Could it be pigeon damage?
Ive grown swiss chard for three years & never had to cover it or protect it at all. It has been pretty indestructible but for some reason this year the pigeons have been attacking it :o
I actually saw them doing it & had to chase them away. Ive got no idea why they are suddenly interested in it except maybe its because I am getting much better at covering/protecting my brassicas, fuits etc & the chard was the only unprotected item on my plot at the time
