Post by Admin on Jun 27, 2016 14:26:50 GMT
Scott on plots 17a and 17b has had to grub up the front rows of his potatoes because of blight. It doesn't seem to have affected his plantings in the upper half of his plot, but looks as if it may have spread to his neighbour.
Unfortunately this period of damp, humid weather is ideal for the development of blight. This is defined as a "Smith period" when on each of 2 consecutive days:
The minimum air temperature was at least 10°C, and
There were a minimum of 11 hours with a relative humidity of at least 90%
There are a lot of resources on the internet for the tracking of blight and reporting it happening. There is a toolbox here potatoes.ahdb.org.uk/online-toolbox/fight-against-blight-tool
In the past it was common practice to spray preventatively using Bordeaux Mixture, which uses copper sulphate as a key ingredient. Pressure from the agricultural lobby for strict controls has led to this being withdrawn from sale, although commercial growers now have a range of anti-fungicidal sprays that they can be licensed to use. The allotment holder and the gardnere are at a great disadvantage by this legislation,
Many people advise that you can leave potatoes in the ground even though blight is widespread in the foliage and stems (haulms), provided that these are cut down to within an inch or two of the earth. This will prevent the virus being spread by the breeze to your neighbours, and while the potatoes may not grow much larger they should not carry the disease if lifted at their normal harvesting time. The haulms should be collected and taken to the council dump or consigned to green bins. The council dumps will heat all waste to a temperature that will kill off the blight spores - do not place the stems or any spoilt potatoes in your own compost heap because this will only breed the virus to remain dormant till next Spring.
If any other plotholders have different advice or suggestions please add to this thread: we need to spread good practice wherever it comes from.
It has been tough for potatoes this year, with the late cold snap and now the blight, but if you do find the problem on your plot, please let your neighbours know at once so that they can take action. Remember, too, that tomatoes are of the same family and the virus will quickly spread to them.
Unfortunately this period of damp, humid weather is ideal for the development of blight. This is defined as a "Smith period" when on each of 2 consecutive days:
The minimum air temperature was at least 10°C, and
There were a minimum of 11 hours with a relative humidity of at least 90%
There are a lot of resources on the internet for the tracking of blight and reporting it happening. There is a toolbox here potatoes.ahdb.org.uk/online-toolbox/fight-against-blight-tool
In the past it was common practice to spray preventatively using Bordeaux Mixture, which uses copper sulphate as a key ingredient. Pressure from the agricultural lobby for strict controls has led to this being withdrawn from sale, although commercial growers now have a range of anti-fungicidal sprays that they can be licensed to use. The allotment holder and the gardnere are at a great disadvantage by this legislation,
Many people advise that you can leave potatoes in the ground even though blight is widespread in the foliage and stems (haulms), provided that these are cut down to within an inch or two of the earth. This will prevent the virus being spread by the breeze to your neighbours, and while the potatoes may not grow much larger they should not carry the disease if lifted at their normal harvesting time. The haulms should be collected and taken to the council dump or consigned to green bins. The council dumps will heat all waste to a temperature that will kill off the blight spores - do not place the stems or any spoilt potatoes in your own compost heap because this will only breed the virus to remain dormant till next Spring.
If any other plotholders have different advice or suggestions please add to this thread: we need to spread good practice wherever it comes from.
It has been tough for potatoes this year, with the late cold snap and now the blight, but if you do find the problem on your plot, please let your neighbours know at once so that they can take action. Remember, too, that tomatoes are of the same family and the virus will quickly spread to them.
