Nibble(Plant gets -1/-1) and Evaporate (Kill a dmged plant) dont work together.

[NoEscape1191]

When you use Nibble on a plant you can see that their stats turn red (which indicate that they are hurt), so why cant I use Evaporate on said plant? I thought that would work but it didnt and it actually costed me a game. 

[UnSurreal]

I'm guessing reducing it's stats does not equal damaging a plant. Which makes sense why it wouldn't work.