Ruud Kleinpaste: Tomato blight

Always a bit of a bummer when you grow tomatoes: Blight is one of those diseases that can cause a lot of damage and quickly.
Two varieties: early blight (Alternaria solani) and late blight (Phytophthora infestans). This last species is a close relative of the famous potato disease that cause massive potato crop losses in Europe, especially Ireland, which led to the horticultural Refugee movement and the run to the New Americas.
First of all: “early” and “late” are not sound diagnostic names for the disorders, as both can be “late and “early” respectively.
Alternaria can be identified by its leaf-spotting, and associated rots on developing fruit, especially at the distal end (non-stalk end)
Phytophthora has characteristic lesions on the base of the plant – often on the lowest parts of the main stem, just above the soil. The stem looks black and often “narrower” in patches.
Later that develops into a more obvious symptom whereby the leaves start to droop, go yellow and often shrivel up. By then it might be too late to save the plant.
With both blight species it s best to prevent an infection before it gets that far:
1) Keep your plants pruned from the bottom leaves upward. Every time you take the laterals off, check if you can prune the bottom leaves off, so they are not in contact with the soil.
2) Prune those leaves on a dry day – and clean your secateurs regularly
3) Water the plants by depositing the water on the ground/soil, NOT on the leaves and especially avoid wetting the bottom leaves
4) Every now and then spray the leaves with a copper spray solution (Copper Oxychloride or liquid copper) or a regular fungicide (Fungus fighter – myclobutanil etc); the copper acts as a preventative barrier and the fungicides have some systemic action that can fight the infection from inside the plant tissue
5) Regularly feed the plants (liquid fertiliser – seafood soup/seaweed tea), which will give them resistance.
6) Don’t grow tomatoes in the same spot year after year – change position in your garden; in glass houses or tunnel houses change the soil mix every other year or so, creating a fresh growing soil from time to time
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