Tomato disease identification is quite difficult, if you want or need to know exactly which disease is affecting your tomato plants. However, as a large number of tomato diseases have similar indicators and many of them have no cure, recognising that there is a disease present is probably more important than knowing exactly what it is. This is because diseased plants and fallen leaves from those plants need to be gathered up and destroyed as soon as possible before they infect the rest of your tomato plants or indeed, other plants in your garden.

If you're growing tomatoes and the leaves, stems and fruits look normal and blemish free and everything is growing at the rate and to the timescale that you expect, then your tomatoes are probably completely free of disease. However, if your tomato plants display any of the following symptoms, there is probably something wrong:

1. Leaves develop spots on either side
2. Leaves turn yellow
3. Leaves wilt
4. Leaves wither and die
5. Spots on leaves increase in size
6. Strangely shaped blemishes appear on leaves
7. Black or brown patches appear on stems
8. Cankers appear on stems
9. Mould grows on stems
10. Spots appear on stems
11. Tomatoes have dark brown blemishes at flower end
12. Tomatoes drop off plant before ripening
13. Tomatoes have discoloured patches
14. Sticky patches with small white flecks appear on leaves.

If you spot any of these signs, there's every chance that your tomato plants have some sort of disease so don't forget to destroy the offending plant immediately as well as any debris on the ground around it.