Hard to say with the info given. My guess, with only the info given, is fireblight. But that's just a guess. Pics always help a diagnosis. Dan

Looks like the beginning a scab, a common fungal ailment of various apples, crabapples and pears. You can spray for control but if annual problems, suggest you replace with a disease resistant variety.

There are all sorts of causes to bark splitting, usually a response to an environmental factor like frost/thaw, sun scald, even fluctuating weather/temperature conditions. Fruit trees - like the crab - have thin bark and are quite prone to splitting. Typically it is more of a cosmetic issue than a serious threat to the health of the tree and the tree is usually able to adapt to and seal/scar over the split with ease. Here is a link that might be useful: the 411 on bark splitting

Why a weak dose of fertilizer? Because I read on this forum about the "weekly weakly" thing. I had also already fertlized with Jobe's Organic but it is the kind you just sprinkle around the base of the tree and water in, I was afraid the tree might need something a bit more direct until that had a chance to soak in. The fertilizer i just used is 8-7-6. What formula? The fertilizer i just used is 8-7-6. When did you last fertilize? Yesterday How often do you fertilize? Haven't been since I got the tree a few months ago, just started with the Jobe's about three weeks ago, then the 8-7-6 liquid yesterday. What kind of soil is it in? gritty mix How much light does it receive? in a sunroom with S/SE exposure Could the aphids be causing this? I've been spraying with neem.