In the article, the researchers explained a two-pronged problem: Why it is difficult to detect low levels of late blight in a field and how the fungus reproduces rapidly. The late blight disease cycle of penetration, colonization, sporulation and dispersal can occur in less than five days. The researchers note that each individual late blight lesion can produce as many as 300,000 sporangia a day. Some infected tubers may be destroyed before harvest, but with a multiplicity of virulent spores, harvested potatoes can easily become diseased in storage. Bacteria that cause soft-rot diseases often invade potato tubers infected with late blight, literally resulting in a "meltdown" of stored potatoes. Under severe infection, entire storages have to be discarded.
Scientists began noticing late blight's resistance to metalaxl as long ago as 1980, Fry says. The fungicide is the only way to salvage crops infected with late blight. Other available fungicides are only effective when applied before late blight strikes. Many agriculturists consider such treatment as ineffective against the disease.
In the article, the researchers note that the short-term response has been to use more fungicide. Other solutions, such as developing disease resistant varieties, they say, could be five to 15 years away from introduction.
The article, "Re-emergence," appears in Plant Disease (Vol. 81, Number 12, pages 1349-1357, December 1997.) Fry and Goodwin also co-authored an article, "Resurgence of the Irish Potato Famine Fungus," in the journal BioScience (June 1997).