Complex sentence: Radishes can be useful as companion plants for many other crops, probably because their pungent odour deters such insect pests as aphids, cucumber beetles, tomato hornworms, squash bugs, and ants.
Split into simpler sentences: Radishes can be useful as companion plants for many other crops. This is probably because their pungent odour deters such insect pests as aphids, cucumber beetles, tomato hornworms, squash bugs and ants.