The current Irish weather conditions are ideal for Potato Blight and gardening expert Paraic Horkan has some invaluable advice on how to prevent and treat this devastating disease.
Potato Blight is one of the worst disease problems when growing potatoes. It can destroy plants overnight and infect the tubers causing them to rot in storage. Also, if your potatoes are stored in a sack or crate the blight will spread to infect each potato. Paraic explains that Potato Blight is caused by a fungus Phytophthora infestans.
This can also affect other members of the potato family, such as tomatoes. It spreads through the air and develops when the weather conditions are warm and humid.
The Potato Blight fungus is generally killed by cold weather, but there are some rare resistant strains that survive over the winter. Otherwise, the disease is present in infected tubers in the ground or your sack.
But remember, it can travel miles on the wind and there is very little you can do if the weather conditions are correct (above 10°C and 75% humidity) with recent rain causing wet foliage.
What to look for?
Paraic explains that the first thing you may notice is brown freckles on the leaves of the potato. Also they may have larger brown patches and a sort of yellowish border spreading from this patch. In a severe attack, you may find that all the potato foliage has become a rotting mass.
The tubers (the potato itself) are shrunken with dark patches on the skin. If you cut the potato in half, you will see brownish rot spreading down from the skin.
How to prevent Potato Blight?
There are a range of chemical treatments available, but Paraic recommends Proxanil Blight Spray. Proxanil works within the stems and leaves, moving up through all new growth. On newly infected potatoes, it can kill early blight spores to stop the blight from taking hold. Potatoes with early symptoms of blight can be cured with Proxanil. Paraic explains that for the maximum protection, you should spray Proxanil in dry weather, every three weeks and over a twelve week period in the summer.
Treatment of Potato Blight:
1. If you notice a small number of infected leaves (with brown patches), you can just remove them. But if you have a more serious infection, you need to cut off all the foliage and stems. You should place them in a bucket to stop the infection from spreading and dispose of them in a bin. If it is possible you should burn them.
2. Removing the foliage prevents the disease spore getting into the tubers. But this is only effective if the tubers are well covered with earth. You should cover over any exposed tubers to prevent blight from reaching them. This will also prevent sun and crow damage.
3. Spray with Proxanil as this has the ability of killing off early Potato Blight spores on new potatoes.
4. Leave the crop for at least two weeks. This will let the blight spores on the surface die and the potatoes develop a thicker skin.
5. After harvesting, check regularly for signs of blight and remove any suspect tubers at once from your store.
6. Lift the tubers and store in potato sacks in a cool dark area to use over the Autumn and winter period.
7. Ensure you purchase new certified seed potatoes next season as blight can remain active in tubers and can affect next year’s crop.
Growing Blight Resistant Varieties:
There are many blight resistant varieties of potato available. Paraic explains that the Sarpo Hungarian potato varieties have been recent developed to be extremely blight resistant. He recommends the Sarpo Mira as a wonderful blight resistant variety; it is floury, well flavoured and a terrific cropper. It is a nice red skinned potato with lovely white flesh.