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Social Impact and Economic Importance of Late Blight

The potential economic and social impact of this disease is best illustrated by the well-publicized role it played in the Irish Famine in the middle of the 19th century.  Irish peasants depended on the potato for their primary source of calories.  When blight arrived in the mid 1840s, it destroyed a large portion of the potato crop, either by eliminating foliage prior to the harvest or by causing massive tuber rot in storage.  As a result of the famine, millions of Irish died or emigrated (Bourke, 1993). 

The huge social consequences of blight in the 1840s also led to major scientific advances.  At this time there was a debate among scientists whether plant diseases were caused by fungi or vice versa.  Most believed that plant diseases occurred spontaneously and fungi followed, saprophytically, as a consequence (Peterson, 1995).  As a result of investigations into the cause of late blight by Berkeley in England (Nelson, 1995), and De Bary and Kuhn in Germany (Peterson, 1995) the idea of germ theory for plant diseases was generally accepted.

Late blight is a very serious economic threat in the vast majority of potato production systems, as well as many tomato production systems worldwide.  In locations where disease pressure is high, a susceptible potato variety may require fungicide applications every 3 – 5 days.  In spite of the obvious destructive potential of late blight, it is extremely difficult to measure losses due to this plant disease because other factors simultaneously affect yield (Madden, 1983).  For that reason, many of the published references to crop loss caused by potato late blight are based on estimates made by local experts who extrapolate from field trials or visits to farmers fields (Table 1).  While this approach is imperfect, it is often the only information available for certain parts of the world.  

In some cases, economic losses due to potato late blight were analyzed systematically. For one epidemic occurring in 1995 in the Columbia Basin of the state of Washington in the US, the mean number of fungicide applications per field varied from 5.1 to 12.3, depending on cultivar.  Total per acre expenses (application costs plus fungicide material) ranged from $106.77 to $226.85 and the total cost of managing late blight was estimated to have approached $30 million (Johnson et al., 1997).  In a national assessment, the economic impact of potato late blight in all of the USA was estimated to be about $210 million (Guenther et al., 2001).  The International Potato Center  (CIP) has made a global estimate of late blight damage in developing countries based on an average production loss of 15%.  This translates into a total production loss in developing countries of approximately $2.75 billion (Anonymous, 1997). 

One important way of viewing the economic effects of potato late blight is by assessing fungicide usage, which is easier to measure than crop loss.  About $77 million are spent on fungicides per season throughout the US (Guenther et al., 2001).  Yearly fungicide usage for late blight control in Europe is estimated to be about $150 million (H. Schepers, personal communication).  CIP estimated fungicide use in developing countries at $750 million (Anonymous, 1997).  Based on these estimates, about $1 billion per year is spent on fungicides to control late blight in the US, Europe and developing countries.  Two recent studies put the total loss (direct and through fungicides) at between $3 and $5 billion per year (Judelson and Blanco, 2005; Haldar et al, 2006). 

P. infestans is also a very important pathogen of several other cultivated solanaceous hosts, including tomato (Solanum lycopersicum), pear melon (S. muricatum), naranjilla (S. quitoense) and tree tomato (S. betaceum).  Unfortunately, we know of no quantitative accounts of the damage done to these crops, although global damage to tomato due to late blight is immense.  Fields of pear melon are sprayed frequently against late blight, but still suffer heavy damage during rainy weather (first author's personal observation).  Most pear melon cultivars appear to be very susceptible.  The area of cultivation of tree tomato is limited in parts of Ecuador due to late blight.  For example, in the valley of San Jose de Minas, Imbabura, the crop was virtually abandoned because of late blight. 

Table 1.  Selected references indicating degree of loss due to late blight in different locations 


Estimated loss due to late blight



6-40 %

(Cupsa et al., 1983)



(Pietkiewicz, 1991)


Up to 40%

(Higiro and Danial, 1994)


Up to 65%

(Rao and Veeresh, 1989)
(Bisht et al., 1997)


25-75 %

(Fontem and Aighewi, 1993)

Literature Cited

Anonymous (1997). "CIP in 1996. The International Potato Center Annual Report." , International Potato Center, Lima, Peru. 59pp.

Bisht, G.S., S. Harish, and H. Singh. (1997). Fungal diseases of useful plants in the Garhwal Himalaya and their management, p. 255-271. In: S.C. Sati, J. Saxena, and R.C. Dubey (eds.). Himalayan Microbial Diversity. Today and Tomorrow's Printers & Publishers, New Delhi, India.
Bourke, A. (1993). 'The Visitation of God'?  The potato and the great Irish famine. Dublin, Ireland., Lilliput Press, Ltd.
Cupsa, I., I. Ignatescu, and E. Vogel. (1983). An epidemic of potato late blight in 1982, and measures taken to prevent it in 1983. Epidemia de mana a cartofului in anul 1982 si masuri de prevenire a acesteia in anul 1983. Productia-Vegetala,-Horticultura 32: 22-26.
Dowley, E. Bannon, L. R. Cooke, T. Keane and E. O'Sullivan. Dublin, Boole Press: 1-11.
Madden, L. V. (1983). "Measuring and modeling crop losses at the field level." Phytopathology 73(11): 1591-1596.
Fontem, D.A. and B. Aighewi. (1993). Effect of Fungicides on Late Blight Control and Yield Loss of Potato in the Western Highlands of Cameroon. International Journal of Pest Management 39: 152-155.

Guenther, J. F., K. C. Michael, et al. (2001). "The economic impact of potato late blight on US growers." Potato Research 44: 121-125.

Haldar, K., Kamoun, S., Hiller,  N. L., Bhattacharje S and van Ooij, C. (2006) Common infection strategies of pathogenic eukaryotes. Nature Reviews Microbiology 4, 922-931

Higiro, J. and D.L. Danial. (1994). Potato production in Burundi: constraints and research. In: Proceedings of   a regional workshop for eastern, central and southern Africa. Proceedings of a regional workshop for Eastern, Central and Southern Africa, Njoro, Kenya. p. 117-118.
Johnson, D. A., T. F. Cummings, et al. (1997). "Potato late blight in the Columbia basin: an economic analysis of the 1995 epidemic." Plant Disease 81(1): 103-106.
Judelson,  H. S. and  Blanco,  F. A. (2005) The spores of Phytophthora: weapons of the plant destroyer. Nature Reviews Microbiology 3, 47-58

Nelson, E. C. (1995). The cause of the calamity: the discovery of the potato blight in Ireland, 1845-1847, and the role of the National Botanic Gardens, Glasnevin, Dublin. Phytophthora infestans 150. L. J.

Peterson, P. D. (1995). The influence of the potato late blight epidemics of the 1840's on disease etiology theory in plants. Phytophthora infestans 150. L. J. Dowley, E. Bannon, L. R. Cooke, T. Keane and E. O'Sullivan. Dublin, Boole Press, 30-35.

Pietkiewicz, J.B. (1991). Potato production and protection in Poland in the 1990s. Bulletin-OEPP 21: 1-7.

Rao, A.N.S. and G.K. Veeresh. (1989). Estimation of yield loss due to late blight in rainfed potato. Current-Research---University-of-Agricultural-Sciences-Bangalore 18: 157-158.