Brussels sprouts that develop hollow stems is caused by either a severe boron deficiency in the soil OR excessive nitrogen and a rapid rate of growth while still very young. That leaves the plant susceptible to any number of soil-borne fungus and bacterial diseases.

IMO your plant is displaying some of the classic symptoms of Yellows (Fusarium Wilt) and there are also other potential fungus issues at work. At this point of advanced disease the plants cannot be salvaged. Sorry.

Dave

Thanks Dave.

I pulled them today and split apart the stems. A couple of observations.

1) Black specks inside the stems. Maybe frass? My son found a couple of cabbage worms on the seedlings a few days after we got them from the nursery.

2) Molted skin - Brown black inside the stem

Overall, they went quickly, so I think (and use that lightly based on my amateur status ) that there was a pest that helped a fungal issue take hold.

This was my third time in 5 years trying to grow Brussel Sprouts. One year the soil wasn't right, One year the soil was good but I planted out too soon and we had a blazing hot summer (bitter plants with loose heads), now this year. :-(

Thanks for your input!