What to look forTypical symptoms of blight are dark brown or blackish, round patches, appearing on leaves, particularly around the leaf margins at first, and on stems. Tubers develop dark, sunken areas which may extend to cover the whole potato, giving a dry firm rot. Other fungi and bacteria may invade the tuber to produce a wet, foul smelling soft rot. Seemingly healthy tubers may rot latei
when in store.
The disease survives the winter in infected potato tubers which survive the winter in the soil or in discarded heaps' When these grow the following season the foliage produces massive quantities of spores which are spread on the wind.
Tips for fighting Potato Blight
- Plant good quality seed tubers from a reliable source, and especially don't plant any from a crop that was infected with blight.
- Plant early vareities early, as most are very prone to blight, so that they can be harvested before blight starts, which is usually in July.
- Plant main-crop varieties that are slow to develop blight such as Cara, Stirling, Teena, Torridon, Remarka and Romano.
- Recent research has shown that growing alternating rows of different resistant varieties can improve their performance.
- Early main-crop varieties are more likely to produce a reasonable crop before blight appears.
- Remove potential sources of infection by harvesting all tubers, even the tiniest.
- Also never abandon old tubers around the garden or allotment, or try to compost them
- Instead they are best burned, put in the dustbin, or buried deeply (over 60cm/ 2ft).
- Actually, infected potato foliage may be composted in a good active compost heap.
- Space plants widely to reduce humidity levels within the crop. This is because blight spores can only infect healthy leaves when wet.
- Always earth up potatoes to reduce the likelihood of spores washing down from the foliage onto tubers.
- If blight strikes: The disease may not spread through the crop if the weather turns dry.
- So during warm damp conditions immediate removal of all blighted leaves can slow an epidemic.
- However if the crop is badly infected, it is advisable to cut off all the potato foliage. This will help prevent spread to the tubers.
- In such a case don't harvest the crop for at least three weeks. By which time tubers will have thicker skins and blight spores on the surface should have died.
- Always check stored tubers regularly, and remove any that are rotting.