Lilies

Question

What causes the leaves to get holes or splits in them?

Answer 1

This could be a Lily Beetle, or hundreds of other type of insects could cause the issues.
A Lily Beetle is bright red and should be able to be seen on the plant.

I would treat the plants with Neem Oil. Neem Oil is organic and is safe for people, pets and bees.

https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm