Concept is a great take on the theme and a unique game idea.. Win condition appeared to be bugged for me, unless I simply failed to understand it. When I destroyed enough trees to deplete the anti parasite's health bar, it showed the anti parasite victory text. The only way I was able to win was to go directly for the anti parasite flower and consume it, which seems to be the easiest/quickest route to victory. Camera movement was a bit wonky, and sometimes horizontal movement seemed to get stuck. AI is indeed pretty inept. It would've given the game some more replay value to introduce difficulty levels, where each difficulty increases the speed at which the anti parasite plant expands.
Great work, and congrats on completing the game!