Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
12/30/02
Contacts:
Barbara Ambruzs, Plant Pathology, (515) 294-1741, ambruzsb@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning Jan. 3
Insects and Fungi with a Taste for Champagne
By Barbara Ambruzs
Extension Plant Pathologist
Iowa State University
Champagne glasses clinking at the stroke of midnight on New Year’s
Eve will hide a secret tale. The grapes crushed to make the festive drink
hold a story of mold and mischief. It includes thieves, two fungal diseases,
an insect and two Frenchmen.
In the early 1800s powdery mildew caused problems for French champagne
grape growers. Powdery mildew is a common fungal disease that affects
just about every kind of plant. There are many different species of powdery
mildew, so each species is somewhat specific to the type of plant it will
infect. For example, the powdery mildew fungus that infects lilac isn’t
the same species that infects turfgrass.
French breeders thought it would be a good idea to import powdery mildew-resistant
grapes from the United States. However, in doing so they imported an even
more devastating pest called phylloxera, an insect that feeds on grape
roots. This insect wasn’t a problem in the United States because
the grape varieties in this country developed natural defenses over time
as they evolved together. French grapes had no defense against this pest.
To get around this problem, plant breeders grafted French grape vines
(the top of the plants) to the roots of resistant grapes from the United
States. This grafting worked splendidly. The French were able to grow
grape varieties that had special qualities for making great champagne
and also had resistance to powdery mildew and phylloxera.
However, an even more devastating problem was imported with the United
States grape roots. Downy mildew.
Downy mildew seriously impacted French grape production during the late
1800s. Leaves affected by downy mildew develop pale yellow-green spots
on the upper surface and white web-like fungal threads develop on the
underside. Grapes shrivel and become useless. Losses amounted to nearly
$50 billion in France during this time.
The downy mildew fungus uses stomata (tiny pores that allow for gases
to pass in and out of leaves) as doorways to get in and out of the plant.
Many plants have most of their stomata on the bottom of their leaves.
That’s why downy mildew is usually seen on the underside of leaves.
Powdery mildew gets into cells on its own with the help of enzymes, proteins
that speed up chemical reactions.
One French farmer had another pesky problem in his vineyard. His pests
were of the human kind. Those walking by would help themselves to a refreshing,
tasty snack of grapes along their way. The clever farmer sprayed a concoction
of copper sulfate and lime on the fruit. No one wanted to eat the bluish-coated
grapes. They looked poisonous. So his profits weren’t eaten.
Alexis Millardet, a French plant scientist, traveled along the same road
on his way to and from work. He noticed that the vines coated with copper
sulfate and lime along the path weren’t dying from downy mildew.
In fact, the bluish coating seemed to protect them, while untreated plants
were sickened by downy mildew. Today, this combination of copper sulfate
and lime is known as Bordeaux mixture. It is just as effective now as
it was in Millardet’s day.
Thanks to the botanist, the farmer and a host of plant breeders there
are defenses against insect and disease pests. Champagne grapes are still
grown in France and even here in Iowa.
-30-
ml: isugarden
Extension programs are available to all without regard to race, color, national origin, religion, sex, age, or disability.