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Potato Council on Potato Blight



 Watch Out for Potato Blight

 Gardeners and allotment owners are being urged to be on the look out for potato blight this summer, the disease that caused the Irish potato famines in the 1840s. Experts say that more and more outbreaks of blight are originating from allotments and gardens. These can spread to other gardens and allotments, but also affect commercially grown potatoes.

 Gary Collins, Technical Executive with the Potato Council, said: �In the current climate more people are growing their own potatoes. As potato blight is a major concern to the industry, we keep a check on where outbreaks are coming from. Between 2007 and 2008 the number of outbreaks from allotments and gardens more than doubled. Because potato blight can spread very easily over large distances, everybody needs to keep a close eye on their potatoes.  Not only can it can reduce the quality of your home-grown crop, but also your neighbour�s crop, and the local farmer�s crop too. A little knowledge and effort can go a long way to reducing the impact of this disease�

 Blight is most likely to appear between July and September, particularly when the weather is warm and humid. Gardeners should look out for dark brown or blackish patches or lesions on the top of the leaflets [1], often surrounded by a pale yellow halo. These lesions may also be found on the stems [2]. Under humid conditions, there may be a downy white coating that looks like fine cotton wool developing on the underside of the leaflets, or again on the stems. Blight spores released from this white coating is how the disease spreads from the foliage to other plants, or down on to the soil, where they can infect the tubers, causing sunken areas on the potato surface, and a chestnut-coloured rot under the skin.

 If you discover what looks like potato blight you should snip off the leaflets, or even whole stems to stop the disease spreading and remove them from the crop. If vigilant, this may slow the spread to a point where the crop is unharmed, and you will have done your bit to help reduce the spread of blight. The potatoes can still be harvested after two to three weeks. Make sure you remove all the potatoes from the ground, and do not leave any in the soil or on garden tips.

 Tips for preventing blight include:

         Always buy your seed potatoes from a reliable source

         Choose a variety that is less susceptible to blight

         Ridge the soil well after planting your potatoes

         Mulch to reduce the amount of water required

         Water the soil and not the potato foliage

         Harvest all your potatoes � even the tiniest ones



 To find out more about potato blight, visit for an in-depth fact sheet. On this site, you can also register free to receive weather warnings that let you know when the conditions are right for the spread of blight - known as a Smith Period, or that there may be blight in your area. These are sent by email and as a text message.


Note to editors

         Potato Council is part of the Agriculture and Horticulture Development Board working on behalf of British potato growers and purchasers to promote potatoes.  Potato Council is funded through a statutory levy on 3,000 potato growers and potato trade purchasers and aims to support the British potato industry 

         Please below a Fact Sheet with more information on blight.

Potato Blight � The Facts

          Potato blight is the most important potato disease.

         Potato blight is a fungal disease spread by spores.

         Potato blight is most likely to appear between July and September, when the weather is at its warmest.

         The signs of potato blight are dark brown or blackish patches on the leaves, often surrounded by a pale yellow halo. On the underside of the leaves there may be a downy white coating of spores in moist conditions, particularly at night. These blight lesions may also be on the stems.

         The blight can spread from the foliage to the tubers, causing sunken areas of the potato, and chestnut coloured rot under the skin.

         Once blight affects a plant, the infection can easily spread given the right weather conditions.

         If the weather is humid, the spores that spread blight can spread over long distances.

         Between 2008 and 2009, the percentage of outbreaks of blight originating from allotments or gardens rose from 3.6% to 9.1%.

         Organisations such as Potato Council monitor conditions for periods when blight infection can spread most rapidly. These are known as �Smith Periods�, and occur when there are at least two consecutive days of temperatures of 10�C, and on each day there are 11 hours when the humidity is greater than 90%. You can find more information and register for forecasts at

         Gardeners who discover potato blight should remove the affected leaves or stems to prevent blight spreading to the potatoes. The earlier this is done the better. This will also stop the spores spreading. This may reduce the number and size of the tubers growing on the stem

         Tubers should be harvested after two to three weeks, and may be unaffected.

         Those growing their own potatoes can take a number of steps to ensure that reduce the likelihood of blight occurring:

o   Always buy your seed potatoes from a reliable source. Do not bring seed potatoes from another country, or save your own as they may be infected.

o   Some maincrop varieties show some resistance and are slow to develop blight.

o   Always remove all potential sources of blight. Harvest even the tiniest potatoes, and remove any potatoes that grow by themselves (volunteers).

o   Never abandon old tubers around the garden or allotment, or try to compost them.

o   Remove blighted tubers before storing, and always store your potatoes under dark, cool conditions.

o   Avoid planting in sheltered sites and plant in rows into the wind if possible.

o   If watering is required apply to the base of the plants, soil improvement and mulching will reduce the amount of watering required.

o   Blight spores on foliage are washed down through the soil to infect tubers. Earthing up potatoes, or mulching the soil with hay or straw can reduce levels of infection.

         Potato blight caused the Irish potato famines in the 1840s and led to widespread starvation.



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Name: ginny
Date posted: August 15, 2010 - 11:05 am
Message: Hi, I have discovered my entire crop of Nicola second earlies has potato blight. First plant "died" i thought last week. "nd yesterday and by last night every one of the 40 or so plants had shown the telltale leaves. Have dug up the entire lot today and harvested them. There were some plants with white cottony threads in the ground - looked a bit cobwebby. Some had clearly rotted soggy and largish potatos but other pots on the same plant were fine. Have saved the ok ones. Some ok ones had white spots like mould on which wipe off. These ok to eat?? Also found some half centimetre long white threadworm like creatures lurking with intent - are they related to the blight. Have read I should have waited before lifting the spuds after removing the tops -eek. What is the best thing to do - this is my first ever veg. on the plot after two years digging and ground prep. We have heavy clay soil and a lot of water from above - live in Devon!! Can I grow spuds on a different part of the same plot next year. Which might be better than Nicola and what should I do to prepare the soil. Can I grow other vegetables iminently on the soil I have just dug over. I think I have got all the spuds out but there are threadlike roots still in the soil. do I treat it first and then wait before planting something else. Have tried to stay off chemicals as want an "organic" plot if possible. If I have to use something to avoid infecting my plants next year I will. I would love some advice. Is there somewhere it would be helpful to record this incidence of blight for this area? Is there a central register of it each year?
Many thanks for your help. Sorry this is so long.