Is there a difference between 杀害 and 杀死? I have tried browsing examples, but the only potential difference I see is that you can say "它也会杀死庄稼", but I am not sure if 杀害 also refers to plants.
害 in 杀害 (kill; murder) means 'victimize'. You can only victimize creatures that have emotion, capable of feeling pain. '杀害' mostly refer to murder of human; And only killing of human can be deemed 'murder' 

Note: only human intentionally killing other human is called 'murder' . A tiger killing a human is not a murder, but a killing 

杀死 (kill someone/ something dead) can apply to any living organism, from single cell bacteria to human