Assessment of Plant Diseases and Losses

Plant diseases were initially studied because of the losses they cause, yet today it is paradoxical that there are only a few reliable estimates of loss. In 1918 Lyman (67) stated, How can we expect practical men to be properly impressed with the importance of our work and to vote large sums of money for its support when in place of f acts we have only vague guesses to give them and we do not take the trouble to make careful estimates. During the last decade we have witnessed more interest in disease-loss appraisal because of the need to develop more sophisticated disease management schemes that must justify and rationalize the use of fungicides. Fund­ ing organizations have also been operating on limited budgets and have required more convincing evidence before supporting research programs. International con­ cern about the inadequacy of present methods for assessing diseases and estimating losses resulted in FAO's sponsoring a Symposium on Crop Losses in 1967 (26) which recommended development of more precise methods (27). so that the limited expertise available could be deployed in the most efficient way. In a world conscious of pollution, loss estimates may achieve new significance by providing evidence that will justify or condemn the use of fungicides to control epidemics. To develop rational and economical control measures, whether by breeding resistant cultivars or using fungicides, it is not sufficient to state that disease causes a loss; the magni­ tude of the loss must be evaluated so that it can be related to the gain obtained. Only by disease-loss appraisal is it possible to determine the economic loss due to different amounts of disease. Disease-loss appraisal therefore represents an absolutely essen­