Swedes rotting

Hi, my swedes have been growing well all year and have now started to rot in the centres. They give off a pungent smell and leak a nasty slime at the base of a leaf stem, some leaves drop off and smell as well.

They have been under attack from catterpillars which have stripped a lot of leaf tissue. I shall net them next year but I didn't know catterpillars ate swede. This has weakened the plants resisitance to attack so may have contributed to the problem.