what does blight look like on potatoes

What Does Blight Look Like On Potatoes

At times, history classes may not have been easy to pay attention to, yet we have all heard of the potato famine that took place in Ireland. A disease that wiped out much of the population of the country is definitely worth taking a second look at.

Each plant and vegetable has its own personal pest and disease problems and blight is one of those for the potato. So, what is it and how do we ensure that our own gardens stay safe from this terrible disease?

This article will give you an idea of what blight actually is, how to prevent and manage it, but primarily how to recognize what does blight look like on potatoes.

What is potato late blight?

There are many different kinds of blights that can affect tubers and other plants, like tomatoes. A “blight” just means a disease whose symptoms will include a lesion or withering in the leaves or tubers of a plant.

Diseases that fall under the category of a blight will take effect rapidly and the entire plant will turn yellow and then die. In potatoes they will also cause rapid rotting of the tubers themselves.

Early blight and late blight in potatoes

There are two different types of blight that are commonly known to have a big impact on potatoes, potato early blight, caused by the fungus Alternaria solani, and potato late blight, which was the cause of the famine and what this article focuses on.

Potato Late blight

The scientific name of late blight is Phytophthora infestans, appropriately named for its very infectious spreading ability.
The blight is commonly known to many people as a fungus, but it is in fact and oomycete, or a water mold.

It is most closely related to algae and its life cycle is normally what can confuse people as it characterizes that of a fungus.

Appearance and symptoms of late blight

The disease spreads through the air and is fostered when weather begins to move towards a summer climate with warm and humid days. The worst epidemics are always known to occur as the days get warmer and the nights are cooler with mists and rains.

The first symptoms that will show up will be small brown dots on your potato leaves, or freckles, that will gradually spread out. These freckles will begin to form patches on the leaves as they merge together and will often be soft, like rotten plant material.

In many cases, the completely dead brown spots will be surrounded by growing yellow sections, which is when chlorosis is taking place.


Chlorosis is when chlorophyll, or the part of a plant cell that gives the plant its green coloring, is lacking.

While Chlorosis itself can be caused by many different diseases and lack of certain nutrients, it is also a well-known indicator of potato late blight.

White mould on leaves

Another indicator in very humid conditions is a fuzzy, white mold that will begin to grow on the underside of the infected leaves. Once the leaves have gone through the process of turning from yellow, onto brown flecks, and then patches, the leaves will curl up and will die, stopping photosynthesis from happening entirely.

What does blight look like on potatoes

The above ground symptoms aren’t the only way to figure out if your plant is really suffering from potato blight though. Many of these symptoms are common in displays from other diseases as well.

Digging into the mound of a suspected diseased plant will help to give you a clearer idea, especially if the infection is serious and has had a little time to develop.

On the outside, the infected tubers will have begun to form grey or even darker patches that will have started to rot and are slightly sunken in.
From here, chopping the potato open will revel the bulk of the damage with a mosaic of reddish-brown spots of rot spreading throughout the inside of the potato.

the appearance of blight on an infected potato

The mush that the potato will become will have the distinct smell of rotting food.
This step involving the potatoes will often be the last in the plants march towards death at the hands of the blight.

How long does it take for blight to ruin a potato crop

The whole disease can run its course in as little as five days if it has all of its desired conditions met.

How to prevent and manage blight in potatoes

To say you will prevent blight 100% is incorrect as it can infect any plant easily. The thing to do is to try to prevent blight from being a problem. To try to prevent blight we can explore two ways, either spray the potatoes with a blight spray or plant blight resistant varieties.

Blight resistant varieties

Nowadays, we have good blight-resistant varieties of potatoes that will generally manage to fend off the disease. Although in reality these are not really used, as we all have our own favourite varieties and these are usually are not blight resistant.

Blight spraying

The spores of blight are easily spread through strong winds as well as rain washout and can quickly travel a long distance.
The most common way of preventing blight is by a good spraying program – which usually takes place every 5 to 7 days. These blight sprays will help to protect the leaves and stems of the plants., and there are also sprays which have a systemic action – this transfers protection down into the potatoes in the soil.

black spots of blight on a potato plant leaves
black blight spots on leaves of potato plant

A good example of a blight spray would be Dithane – which i have listed at the end of this article. Or you can make your own blight spay – follow the link to this article

The blight spray should be sprayed before the disease infects the plants to be most effective, although there are sprays which allows you to manage the blight if it has already got into the plant.

These type of sprays dry up the leaves and stop the blight spreading any further
It is even more essential that the potatoes continue to be sprayed even after the disease is spotted to try to manage the blight and stop its rapid spread.

Remove blight infected tops

If signs of the disease have already been spotted, even if I don’t know if the infection is potato blight or not, I will play it safe by removing the spotted leaves.

Potato blight spores can be spread throughout the garden quickly, so if a plant or parts of a plant need to be taken out or disposed of, bury them in the soil or better still, put them into a tied bag in your bin and completely remove them from the area.

Removing these infected tops early will save the tubers, as long as the layer of soil over the potatoes is deep and the potatoes are well covered.
Infected tubers/potatoes can rot even after they have been harvested, even if they look completely intact beforehand.

Keep this in mind if signs of the disease have been spotted in your garden so you can be on the lookout to be able to immediately throw out any potatoes that begin to rot in storage as they will infect other potatoes around them.

This disease can sneak up on us, but I am sure after this we will all be prepared and ready to beat the blight! Good luck gardeners!