Feed-Value Approach for Establishing Economic-Injury Levels

Abstract

Forage pest management has been less amenable to the use of economic-injury levels as decision guides than have cash crops. One reason for this incompatibility is the lack of a common exchange market for forages and their on-farm production as a nutrient source for livestock or dairy production. Least-cost rationing (based on linear programming techniques), however, provides a method of estimating the utility of forages within a multi-feed ration to provide a representative monetary value for use in calculating feed-value economic-injury levels. Because animals differ in their ability to physiologically utilize forages as feed, specific economic-injury levels can be determined for specialized dairy or livestock production circumstances. Least-cost rations were calculated using data for feed nutrition and animal requirements based on representative production goals for dairy cows (3 types), beef cows and steers, sheep, and horses. The objective was to determine the relative value of alfalfa to the total feed ration for each animal class and thereby design a production-specific forage pest management system. Least-cost rations selected from 6 possible feed choices determined the feed-value of alfalfa grown on-farm, and these data were used to calculate economic-injury levels for potato leafhopper, Empoasca fabae (Harris), for each animal production system. Results demonstrate that horse and sheep production have the lowest economic-injury levels, whereas beef steers have the highest. The magnitude of difference was 129%, with dairy- and beef-producing cows having intermediate levels. The magnitude of difference in the economic-injury levels among animal types clearly demonstrates the need to refine forage economic-injury levels based on the utility of the crop to the final feed-value to the animal consumer. Least-cost rationing provides one way of accomplishing this refinement.