Crop Losses Associated with Grasshoppers in Relation to Economics of Crop Production1

Abstract

Grasshopper population estimates from an annual grasshopper survey were interfaced with crop-yield estimates and weather information to provide a quantitative assessment of the impact of grasshoppers on Saskatchewan agriculture. Two multiple regression models were developed to estimate yields of wheat, oats, and barley on an individual district basis during a 32-yr period (1943–74). One model included year, precipitation, and a heatprecipitation ratio; the other incorporated grasshoppers as an additional variable. The model including grasshoppers explained a higher proportion of the variance than the model without grasshoppers. Estimates of crop yield from the regression models were used to develop a model of yield loss caused by grasshoppers for each of the 3 crops. The economic impact of grasshoppers on wheat production was evaluated by using estimated losses based on actual crop prices and indexed costs related to production and crop protection. Results showed that losses caused by grasshoppers were dynamic but small relative to dynamics of crop price and yield losses independent of grasshoppers. Economic losses caused by grasshoppers tend to occur when economic gains are otherwise depressed because of poor crop yields due to drought or low crop prices. In 1961, in spite of extensive measures taken to protect the crop from grasshopper depredation, loss in wheat production due to grasshoppers was estimated to have been $40 million, representing ca. 17% of the value received for wheat. Wheat yields in 1961 were 0.565 T/ha (8.4 bu/acre) compared to the 20-yr avg of 1.425 T/ha (21.2 bu/acre). The avg probability of economic loss in Saskatchewan (all districts during 1943–74) was 0.48, 0.72, and 0.32 for wheat, oats, and barley, respectively, based on 1976 prices and costs, with the highest chance of loss occurring in the southwestern region of the province. Since a high probability exists both of having drought and high grasshopper populations in the southwestern region, it is wise to consider reducing small-grain production there and growing other crops instead.