Tomato stems turning black

Edit: Additional picture in the comments

My newer tomato shoots are turning black and I'm urgently trying to figure out why. All the plant sites are unanimously convinced that it's late blight, stem canker or a related fungal issue, but the plant simply doesn't display symptoms for these diseases- there are no lesions or sores, only a gradual darkening on shoots that is mostly uniform. If I look very closely, I can see many individual (very small) black dots. Any ideas? Thanks in advance!!