Does this homebrew way of delivering poisons have unforeseen consequences?

I am running a homebrew tier 3 adventure in which the players will eventually encounter vampires. I’d like to introduce an item that will be particularly effective against vampires and vampire spawn, without it being obvious that this is the case. In addition, I’m dissatisfied with the efficiency of poisons. Basic poison, in particular, seems very weak for its cost. More expensive poisons don’t seem to scale well either.

I drafted a magic weapon that I believe handles both these problems. The intent is that this weapon appears to be a way to make certain consumables more effective, but in reality is intended to be of superior use against vampires in particular, due to its ability to deliver holy water.

Here is what I drafted:

Infused Yew Dagger

Weapon (dagger), Uncommon

This wooden blade is porous and stained multiple faded colors. You can apply to the blade any fluid which can be spread on a weapon (such as Poison) or flung (such as Oil,) infusing the blade with that substance.

For 1 hour after application, the blade gains the following property:

The first time you hit a creature with the blade each turn, the effect of the most recently infused substance is applied to the creature in addition to the normal piercing damage (that creature can make any relevant saving throws allowed by the infused substance.) If the substance would normally lose its potency after its effect is applied, it does not.

Whenever the blade is unprotected and takes any amount of acid or fire damage, it is rendered useless.

The specific question that I want to be answered is: Does this weapon do anything overly powerful beyond what I intend it to?

For the purpose of this question, we can ignore whether the rarity is correct, as well as whether or not poisons are actually too weak.

My specific intent with this weapon is the following:

  • Since it is a dagger, it will not be the usual weapon of choice outside of its niche.
  • Since it is wooden, it can be used as a stake for vampire hunting.
  • It is a particularly effective way of delivering holy water.
  • It does not work more than once per turn, and should therefore not be too abusive given the typically short length of 5e’s combat.
  • It allows poisons to be used for longer than their restrictive one minute/one use clauses, while still allowing a save for the more powerful poisons.
  • The last clause does not support the less expensive acid option, which I believe would be too strong for the cost.
  • The last clause does not support alchemist’s fire, which I feel would be strange for a wooden weapon.

Does this weapon have other severe balance implications, or other abusable options that I have not considered?