I'm not an apple expert, but if you could post some pictures it would help those that are more knowledgeable than I am.

Jason, I will try to get some pics on Sunday. Unfortunately, I won't be in until dark each night for a few days.

Basically, I just need advice on how to help apple trees--specifically columnar--to thrive.

Use myclobutanil (spectracide Immunox) for Cedar apple rust prevention. BIG thing is prevention not control. You need to apply before you get the disease.

This will also prevent apple scab too if that is part of the problem. Captan 50 WP is also a good fungicide to prevent apple scab. Available online.

Growing columnar,standard, dwarf or espalier apples should not make a difference as far as disease control. Granted, some apple varieties are more prone to scab than others but the prevention (use a fungicide) will apply to all.

Without pictures unable to tell what exact problems your apples are having. Unsprayed apples in my area get scab, cedar-apple rust (if junipers nearby), fireblight, sooty blotch ect. Very hard to get good fruit without spraying to prevent fungal issues. Or you could bag the fruits (paper, plastic, cloth bags) to grow them organically.