower in Costa Rica shipped plants to a Florida nursery, that then proceeded to resell them to retailers all over the United States. A few weeks later, reports began to filter in from state after state -- including Iowa -- of rusty-colored streaks and yellowed leaves. It turns out that the plants had contracted a whopping case of daylily rust. Daylily rust is caused by a fungus that was previously unknown on daylily, but probably came to Costa Rica from Asia. Daylily fanciers now worry that this illegal alien may be an annual plague on American daylilies.
The flow of plant-killing microbes is not an anti-American conspiracy, since we have unwittingly returned the favor many times. For instance, a nematode (microscopic-size worm) shipped on U.S. logs to Japan has decimated native Japanese black pine and red pine forests since the 1970s.
Why can't these plagues be blocked at our borders, or better yet before they arrive here? One problem is that the culprits are too small to see with the naked eye. So the challenge is to detect something you can't see. If this sounds much more expensive and difficult to do than mere visual inspection, it is.
Another problem is the overwhelming volume of foreign plant material that lands here every day. The federal agency charged with inspecting all this stuff, the Animal and Plant Health Inspection Service (APHIS), is in the same position as the kid trying to keep his finger in the dike while water gushes in everywhere. APHIS does heroic work, but there is simply too much plant material and not enough inspectors. Without APHIS the plant disease invasion would be far worse, but only a tiny fraction of the incoming plant material ever gets viewed or analyzed.
Is the globalization of plant disease a cause for despair? Certainly not for plant pathologists, since it boosts our job security. But for farmers and gardeners, it's likely that new diseases will appear with increasing frequency, as a form of collateral damage that shadows the many benefits of burgeoning international trade.
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ml: isugarden
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