While there are large numbers of site, time, pest, and crop specific yield loss reports, there are few attempts to estimate global crop losses. Among these, the efforts of Cramer (1967) and Oerke et al. (1994) deserve recognition. During the time between Cramer (1967) and Oerke’s et al. (1994) assessments, Pimentel (1978) made another attempt to estimate losses of world food crops due to pests. However, his estimates were essentially the same as Cramer’s (1967) as he mainly used Cramer’s percent loss data, then calculated quantities of loss based on production during the early to mid 1970's.
Cramer published the first global estimate of crop losses due to pests in 1967. He considered large number of crops such as wheat, rice, maize, other cereals, potatoes, sugar beet and sugarcane, vegetables, fruit crops, stimulants, oil crops, fiber crops, and natural rubber. He first assessed actual production, then calculated loses due to insect pests, diseases and weeds based on available data. Next, he added actual production and losses due to pests to derive potential production. Cramer considered the difference between potential production and actual production as crop loss. He estimated that the global annual pre-harvest losses of all crops to be approximately 34.9% of their potential production. Of the 34.9%, 13.8% was due to insect pests, 11.6% was due to diseases, and 9.5% was due to weeds (see below, Figure 3).
Figure 3 - Global losses of food, fibe,r and cash crops due to insect pests, diseases and weeds (Cramer, 1967).
Oerke, et al. (1994) published another global estimate of losses for eight major food and cash crops such as rice, wheat, maize, potatoes, cotton, soybean, barley, and coffee. Their estimate also used a more or less similar approach as that used by Cramer in 1967. They calculated country and regional attainable productivity and actual production using data for 1988-90 from the FAO. Potential and actual losses were estimated by assembling published yields and crop loss data, or if not available, by extrapolating country or regional data with similar agronomic conditions. Their estimates indicated that the pre-harvest losses due to pathogens, animal pests, and weeds for the eight major crops were 42% of the attainable yield for 1988-1990.
Of the 42%, 16% was due to insects, 13% to diseases, and 13% due to weeds (Figure 4). A further 10% post-harvest loss amounted to a total pre-and post-harvest loss of 52%. Loss data of Cramer’s (1967) can be compared directly to that of Oerke et al. (1994). However, it must be remembered that Cramer (1967) grouped viral diseases with other diseases, while Oerke et al. (1994) grouped them under animal pests since vector insects transmit viruses.
Figure 4 - Global losses of eight major food and cash crops of the world (rice, wheat, barely, maize, potatoes, soybean, cotton, and coffee) due to animal pests, pathogens, and weeds (Oerke, et al. 1994).