A medieval term for the interference with the fertility of crops, humans, and animals, by witches. If a farmer suffered a poor harvest, he might well blame it on a witch for "blasting" his crops. If a woman miscarried, she might claim she had been blasted. It was said that the spell for blasting included the flaying of a cat, lizard, snake, or toad, then reducing the skin to ashes over a fire made of yew, hawthorn, and elder. The ashes were scattered over the farmer's fields or sprinkled on the threshold of his house.
In fact, true Witches are very pro-life and work for fertility, not against it. But this was part of the propaganda of the early Church, a reversal of true pagan ways to make them appear negative. In the Malleus Malleficarum (1486), the second of its three parts deals with a number of sexual matters (with which the inquisitors seemed especially fascinated), including the methods used by witches to dull the powers of generation and obstruct the sex act. It also deals with how they cause the male organ to disappear, how they kill a child in the womb, and how they injure cattle and raise storms.
The two monks who wrote the Malleus Malleficarum were quite specific when it came to descriptions of these acts: "Intrinsically they cause (obstruction of the procreant function) in two ways. First, when they directly prevent the erection of the member which is accommodated to fructification. And this need not seem impossible, when it is considered that they are able to vitiate the natural use of any member. Secondly, when they prevent the flow of the vital essences to the members in which resides the motive force, closing up the seminal ducts so that it does not reach the generative vessels, or so that it cannot be ejaculated, or is fruitlessly spilled."
But blasting could also be done with the evil eye, by the witch just looking at the person or thing and muttering a curse. Charges of blasting were frequently made against witches and, as with so many false charges, were almost impossible to disprove.