Worm in tomato stem

[KCinNC]

Noticed last week that one of my Momataro plants wasn't looking too good.
Well it looked a little worse today so I pulled it up. I suspected some sort of blight or wilt and wanted it away from my other plants.
When I pulled it I noticed a brown section of stem above the soil line and the stem was very weak there.
I broke the stem open and could see where a worm had been but didn't find the worm. I hope it doesn't find it's way to any of my other plants.
I hated to lose a plant loaded with tomatoes but I've got 51 more.
Has anyone else had this problem and what type of worm would this be?
I spray with eight maybe 3 or 4 times a season but use fungicide weekly. Not sure any type of spray would be very effective on something inside the stem.
Thanks for any info.