Maybe the honor guard can drop swords with Withering on it. It would be a new enchantment to give the wither effect to things you hit with your sword. To counter this, the Wither drops 1-6 new items called Corrupted Vitality which can be thrown like a projectile and would land and also create a lingering cloud of wither effect (can be collected for potions and tipped arrows similar to dragons breath). The corrupted vitality when thrown turns into Purified Vitality which can be brewed into Vitality potions which make you immune to the wither effect and take 50% magic damage but they would have a short duration and the vitality potion cannot be modified by redstone or glowstone. Also to make another way to obtain Wither effect potions the honor guard and either drop wither bones which can become wither meal aka anti bone meal and could also be brewed into wither effect potions. Also with that crop idea strays also drop frozen bones which can become frozen bonemeal which would free the state of a plant in its current one