Mechanical covering to prevent shoulder greening in white onions

Abstract

Onion (Allium cepa L.) varieties 'Contessa', 'White Early Supreme', 'Texas Grano 1015Y' (TG 1015Y), and 'Perla' were utilized in field studies that were conducted in 1988 and 1989 in Rio Grande City, College Station, Weslaco and Lubbock, Texas. Covering at six, four, and two weeks before harvest, and no cover were tested in the majority of the experiments. Also tested were different plant and row spacings as well as planting systems. Manual and mechanical covering were applied in different experiments. The onion shoulder color was measured with a tristimulus colorimeter. The color characterization was done with the Hunter Lab scale. Several whiteness indexes were calculated. Early covering, four to six weeks before harvest, clearly reduced shoulder greening and increased whiteness in all the white onion varieties tested. Covering did not have a detrimental effect on yield. Mechanical cover was satisfactorily performed with three-spider rolling cultivators. Early covering did not have an effect on the incidence of rots. Direct seeded onions on two rows, 25 cm apart on 1 m beds, in the bottom of a furrow constructed on top of bed, appeared as a promising system for the Rio Grande Valley Area. Transplanted onions on two rows, 10 to 15 cm apart on 1 m wide beds resulted satisfactory for the High Plains Area.