Potato Blight – Phytophora infestans - is one of the worlds most widely know plant pathogens largely because of the devastating social effects that followed after the destruction of the Irish potato crops in 1845-1850.
Unfortunately, even after over 150 years of research, there is still no known cure for this dreadful disease even though there are now many chemical available that can control its spread. So in light of this – and in an attempt to eat a better quality of food - perhaps the best method of control is to try and avoid an infection of Potato Blight in the first place. Below is a list of the best cultural and organic practices which will reduce the incidence of infection by this highly invasive and damaging fungus.
1. Any plant material or debris that is believed to have been infected by blight should be burned to prevent the risk of further infection.
2. Effective ‘earthing’ up can help protect the underground tubers from being infected by soil borne blight spores. Although these spores can survive in the soil for several weeks, they cannot penetrate deeply into it. You could also try and secure polythene sheeting under the plants to act as an effected barrier against the spores from entering the soil.
3. If you have the space available consider increasing the distance between tubers at planting time. This will allow a better circulation of air and will reduce the conditions of high relative humidity necessary for the effective formation of viable blight spores.
4. Remove all ‘ground keepers’. These are infected tubers which remain as weeds from previous crops. Either remove and burn them or change your next crop to cereals.
5. Avoid storing potatoes anywhere that may be damp. Although your crop may not be infected, you may be providing ideal conditions for an infection to take hold that can blow in from infected neighbouring potatoes.
6. Do not water from overhead when blight is actively sporing on the foliage as this can provide ideal conditions for these new spores to leech through the soil and infect the tubers.
7. Never lift your crop when there is evidence of blight on the foliage. Remove and burn infected foliage first to reduce the infection from being transfer to the tubers as they are lifted from the soil.
8. Problems with blight are normally far worse during the higher humidities of late summer and early autumn. Therefore losses from blight can be reduced and even avoided by encouraging the tubers to crop earlier. This can be achieved by chitting the seed at the earliest possible time.
9. If you believe that the use of traditional copper fungicides is within the bounds of organic gardening then you can use them to control the disease should a serious outbreak occur. However you must be aware that even though many chemicals have been developed that can effectively control potato blight there are as yet no methods that can actually kill it.
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