Ustilago maydis overwinters as the teliospores produced in the galls. The teliospores do not infect other corn plants, and there is no plant-to-plant spread during the season. Teliospores can survive in the soil and on infested plant debris for many years. The spores can be spread by wind, splashing rain, and the movement of soil and crop debris, but they will not result in infection until the following season(s).
 

Under favorable conditions, the teliospores germinate and produce a second kind of spore called a sporidium (sporidia, plural).^1,3,4 These sporidia also cannot infect corn plants on their own. When a sporidium germinates, it produces a germination tube that can fuse with a germination tube of a sporidium of a different mating type. (Mating types of Ustilago maydis are complicated, and we won’t go into that here.) The fusion of the two sporidial germ-tubes forms an infective hypha (fungal thread) that can infect the corn plant. For ear galls, this infective hypha grows down the silk channel and infects an individual, unfertilized kernel. Infection of other tissues is often most severe after wounding by blowing soil, hail, or other factors.^1,4
 

Once they penetrate the plant, the fungal hyphae grow between the corn plant cells, absorbing nutrients, but the cells remain alive and intact. The hyphae cause the cells to grow abnormally, dividing and enlarging to initiate the growth of the gall.
 

Gradually, the hyphae grow and replace the plant cells in the gall. Eventually, the fungal hyphae transform into the teliospores that fill the gall.^1,4 The conditions that favor smut development have not been well defined or documented. Some reports indicate that infection is more likely after periods of humid, rainy weather, while other reports say that the disease is more severe after dry periods.^1,3,4 Thunderstorms and strong winds that blow soil can injure plants, resulting in sites of infection for the smut pathogen. Injury resulting from detasseling can also result in increased numbers of infections.
 

There is also some evidence that high levels of nitrogen fertilizer may result in vigorous growth of corn plants that may increase the chances of smut infection.⁴ Because ear galls result from the infective hyphae growing down the silk channel to infect unfertilized kernels, any factors that delay fertilization and prolong the presence of green silks can increase the likelihood of developing ear galls. Hot, dry conditions that result in reduced pollen production or asynchronous production of pollen and green silks can prolong the time that kernels are susceptible to infection. Once a kernel is fertilized, a barrier forms between the silk and the kernel, the silk dies, and infection can no longer occur.^1,4
 

Teliospores are released when galls break open during the harvest of seed crops of sweet corn, and these teliospores may contaminate the harvested seed. However, teliospores do not infect the seed and are not able to cause post-harvest disease. Generally, common smut of corn is not considered seed-transmissible.⁴

The primary method used to manage common smut in sweet corn is the use of smut-resistant varieties. While there are no sweet corn varieties with complete resistance to common smut, varieties do differ in their level of susceptibility. Smut resistance in corn (field, sweet, and pop) has been studied for almost 100 years, and partial resistance has been found in some inbred lines. However, the genetics of smut resistance are still not well understood, and major resistance genes have not been identified.^1,3,4
 

Some disease and pest management guidelines recommend practices such as crop rotation, seed treatment or foliar fungicide applications, and fertility modifications (avoiding high nitrogen levels). Because of the biology of this pathogen, these methods generally have not been effective for managing common smut on sweet corn in areas where corn smut is established.¹