[Edi]

Addendum: I'm not sure which disease it is, resistable or non-resistable. The bless death weapon is 448, and the disease weapons are 143 (non-resistable) and 414 (resistable). I recently played a game with Helheim using a D9 bless and it did not seem that enemy units got diseased 100% of the time. Only around 75% to 95% of the time, depending on how good MR they had, so the bless death secondary is probably 414 and resistable.

Unfortunately it is not possible to display weapon data with shift-i the same way you can for units, so if there is more than one weapon with the same name and that name appears as a secondaryeffect, it becomes a guessing game. I do not always guess correctly and it looks like I have guessed incorrectly for the bless death in the past.