Soapy water will kill the pests but you have to hit them to do it. It works on contact only.

In Pesticides class, the rule of thumb was holes "in" the leaves as fungus and bacteria which grow in water droplets.

And holes at the edges of leaves as insect or larvae, since that's a common starting point for a meal.

It wasn't an absolute, but it was a good guideline.

Thanks poochella. I have found a few slugs on my plants. I pick them up and discard them. I don't see many though. Can a few slugs do alot of damage?

How big are the holes, what shape, and where are they?

The holes seem to be on the inside of the leaves. Not very large. Some holes can be up to 1/2 inch. I have found a few slugs in my Garden. I have looked to see if their are critters inside the roled leaves and I don't see any.

Some of the shot hole fungus, etc., exude chemicals that burn foliage and the circular oval hole will be relatively smooth edged, possibly with a halo of grey or discoloration. Insects are not consistent with smooth even edged holes.