DATE:    3/8/01 
WRITER:  Dr. Tony Keinath, Clemson Extension plant pathologist, 
         (843) 766-3761
EDITOR:  Giles Singleton, (864) 656-3876

St. Patrick's Day and the Irish Potato Famine

     CLEMSON -- St. Patrick's Day celebrations have deep Irish 
roots. Many Irish people left Ireland for the United States because 
of the Irish Potato Famine in the mid-1840's. Today the plant 
disease that caused the famine is back, and this time it's even
stronger.
     "My guess is, we probably wouldn't celebrate St. Patrick's Day 
in the United States if the Irish Potato Famine had not happened," 
said Tony Keinath, Clemson Extension Service vegetable pathologist.
"Late blight of the Irish potato is probably the most famous plant
disease in the world -- not just because it caused the Irish Potato
Famine, but because it is a problem again today." 
     The Irish Potato Famine occurred in 1845 and 1846 when the 
potato crop in Ireland was destroyed by late blight. Because most 
Irish were tenant farmers for English landlords, they used their 
grain and other crops to pay the rent. They themselves ate mostly
potatoes, which were very productive in the cool climate.
     Unusually wet and cool weather in the summers of 1845 and 
1846 created ideal conditions for the late blight fungus to grow 
and spread quickly. As a result of late blight, famine and then 
disease devastated the country. Historians call this period the 
Great Irish Famine of 1845-1852, because it took several years for 
the local economy to recover.
     The science of plant pathology -- the study of plant diseases 
and how to control them -- also goes back to the Irish Potato 
Famine.  A German scientist named Anton deBary studied potato late
blight and found it was caused by a fungus. However, his discovery
wasn't made until 1861, too late to save the Irish potato crop.
     Most scientists believe that late blight originally spread in
potato tubers from Mexico via the United States to Europe. Recently,
late blight traveled from Mexico to Europe, but this time it was a 
more dangerous form of the fungus, the A2 strain. This strain was 
found in Europe in 1984, in the United States in 1987, and in South
Carolina in 1994.  
     The A2 strain causes late blight faster and likes warmer 
temperatures than the old A1 strain. It also cannot be controlled 
with the standard fungicide used for almost 15 years. Most troubling
for home gardeners, it seems to attack tomatoes almost as often as
Irish potatoes.
     Dry periods during recent springs have kept late blight from 
being a problem in South Carolina. However, late blight occurs in
Florida on winter potatoes and during most summers in all of the 
major potato-growing areas of the country.  Late blight is found
throughout the Midwest on commercial tomatoes. Fresh market tomatoes 
in the mountains of North Carolina and in California can also have 
late blight.
     To combat late blight, breeders are working with wild relatives 
of Irish potato and tomato to make new vegetables blight resistant.
Chemical companies have designed new fungicides that stop the A2
strain. Pathologists are re-emphasizing the age-old practice of
destroying infected crops, especially potato tubers left on the 
ground, which can harbor the fungus until the next crop.
     "If the Irish peasants had known that the late blight fungus 
would survive in potato tubers and had destroyed them after the 
1846 crop failure, maybe blight wouldn't have been as bad in 1847,"
Keinath said.
                     **********************
     If you have questions or comments on gardening, write to PSA 
Media Relations, A-101 Poole Agricultural Center, Clemson University,
Clemson, S.C. 29634-0129.
     You might also want to look for other "Buds and Blooms" columns
under 2001 News Releases at: www.clemson.edu/psamedia.
                              END