The festival of the Robigalia is celebrated to appease the God Robigus (or perhaps the Goddess Robigo; the gender of this deity, who originated as one of the numinae, is uncertain), who is the deity of wheat-rust, mildew, and blight.
It is an ancient festival of the agricultural calendar, and is celebrated by the Flamen Quirinalis. Both a red dog and sheep are sacrificed to Robigus, along with wine and incense; prayers are then spoken to protect the crops. There is some connection with the ascension of the star Sirius, but it is unclear.
Games (ludi) in the form of “major and minor” races were held. The Robigalia was one of several agricultural festivals in April to celebrate and vitalize the growing season, but the darker sacrificial elements of these occasions are also fraught with anxiety about crop failure and the dependence on divine favor to avert it.
Verminus, a God who protects cattle against worm disease, might also be honored on this day.
The Robigalia has been connected to the Christian feast of Rogation, which was concerned with purifying and blessing the parish and fields and which took the place of the Robigalia on April 25 of the Christian calendar.