I cant seem to find the answer I need to identify and treat the spots on my cucumber plant. Ive read that it may be a magnesium deficiency, bacterial or possibly an insect. Help me figure this out so i dont lose the crop.

Unfortunately cucumbers can be very disease prone. Hopefully you can get a decent crop before things get too bad.

Could be a fungal problem. If so, you don't want to do any overhead watering; soak the soil without getting the leaves wet. You could try an organic fungicide, and there are recipes online for mildew sprays using milk. Don't remember the recipe, but I tried one out on a rose bush once and it did seem to help.