A tomato plant is prone to several types of disease that can see your tomato crop ruined.
Early blight is a common tomato plant disease that starts with dark rings on the leaves and spreads. The leaves die and without their protection the fruit burns up. It can be treated with a sulphur or copper spray.
Late blight can quickly destroy the tomato plant and fruit. It’s a fungus that looks like spots full of grease on the leaves that spread to the fruit. A copper spray won’t work as a cure but should be used as a deterrent.
Verticillium wilt is prominent in cool weather. It affects the ability of the plant to take in water. It becomes apparent as the leaves appear to wilt during the day only to recover at night. Eventually the plant will die. The only cure is to remove and discard the plants. Don’t put them in the compost.
Grey Leaf Spot
Grey leafy spot will affect the leaf but not the fruit of a tomato plant. The leaves will turn yellow and die. All you can do discard the affected plants. Don’t compost them.
Septoria Leaf Spot
Sometimes mistaken for late blight, septoria leaf spot can be treated. Patches occur on the leaves with dark speckles in them. Using a copper spray can cure this disease.