Try to find out from the Allotment secretary what* was applied and when. Perhaps ask to see the container, which will give information regarding replanting. Do all the plants appear to be dead?.
Hopefully, the treatment done was to allow use of the plot this year.I would be inclined to plant up ,depending on the replies you receive, as if all was good.You will soon see if things survive!
Perhaps proceed, working towards no dig from the coming Autumn, snatching a crop this year if you can.
*Feel free to ask further, from here or the manufacturers website once you know what was used.
Good Luck
Cleansweep
