Altering Planting Configurations to Manage Bacterial Bulb Decay in Large-Scale Onion Production
Bacterial diseases of onions have become a serious threat to the sustainability of the New York onion industry. Losses up to 40% can occur as a result of reduced onion quantity and quality. Ultimately, an Integrated Pest Management (IPM) approach will be required to manage bacterial diseases of which cultural practices will be important components. Recently, studies with small-scale production of onions on plastic mulch showed that when plant spacing was reduced from 6 or 8 to 4, this provided 53 to 64% control of bacterial bulb decay at harvest. Marketable yield also increased by 1.4 to 2.4 times due to more marketable jumbo-sized bulbs. Wide plant spacing produced big bushy plants with more leaves, thicker necks, delayed maturity and bigger bulbs, and it was these bigger colossal-sized bulbs that rotted. By narrowing plant spacing, having significantly more healthy jumbo bulbs more than made up for fewer colossal bulbs. Whether reduced plant spacing also reduces bacterial bulb decay in direct seeded onions that are already grown at high plant populations warranted investigation. The purpose of this project was to evaluate the effect on bacterial bulb decay and yield of plant and row spacing, and bulb area in large-scale production of direct seeded and transplanted onions. An on-farm small-plot research trial was conducted using transplanted onions (c.v. Canady) and included 13 planting configurations. Plant size and maturity trends were generally opposite of what was found previously in studies with small-scale onion production: in this study, plant height, number of leaves per plant and maturity generally increased as plant population increased. Despite this, yield and bulb size distribution were similar to previous results. There was a general trend that total yield, boiler, small and medium sized bulb weight, and economic return increased as plant population increased. Within each row spacing (15, 10 and 7.5), these parameters increased as the plant spacing decreased from 8 to 6 to 4. Although less dramatic, within each plant spacing (4, 6 and 8), these parameters increased as row spacing decreased from 15 to 10 to 7.5. Generally, yield increased as plant population increased because there were more bulbs per area to contribute to yield. Our data suggests that plant spacing is a stronger predictor of yield and bulb size than row spacing or bulb area. Bacterial bulb decay 9 weeks after the onions were pulled from the field ranged from 0.8 to 3.6% incidence and no significant differences occurred among planting configurations. There were no significant correlations between incidence of bacterial bulb decay and plant size, maturity, yield and bulb size distribution. There was no relationship between bacterial bulb decay and plant population. Repeating this study is certainly warranted in order to generate robust data from which to make recommendations for planting configurations to manage bacterial diseases in large-scale onion production.
New York State IPM Program
Agricultural IPM; Onions; Vegetables