It might just throw the dagger at the plant, though.
My biggest criticism about the VGA version is that the dagger's a bit finicky about what you'll do with it - and unfortunately it's a bit of a necessary evil. Sometimes, you click on something, and it'll throw it. Sometimes, like when fighting the kobold, you'll initiate combat.
In the EGA version, the thief can kill the kobold by throwing daggers at him, but that seems to be impossible in the VGA version (unless you can click past him and hit him that way?)
On the other hand, if the dagger was thrown instead of initiating combat, the Magic User would be SOL because once the Kobold gets Reversal active, the only way to kill him is to go into combat with Zap... which is... actually a lot harder in the VGA version than the EGA version for some reason - I ended up with a zombie Hero trying to do it in the VGA version.