Bombs are blockers in Farm Heroes Saga. They are like the normal cropsies but have a countdown number on them. Once this number has reached zero they will explode and destroy part of your harvest. To prevent this you will have to do a match or throw a water drop at them. Bomb Cropsies do not score. Neither will they be added any bonuses. At the end of a level they may be harmless if their count is higher than the number of remaining moves. Hero Mode will convert the bomb cropsies into normal ones which makes bomb levels often a close call.
Igniter Companions will ignite one bomb each time. Unfortunately it can be one with a high count. Water Drops or Shovel Hits are another remedy. Frogs make no difference between bombs and regular cropsies.