- Tomato Disease Identification Key By Affected Plant Part: Stem and Whole Plant Symptoms (Cornell University)

- Tomato Diseases & Disorders (Clemson University)

- Vegetable Diseases - Five Steps for Healthy Garden Tomatoes (Purdue University)

- Backyard Tomato Disease (Alabama Cooperative Extension System)

- Tomato Diseases are a Gardener's Nightmare (Grow It Organically)

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TAMU - Texas A&M Tomato Problem Solver

Key to Tomato Diseases

UC IPM - Tomato Pests and Diseases

Planet Natural - Tomato Pests and Diseases

Tomato Nutrient Deficiency Symptoms

Rutgers Univ - Diagnosing and Controlling Fungal Diseases of Tomato in the Home Garden

Root Simple - how-to-diagnose-a-tomato-disease/

Solorado State - How to Recognize Tomato Problems

Missouri Botanical Garden - Tomato Plant Diseases

How to Identify, Treat, and Prevent Tomato Diseases

MSU - Greenhouse Tomato Problems

We have composed many lists in the past that are likely still here but many of the links on those old lists may have changed so it is a good idea to make up a new one. Keep in mind that almost every single state extension service also provides info on diseases local to your area.

USDA State Agricultural Extension Services Directory

Dave

Here's the University of Tennessee Institute of Agriculture Extension page with "tomato" as the search results. If you want something more specific, just add disease, or another term to the search field...

UT Ext. Search Results for "tomato"

Tomato Diseases [ thank you seranata ]

Tomato Diseases are a Gardener's Nightmare