Yes Mr. Khan, I am inclined to agree with you.
The amount of biological matter required to cause total chaos amongst allied troops could be contained in a 1litre water bottle and hidden just as easily. A few artillery round deliberatley wrongly marked as HE would probably pass inspection unless closely examined, which the troops don't have time for. One oil drum or jerry can amongst a hundred others probably wouldn't be spotted either.
The idea that any WMD are going to stand out for all to see is erroneous in the extreme. A more fragmented and highly camouflaged operation would probably be hard to find, (pun not intended!).