Humans have a long and (in retrospect) not entirely proud history of eradicating bigger, badder, faster and hungrier predators, and there are a huge range of techniques that can be used.
The simplest thing that springs to mind is bait and poison. You'll need quite a lot of poison to kill something that big, but with a bit of practical research it can certainly be achieved. Perhaps you could feed Bessie the cow or Flossie the sheep a really substantial meal of water hemlock, monkshood, foxglove, nightshade and whatever else your local environment can provide. Dragons hunting for themselves will consume the bait and not fly far, or for long. Dragons hunting to feed their family will quickly wipe out their current brood.
Dragons feeding their family have to eat too, especially if they have to spend a lot of energy on flying around. Either both parents of a brood will poison themselves, or one will and the other will have to leave the nest to feed themselevs and their young, and some enterprising climbers can go up and either dispatch any surviving live young or steal or break the eggs as they see fit.
Electrical shock traps would be somewhat anachronistic, but the actual manufacture of an electrical motor (or generator) or capacitor isn't necessarily that difficult. The scope of these anachronisms is of course yours to handwave in. If you wanted "real" 14th century technology though, you're probably out of luck.
Also, having come fresh from a gunpowder weaponry question, and seeing your mention of rice, have you considered the benefits of gunpowder? Rockets and bombs and cannons firing clouds of shot would all have been achievable. Even if big shotguns aren't your thing, then the prospect of a sheep-bomb exploding in mid-air whilst held in the mouth of a big dragon should surely interest you. Much more technologically plausible than electrical mechanisms.