A UD fact sheet, updated in February of 2017 gives timely info on leaf spot diseases of garden tomatoes. Fungal leaf diseases such as Septoria, bacterial leaf spot, and early blight can cause loss of leaves. 
Some leaf diseases such as anthracnose can lead to problems on ripening fruit. Click link below for fact sheet:
Tomato-Leaf-Spots-Fact-Sheet-Feb2017
Tag: tomato
Weather Favorable for Late Blight in Tomato and Potato
May 31, 2018 - The weather on the Delmarva has been favorable for the development of late blight in potato and tomato. See the updates from Rutgers at: http://plant-pest-advisory.rutgers.edu/potato-tomato-disease-forecast-9-1-17-2-2-2-2-2-2-2-2-2/ or http://plant-pest-advisory.rutgers.edu/ipm-update-5-30-18-2-2/
Scout fields and submit any suspect samples to your local County Cooperative Extension Office.
May 31, 2018 NFG
Leaf Spot Diseases in Garden Tomatoes
Fact sheet, February 2017 on leaf spot diseases of garden tomatoes. Fungal leaf diseases such as Septoria can cause loss of leaves. 
Some leaf diseases such as anthracnose can lead to problems on ripening fruit. Click link below for fact sheet:
Tomato-Leaf-Spots-Fact-Sheet-Feb2017. 