Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Re-Emergence of Potato and Tomato Late Blight in the United States and Canada

Authors
item Fry, William - CORNELL UNIVERSITY
item Goodwin, Stephen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 30, 1997
Publication Date: N/A

Interpretive Summary: Recent migrations of the potato/tomato late blight pathogen, Phytophthora infestans, have worsened a disease that had been effectively controlled for decades in the States and Canada. During 1993-1995, late blight was the largest constraint to potato and tomato production in many parts of America north of Mexico. Some growers lost their entire crop and were subsequently yforced out of business. These problems were caused mostly by a single new clone of the fungus, called US-8, that was probably introduced from Mexico during the early 1990s. This clone is resistant to the fungicide metalaxyl which previously had provided almost complete disease control. In addition to fungicide resistance, the US-8 genotype is much more aggressive than previously existing genotypes. It causes larger lesions on leaves and tubers and kills tissue faster than did the genotypes that were present before the most recent migrations. Analyses of where and when new genotypes were identified reveals the speed of the recent migrations. The US-8 genotype was first detected in one state during 1992, but by 1994 was found throughout the United States and in several provinces in Canada. The speed of these migrations could not have been predicted, and made it impossible for them to be stopped. Growers and plant pathologists alike were surprised by these migrations, and must now deal with a heightened threat of disease. Recent meetings sponsored in part by the USDA have generated a series of recommendations for combating the problem. It is hoped that these recommendations will lead to improved disease management strategies. The purpose of this paper was to increase awareness of the speed and consequences of the recent migrations, so that potato/tomato growers and industry will be better prepared in the future.

Technical Abstract: Recent migrations of the potato/tomato late blight pathogen, Phytophthora infestans, have worsened a disease that had been effectively controlled for decades in the States and Canada. During 1993-1995, late blight was the largest constraint to potato and tomato production in many parts of the United States and Canada. Some growers lost their entire crop and were subsequently forced out of business. These problems were caused mostly by a single new genotype, US-8, that was probably introduced from Mexico during the early 1990s. This genotype is resistant to the fungicide metalaxyl which previously had provided almost complete disease control. In addition to fungicide resistance, the US-8 genotype is much more aggressive than previously existing genotypes. It causes larger lesions, faster, and is more efficient at rotting potato tubers. Analyses of temporal and geographical distributions of genotypes revealed the speed of the recent migrations. The new genotypes were first detected during 1992, but by 1994 were found throughout the United States and in several provinces in Canada. The speed of these migrations could not have been predicted, and made it impossible for them to be stopped. Growers must now deal with a heightened threat of disease. Recent meetings sponsored in part by the USDA have generated a series of recommendations for combating the problem. It is hoped that these recommendations will lead to improved disease management strategies in the future.

Last Modified: 10/25/2014
Footer Content Back to Top of Page