Agriculture Reference
In-Depth Information
Blight
The worst problem for all potato and tomato growers in the UK is blight. This is
the same wind-borne fungal disease that caused the Irish potato famine, and
there is no cure. Whenever the outside weather turns warm and wet for a few
consecutive days any time from early July, the spores won't be far behind. These
periods of blight-favouring weather are known as 'Smith Periods', and you can
register online to receive blight warnings for your area (see the Potato Council,
Resources section).
If blight gets into the outdoor part of your plot, deal with it promptly by burning
all affected foliage. Do not go anywhere near your tunnel after dealing with
infected plants, as the spores will be on your hands, shoes, clothing and hair.
Shower immediately, launder your clothes and rinse your shoes with soap and
water or a 10-per-cent bleach solution. Then spray any tomato or potato plants in
the polytunnel with a bicarbonate of soda solution (see Chapter 7, page 58) to
reduce the chance of infection taking hold.
Bordeaux mixture (a traditional copper-based remedy) also has some effect in
the early stages of blight, but although commercial organic growers are allowed
to use it as a treatment of last resort, many gardeners are not happy to do so
because it is moderately poisonous in general but especially so for bees and
worms. Remember also that, once introduced into the enclosed space of a tunnel,
potential poisons such as copper are difficult if not impossible to remove.
If the disease does get into the tunnel, all you can do is remove any affected
growth and burn it, and continue spraying with bicarbonate every few days to
slow down the spread of the infection in the hope of saving as much of the harvest
as possible. In the case of potatoes, if the infection is widespread cut the whole
plant off at ground level and leave the earth undisturbed for at least two weeks
and more if possible, avoiding top watering, which may carry the spores down to
the tubers. After this the tubers can be lifted and stored, but will need to be
checked regularly to ensure that infection has not caused any to rot. If care is
taken, the loss will be only a small percentage of the whole.
Do not grow potatoes or tomatoes in the affected soil for at least three years. Pay
particular attention to sanitising the tunnel the following February, and dig out
any volunteer potato plants as they appear before they can release further
spores.
Botrytis
This mould affects a wide variety of plants and is a particular problem in poly-
tunnels, because of the high humidity. To avoid it, do not allow planting to
become crowded, remove all plant debris as it forms, and keep the tunnel well
ventilated, particularly in the autumn and when humidity levels are high.
 
Search WWH ::




Custom Search