Yes, under some conditions, though care must be taken to avoid reducing yield.

Higher nitrogen (N) application rates can lead to thicker necks that take longer to dry during field curing. When onion tops fall over, the senescing leaf and neck tissue loses resistance to bacterial and fungal pathogens. While the neck tissue is still green, there is adequate moisture in the necks for these pathogens to infect the tissue and move down the neck towards the bulb. The longer the leaves and neck of an onion plant take to dry down, the longer the window of susceptibility of the plants to infection by plant pathogenic bacteria and subsequent disease development. However, because of the indirect nature of how high available N affects this, and the many factors that affect onion plant response to N, research results on the effects of N application rates on bacterial bulb rot often are inconsistent. Some studies have demonstrated that bacterial bulb rot increases with increasing N application rates, and this increase continues at N rates above those needed to maximize marketable yield^1,2 . Other researchers have found no response of bacterial bulb rot to N application rates or that bacterial bulb rot was only reduced at N application rates that also reduced marketable yield^3,4.

Effects of N application rates on bacterial bulb rot are most likely observed under high bacterial disease pressure and when other conditions increase the risk of bacterial bulb rot (e.g., rains during field curing or excessive irrigation near maturation of the plants)⁵. Because of the impact of N application rates on bacterial bulb rot under these conditions, it is important to note that the N application rate required to maximize marketable yield is likely lower than the N application rate required to maximize total yield when conditions are favorable for bacterial diseases. Nevertheless, given the risk of yield loss if N application rates are decreased too much, and the numerous reasons to avoid over-applying N that are independent of the impact on bacterial bulb rot (input costs, nitrate leaching, etc.), it may be more challenging to reduce the risk of bacterial bulb rots by reducing N rates compared to modifying irrigation and other late-season cultural management strategies.

Citations:

¹ Díaz-Pérez, J. C., Purvis, A. C., and Paulk, J. T. 2003. Bolting, yield, and bulb decay of sweet onion as affected by nitrogen
fertilization. Journal of the American Society for Horticultural Science 128(1):144–149.
https://doi.org/10.21273/JASHS.128.1.0144
² Leach, A., Reiners, S., and Nault, B. 2020. Challenges in integrated pest management: A case study of onion thrips and bacterial bulb rot in onion. Crop Protection 133:105123.
³ Díaz-Pérez, J. C., Bautista, J., Gunawan, G., Bateman, A., and Riner, C. M. 2018. Sweet onion (Allium cepa L.) as
influenced by organic fertilization rate: 2. Bulb yield and quality before and after storage. HortScience 53(4):459–464.
https://doi.org/10.21273/HORTSCI12360-17
⁴ Gugino, B. K., and Mazzone, J. D. 2023. Evaluation of the effect of nitrogen rate and timing on the incidence of bacterial
disease of onion, 2021. Plant Disease Management Reports 17:V147.
⁵ Wright, P. J. 1993. Effects of nitrogen fertilizer, plant maturity at lifting, and water during field-curing on the incidence of
bacterial soft rot of onions in store. New Zealand Journal of Crop and Horticultural Science 21(4):377–381.