An evaluation of insecticide and nitrogen fertility programs in dry bulb onions in the treasure valley of Eastern Oregon and Southwest Idaho in 2019 to 2021.

Field studies were conducted at Oregon State University, Malheur Experiment Station, Ontario, Oregon, from 2019 to 2021 for evaluation of optimal use of insecticides and in-season nitrogen fertilization to maximize profitability of dry bulb onion production. Insecticide programs included a control, a calendar-based weekly program, and an action threshold-based integrated pest management program. Nitrogen fertility was evaluated at two levels, standard and reduced. The standard nitrogen fertility program was based on recommended rates determined from soil and tissue tests. The reduced program delivered nitrogen at 50% of the recommended amount. Results pertaining to optimal use of insecticides were inconclusive. Each year of the study resulted in a different outcome relating to best practices for timing and delivering insecticide applications, indicating the need for more research. Standard nitrogen fertilization programs optimized profit in all 3 years of the study. The greater overall profitability of the standard fertilization program provides evidence to support using and following recommendations from soil and tissue tests for economically advantageous management of in-season nitrogen fertilization of dry bulb onions. The relative value of benefits from every dollar spent on nitrogen fertilizer during each year of the study was also evaluated using benefit-cost ratios. Even when the price of nitrogen was high relative to the value of the crop, investment in nitrogen still produced positive economic benefits.