In longitudinal sections, one or more inner scales will look watery or cooked. The disease progresses from the top of the infected scale to the base, where it can then spread to other scales, rather than spreading crosswise from scale to scale. Eventually, all the internal tissue will rot. Finally, the internal scales dry out, and the bulb shrivels. Squeezing the base of an infected plant causes the rotten inner portion of the bulb to slide out through the neck, hence the name 'slippery skin'.
Severe disease can occur during periods of high rainfall combined with strong winds or hail.
Heavy irrigation and persistent dews are also conducive to this disease. This bacterium is soilborne, and can be readily water-splashed to the foliage and necks, where it can enter through wounds. As the plant matures, it increases in susceptibility, with the mature plant being highly susceptible. However, in storage, the decay moves slowly, often requiring 1 to 3 months for total decay. Onions should be harvested when the bulbs have reached full maturity, and should not be stored until they have been properly dried.