THE CONCEPT AND APPLICATION OF EARLY ECONOMIC PERIOD THRESHOLD - THE CASE OF DCPA IN ONIONS (ALLIUM-CEPA)

The question of when to control weeds traditionally has been approache d with the calculation of critical periods (CP) based on crop yields, The concept of economic critical period (ECP) and early (EEPT) and lat e (LEFT) economic period thresholds are presented as a comprehensive a pproach to answer the same question based on economic losses and costs of control. ECP is defined as the period when the benefit of controll ing weeds is greater than its cost, EEPT and LEFT are the limits of th e ECP and can be used to determine when first and last weed control me asures should be performed, Calculation of EEPT accounts for the econo mic losses due to weed competition that occur between planting and pos temergence weed control, In this way it is possible to better evaluate the economic feasibility of using preplant or preemergence control ta ctics, The EEPT for DCPA application is analyzed in the context of oni on production in Colorado, The EEPT for DCPA application was calculate d from an empirical regression model that assessed the impact of weed load and time of weed removal on onion yields, The EEPT was affected b y control efficacy, weed-free yield, DCPA cost, and onion price, DCPA application was economically advisable in only one of 20 fields analyz ed because of the low DCPA efficacy (60%).