then it goes on to `` anti-crop bw agents '' , which they say would be used as economic weapons , as i personally think is the case with the blofeld scheme , and they mention a whole list including potato blight , cereal stem disease , crown rust of oats , curly top disease of sugar beets , block rot of crucifers and potato ring rot , and insects such as the colorado beetle and something called `` the giant african land-snail '' , which i somehow do n't think we need worry about .