Introduction - Disease Control in Crops - page 1

Chapter 1
Introduction

Dale Walters
Scottish Agricultural College, Edinburgh, UK

1.1
Plant disease has been a continual problem for mankind ever since the beginnings of
agriculture some 10 000 years ago. These problems persist, despite the advent of
fungicides and resistant varieties, due to the genetic adaptability of the pathogens which
cause plant disease. Although crop losses at farm and local level can have serious implica-
tions for growers, plant disease can infl ict much more serious damage on a larger scale.
The often-cited potato blight epidemic of the 1840s in Europe is an example of how
devastating plant disease can be. This disease, caused by the Oomycete pathogen
Phytophthora infestans, decimated crops across Europe, and in Ireland, led to the death
of some one million people and the emigration of several million more (Large, 1940;
Strange, 2003). Incredibly, today, more than 170 years later, potato blight still poses a
major problem for potato growers across the globe. The devastation caused by potato
blight is but one example of the damage plant diseases can infl ict on mankind. Thus, in
the Great Bengal Famine of 1943, the fungal pathogen Cochliobolus miyabeanus devas-
tated rice crops and led to the starvation and death of an estimated two million people
(Padmanabhan, 1973), while in Ceylon (now Sri Lanka), the arrival of the rust fungus
Hemileia vastatrix in 1875 heralded the beginning of the end of coffee growing on that
island. Here, coffee rust had virtually wiped out coffee plantations by 1889, forcing the
islanders to switch to growing tea (Schumann, 1991).

The importance of plant disease

1.1.1 Crop losses due to disease

It might be expected that given the historical importance of plant disease in arable
agriculture, accurate estimates of crop losses as a result of disease would be readily
available. In reality, the availability of quantitative data on the effects of pathogens on
crop losses is very limited (Oerke, 2006). This should not be surprising, since as pointed
out by Oerke (2006), the generation of such data is laborious and time-consuming and
to complicate matters, crop losses will vary between seasons because of variations in
pathogen incidence and disease severity.
Crop loss as a result of disease can be expressed in absolute terms (e.g. kg ha 1 )
or relative terms (e.g. % loss), while the loss rate can be expressed as the proportion
of attainable yield, although the proportion of the actual yield is sometimes used