Late Spring and Summer is the time to be vigilant.  Trim bottom leaves from plants to improve air circulation.  This will help prevent the growth of fungus (both small leaf spots and late blight which is a larger spot on the leaf).  Be sure to also mulch to keep down weeds and keep air flowing under plant.  This is also a good time to fertilize.  Look for a good quality fertilizer such as Espoma 3-4-4 (NPK) 

Most bagged fertilizers for homeowners are labeled with 3 numbers. These are the BIG 3 or NPK (nitrogen, phosphorous and potassium) Nitrogen is most important and helps build protein in the plant, phosphorous aids in storing energy (photosynthesis) and potassium builds disease resistance.

The cause of the cracking is too much water.  This can happen by too much rain or over watering.  Either way, the plant has absorbed too much water and it is being absorbed by the fruit.  There is not much you can do except if you are over watering, cut back and that should help.

100% with original receipt 0 to 6 months for date of purchase.  50% 7 to 12 months for purchase.  Don't pull plants and assume they are dead.

Spring and Fall when all danger of frost is past.

No plants are deer proof, only deer resistant.  And when hungry enough deer will eat anything!