Hi all!

We grow tomatoes for our small family farm here in Phoenix Arizona. Been at it for many year but have a disease that always ends up causing us much grief. We grow our tomatoes from seed and transplant into our high tunnel in early February. Grow them on string line and by May we are getting huge harvests. But its usually about that time that our disease shows up. Always starts from the bottom up as you can see in the photos and video. Bottom leaves die and the stem starts to brown. Tops will be fine even the bottom looks awful, but it keeps climbing until it consumed the whole plant. Culturally wwe have grown these both in the ground and now in grow bags with a drain to waste hydroponic system. Honestly we went to the hydro system because we believed that the disease was soil borne.....but it showed up even still. Other considerations: No overhead watering (to keep disease down). Phoenix's weather is cool until late April then heats up rapidly. By late May we apply shade cloth to the high tunnel as we see temps above 100 solidly after that. Most plants expire by July 4th due to extreme heat, and thats fine. We have had plenty of harvest usually by then. The issue is that this disease is taking plants down in April. We did wonder if it was a heat related issue, to test it we planted a fall cool weather crop this year. Unfortunately we are seeing the same disease paterns even in cool weather.
So tomato experts! Whats your thoughts>
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Not a disease expert, I'm hoping some of the greenhouse growers will get in here to help you. I am guessing it is grey mold, which can thrive in the high humidity of some tunnel and greenhouse environments.

I'd send the description along with these photos to your extension folks.

This could be the same or similar to the blight we get here when it's hot (by local standards) and humid. But ours starts in the upper canopy, resistant leaves get purple splotches but take a long time to produce spores on the underside. There are some crispy leaf ends but the stems and leaf axils can hold out a long time. Susceptible plants rapidly get it on the new growth in the axil and also their stems. Kind of a pale brown color. I've been thinking that it is a type of Alternaria. I dip my pruners in bleach to stop the cut ends from getting infected. That works, but the stuff keeps coming until temperature and humidity drops.

I wonder if the starting at the bottom is because it is seedborne? Are you saving and using your own seeds? That might explain why it returned after the change to hydroponics.

I get what looks like the same thing no matter what soil it's in..
Not saved seeds.
Sometimes it grows out of it if I keep trimming and diligence prevails.
Sometimes not..
This is the main reason I quit growing tomatoes and instead grow peppers.