Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
12/2/02
Contacts:
Paula Flynn, Plant Pathology, (515) 294-0581, pflynn@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning Dec. 6, 2002
Holiday Food Foes
By Paula Flynn
Extension Plant Pathology
Iowa State University
Good food is one of the focal points of the holiday season. Chestnuts, sweet potatoes, homemade fruit pies and apple cider come to mind as a few traditional favorites. These favorites have one thing in common - they all came from plants.
We might assume these plants were started as seeds, grew vigorously in the soil with the help of the sun and a knowledgeable farmer, were harvested when they were mature, and were then sent off to the produce aisle at our grocery store.
The road to our dining table, however, may have not been an easy one. Plants and farmers had to ward off hungry foes that wanted to feast on the crops before they made it to our homes. Some of these thieves are too small to see with the naked eye, making them especially difficult to guard. Microscopic fungi, nematodes, bacteria and viruses, collectively known as plant pathogens, sometimes get to our food before our friends and family.
Most of us know the song "Chestnuts roasting on an open fire." There are fewer chestnuts to roast since the introduction of the chestnut blight fungus into our country. The disease was first detected in New York City in 1904 and had a devastating effect on American chestnut trees. Because the fungus was new to our country, native trees didn't possess natural resistance to the fungus. The chestnut blight fungus enters trees through wounds and grows under the bark, eventually working its way around branches and causing them to die. Almost 100 years later we're still struggling to save our remaining American chestnut trees. Recent research has offered glimmers of hope. A "good" strain of the fungus has been found that seems to stop or slow the disease when injected into the diseased chestnut trees. In addition, breeding programs are striving to develop trees that are able to fight off the fungus.
With their bright orange color, sweet potatoes make their way to the front of the table during the holidays. Sweet potatoes have a long list of problems to battle, and the root-knot nematode is one of the most destructive. This microscopic, worm-like creature makes a home in the roots of sweet potato plants. The common name of root-knot describes the appearance of the roots. They develop small swellings. The large storage root develops blister-like bumps. With the root system under siege, the aboveground part of the plant usually looks sickly, showing yellow, wilting leaves and poor growth. One of the main ways to control the root-knot nematode is to rotate planting to a new area and plant other crops in the problem field. This approach can be difficult, however, because the nematode attacks many different types of plants.
Warm apple cider and homemade apple pie are good ways to start and finish a holiday meal. Fire blight, a destructive disease on apples, is caused by a bacterium. Flowers, twigs, large branches, trunks and fruit can be killed. The ends of infected twigs typically wilt and turn black, taking on a burned appearance. These downward-bending branch tips are sometimes called shepherd's crooks. Infected fruit typically shrivel and turn black. When conditions are humid, a cream-colored bacterial ooze often occurs on the surface of infected plant parts. The disease is controlled by carefully pruning out the diseased areas of the tree during the winter. Certain apple varieties are moderately resistant to the disease. Some growers carefully monitor the weather and apply protective antibiotic sprays when conditions are conducive for a severe outbreak.
There are many more examples of favorite holiday foods and the problems they face as they grow in the field or orchard. Sometimes disease problems are severe enough that there is no harvest. Otherwise, the yield may be reduced or the product may simply show a blemish or two. So as we sit down to enjoy our holiday meals our thoughts might momentarily turn to the plant variety that was able to resist the pathogen, the farmer who had the expertise to grow a healthy crop and the plant pathologist who worked to discover new ways to control or avoid a plant disease problem.
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