Shirley tomato problem

I had always grown Shirley tomatoes very successfully in a tunnel but last year my sister grew Moneymaker tomatoes and they developed a disease whereby shoots became mouldy and died back. This year the shirley tomatoes had it as well and a lot of the shoots died back early. i don’t know what tis disease s. I had assumed that shirley tomatoes were disease resistant. How do I clean up the tunnel to get rid of this disease?