So sorry, it looks like you may have root maggots tunneling into your turnips. This insect starts as a small fly that lands on the turnip green when young. Then it lays eggs that hatch larvae or maggots that burrow into the roots. Many cruciferous crops are attacked by these flies. The best control is to prevent the fly from landing on the crop so that no eggs can be left. In the spring cover the turnips with floating row covers or spun polyester just as the green leaves appear. Good luck and Keep Growing, Marianne Binetti