Answer: These plants are usually pest and disease free so there is no common culprit to suspect. I would not expect a fungal infection to cause holes (or to bother coleus.) You might look carefully for snails or slugs, slugs are nocturnal and leave a shiny trail behind. They can be controlled by hand picking or by using a bait with iron phosphate as the active ingredient. IF there are large portions of the plant missing, you might have a woodchuck or deer or other animal bothering your plant. These can sometimes be deterred by using a repellent (sold at garden centers.)
If these are the newer sun coleus, they should be alright in afternoon sun as long as the soil is evenly moist like a wrung out sponge, not sopping wet and not dried out. If however they are the old fashioned coleus, they would do better in morning only sun or bright dappled light all day. If you are not sure which kind you have, perhaps you can check with your retailer.
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