Pink root (Phomaterrestris) is among the major limiting factors for the production of sweet onions on Maui, Hawaii. Few management options exist for the control of pink root in onions. Two split-plot experiments were conducted in the area of Kula, Maui, over 2 years to evaluate several alternative management practices. In Expt. 1, the main plots were a rotation with cabbage, solarization with a clear plastic mulch, and a fallow period. Subplots were plus or minus Vapam fumigation. Sub-subplots were biomass application of Sudex or rape, inoculation with an EM biostimulant, and control. Each treatment had four replications for a total of 96 plots. In the follow-up experiment, the main plots were Vapam fumigation, rotation with either a Sudex or rape cover crop, and controls. The subplots were plus or minus EM biostimulant application. In Expt. 1, three separate treatments: solarization, cabbage rotation, and Sudex incorporation had a synergistic effect with Vapam fumigation. Fumigation and solarization also decreased pink root incidence. Rape contributed to a decreased disease incidence while EM contributed to increased bulb size. In Expt. 2, EM and rape contributed to increased yields. Rape and sorghum rotations contributed to decreased pink root incidence. EM inoculation had differential effects on several diseases, contributing to reduced bacterial bulb rot levels. The data indicate that growers may have several alternative management tools at their disposal, in addition to proper varietal selection, to improve yields and reduce disease incidence in sweet onions.
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