This article from HDRA I have posted here before. It is dated 1999'
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POTATO & TOMATO BLIGHT
Article from HDRA Summer 1999 (Issue 156)

Caused by fungus Phytophthora infestans; thrives best in warm & damp.

SYMPTOMS
Potatoes
Dark brown or blackish, round patches on leaves and later on stems.
The underside of theses patches develops a downy white coating of
spores. May spread rapidly.
Tubers develop dark, sunken areas which may cover whole tuber in a
dry, firm rot. Other fungi and bacteria may invade producing a foul
smelling soft rot. Tubers may develop this while in store.

TOMATOES
Foliage symptoms similar. Fruits develop brown leathery patches which
may appear several days after picking.

LIFE CYCLE
Disease suvives the winter in infected potato tubers in the soil or on
compost heaps. The foliage which grows from these develops spores
which spread on the wind. Can come from many miles away.
Spores develop at temps of 10 degrees C with humidity of 75% for 2
days or more.

NEW STRAINS
Until the 1970s there was only one type of blight in UK which was
unable to produce spores which could overwinter. Now there are 2
types which can mate and produce resistant spores.

PREVENTION & CONTROL
A HEALTHY START
Plant good quality seed from a reliable source.
Most Early vars are very prone. Plant and harvest early.
Good maincrops are Cara, Stirling, Teena, Torridon, Remarka and
Romano.
No blight resistant tomatoes as such.

GOOD HYGIENE
Remove potential sources of infection, especially ALL tubers.
Burn, dustbin, or bury at least 2 ft deep.
Same for tomato fruits.
A good active compost heap will deal with potato and tomato haulms.
Increase ventilation; space widely to avoid too much humidity among
plants.
Greenhouses should be well ventilated and waterproof. Water from
below.

IF BLIGHT STRIKES
In warm damp conditions remove all blighted leaves, even all foliage
to prevent spread to the tubers. Don't harvest the crop for at least
3 weeks to allow thicker skins to develop and soil-surface spores to
die.

Check stored tubers regularly.




Pam in Bristol