Does anyone know what causes this?
Does anyone know what causes this?
A friend had similar damage on some bulbs last year and determined the cause was amaryllis borer, aka lily borer. Photos here: https://en.wikipedia.org/wiki/Brithys_crini
She had also planted the bulbs fairly deeply last year. This year, she kept the shoulders well above the surface and didn't have this issue... coincidence, perhaps? or the more mature borers like to operate underground if they have the chance.
I'd cut off that damaged leaf and cut out any black/soft/rotted areas... go deep if you have to. Dust the cut areas with cinnamon (or dunk in fungicide), let it dry a week or two, then pot up. If you had to cut deeply, you may not get bloom this year, but amaryllises are pretty tough and usually rebound. Be careful not to overwater a damaged bulb and watch out for rot (soft, slimy, or black areas... it'll smell funky, too).
Cinnamon? That's interesting. Thanks for the info.
Cinnamon is a natural anti-fungal, anti-rot agent... better smelling than dishwasher detergent powder, too, although I think the "iris people" mostly swear by using Cascade on soft rot (after cutting away the soft part).