The great Irish famine of the mid-19th century shows us how vulnerable potatoes can be when it comes to disease. Potato blight, caused by a rampant fungus caused a massive crop failure throughout Ireland, leading to famine and starvation.
Many of those who survived the famine decided to emigrate to far-off lands like North America and Australia, leading to a drop in the Irish population of some 50%.
Hybrid Potatoes can Resist Disease
Of course it was the common so-called Irish potato that was affected by the terrible blight. So it is not surprising that horticulturists decided to do what they could to try and “improve” the common potato.
Luther Burbank, an American horticulturist, is credited with having developed the first disease resistant hybrid potato. He called it the Russet Burbank potato and then, after selling the rights to it, went off to Santa Rosa with the proceeds. It was there that he established what is now a world-famous experimental farm.
Since then many different varieties of disease resistant potato have been bred (and I’ll talk about these in another post). Furthermore, most countries have standards that certify potatoes that are disease-free. If possible these are the seed tubers that you should plant.
Diseases Potatoes are Prone to
Unfortunately potatoes are prone to many diseases, including various leaf diseases. Insects often transmit viral diseases, but bacteria and fungi are also problems. These are just some examples:
· Potato scab, which affects the appearance of the underground tubers, is a very common fungal disease that affects potatoes. You can avoid it by ensuring the pH of your soil is between 5.2 and 5.5 and by keeping the soil relatively dry and always well-drained.
· Black dot is a fungal disease that causes wilt and rotting. It is encouraged by poor soil and bad drainage.
· Black scurf is another fungal disease, attacking underground. Good management should help you avoid this; unfortunately there are no varieties that are specifically resistant to it. Silver scurf is another type, but this usually occurs during storage.
· Early blight is also caused by a fungus. You can identify it by little dark spots that form on the leaves, which then turn yellow and dry, and then fall off. It is a major problem which is exacerbated by overhead irrigation.
· Late blight is another fungal disease, and is spread by wind and rain – and is worsened by overhead irrigation.
· Mould can be quite a bad problem, again because of moist condition and overhead watering.
· While wilts may be caused by a fungal disease, sometimes it is caused by bacteria. Either way it’s bad news. Healthy plants shouldn’t be attacked by wilts (of which there are several types), but using disease-free stock is your best protection.
· Blackleg disease is a rather horrid bacterial disease and one that may attack early on in the growing season. Again planting disease-free seed will usually avoid the problem.
How to Avoid Diseases from Infecting Your Potato Crop
Happily there are steps that you can take to avoid these problems in your potato patch. For instance weeds can be a source of disease, so these should be diligently removed. Aphids also carry diseases, so keep an eye out for these and use an organic spray if you spot them (spray in the evening when the good bugs aren’t usually around).
Crop rotation is an excellent way to prevent infections and diseases from one season being passed on to the next. Just remember that you should plant something that belongs to another family, because plants in the same family – brinjals, tomatoes, peppers, and so on – suffer from the same problems.
Feeding the soil with organic compost or manure is another safeguard, because good quality soil encourages good bugs.
Planting cover crops like wheat or barley is another safeguard, although this is only really an option if you are able to plant a field of potatoes. Alternatively you could plant one of the brassica species that grows through winter; mustard, cabbages, and canola are all brassicas that will help to minimise disease and control pests in your potato patch.
While mulching is always good, when it comes to potatoes, make sure you don’t mulch right against the plant as this may cause the stem to rot or even affect the leaves of the potato.
Too much nitrogen in the soil is also a disease risk.
Overhead sprinklers tend to exacerbate problems, so if you are able to, rather install a drip system or soaker hoses. If you’re watering with sprinklers, do so early in the day because wet leaves seem to invite disease at night; water splashing on the leaves also helps to transmit diseases.
If your potato plants look as if they are wilting, but the weather is cool, check for disease.Tags: black dot, black scurf, blackleg disease, crop rotation, disease resistant, hyprid potatoes, mould, planting cover crops, potato blight, potato scab, potatoes, Russet Burbank potato, wilts