"Grooves about 1/8" wide" -- are they dark colored, random, kind of twisting tunnels -- if so, this is the sign of root maggots, which are a common pest on many root crops, especially those in the cabbage family, which includes radishes, turnips, rutabagas.

There are various pesticides you can use in the soil to deter them. Or, you can cover the patch tightly with floating row cover to keep out the adult flies.

The tunnels are random and twisting. I have problems growing radishes also.

I will try the row covers.

Thanks.

Do I need to be concerned about overheating under the row covers if the ambient temperature gets over 80 degrees Fahrenheit?

Here in zone 6 I use row covers on a huge range of crops. No problems with overheating.

Thank you.

As was said, likely it's root maggot.

That said, it's critical to understand that the row cover won't work if the plants are grown in the same area next season.

The reason: Part of the fly's life cycle is in the soil, adjacent to the roots. Row cover will used in previous site will provide an excellent protective environment for the pest.

The guideline: Plant in a new area, and use row cover.