Potatoes are actually quite robust plants. Nevertheless, they are susceptible to various diseases and parasites. Read here what these are and how they can be combated.
Many hobby gardeners who have some space in their garden grow potatoes. These taste much better from your own garden than from the supermarket next door.
But if you plant your own vegetables, you have to expect that various diseases and parasites can spread.
Potatoes are particularly susceptible to pests if the soil is too dry in summer. But even on a surface that is too damp, mushrooms in particular have an easy time of it.
Today we briefly introduce the most important potato diseases and how you can recognize and combat them.
The 5 most common potato diseases
1. Herb and tuber blight
This blight is most common in potatoes. It destroys up to 30 percent of the potato harvest in our latitudes. Good table potatoes are particularly sensitive, here the harvest failure can even be up to 50 percent. This fungal disease is a very old disease. Over 150 years ago, entire populations were destroyed by this mushroom in many places. The tubers rotten and many people had to starve to death.
The fungus needs a moist environment to spread. Even when the leaves are formed, there is a risk of infection and, especially in warm, damp weather, the spreading progresses rapidly.
On the leaves you can see brown, slightly sunken spots, on the underside of the leaves there is a white coating. In the summer, when it is warm and humid, the spores of the fungus spread in no time.
Combating it is practically impossible in summer. If the herb of the potato plant dies, the fungus also perishes. But in the meantime, it has long since settled on other potato plants. You can only prevent late blight. When planting the potatoes, you should pay attention to resistant varieties, inferior varieties are much more susceptible to fungal infections.
Optimal fertilization of the potato plants is also extremely important, the plants are much more susceptible to too much nitrogen. If the weather is very humid in late summer, you can hardly avoid the use of chemical agents.
2. The potato scab
In contrast to tuber blight, potato scab is not caused by fungi, but by bacteria. These bacteria called Streptomyces scabies are found in all areas of Germany. However, they mainly affect potatoes that are grown on a light sandy soil. The pathogens penetrate into the growing tubers, especially during the first 14 days of the tuber attachment an infection takes place. Especially when the floors are very dry due to high temperatures.
Since the pathogen relies on a lot of oxygen, it is particularly easy to play on loose soils. The bacteria develop more easily even at higher pH values, so that a value of less than 5.5 is rarely affected by potato scab. Basically, the scab is not bad, there is hardly any loss of harvest and the taste of the tubers does not suffer. The problem with such scabbed areas is only the fact that other parasites can penetrate there particularly easily. If you later store these potatoes, they will shrink faster.
You do not recognize the potato scab early on because there is nothing to see on the herb. Only the tubers are affected. There are brown spots with cracks. If the infestation increases, they merge into larger areas that are scabbed. Sometimes the symptoms remain superficial, but the scab can also work its way into the tuber.
You cannot fight this disease directly, corresponding pesticides are not available. You should therefore definitely grow resistant varieties. Previous green manuring with rye, sweet peas or alfalfa is also helpful. You should not grow beets after the potatoes, because these crop rotations also promote infestation.
The plants should be watered at the time of the bulb formation, the soil should not be cultivated if possible, so that no loosening takes place. The potato scab is not a serious infection in private gardens because it does not make the tubers inedible.
3. The black legs
Black legs can also be more common in potato plants. Just like tuber wet rot, black legs are caused by bacteria. You only have to reckon with crop losses from a certain degree of infestation. Infection is particularly common in heavy soil, because it can easily cause waterlogging. There are also certain types of potatoes that are much more affected, including "Satina", "Adretta" and "Nicola".
Parts of the plant wither, turn yellow and can eventually die. Especially the stem is damaged, at the base of which you can see the typical black discoloration. The plants are easy to pull out of the earth, and there is a pungent smell.
Fighting black legs is hardly possible, so prevention is a top priority. This begins with the selection of the most resistant varieties.
With watering you should hold back a bit in summer. This is only indicated if the drought persists. Wait two to three weeks after the above-ground parts of the plant have withered before harvesting, only then the shell of the tubers is sufficiently hard. In the case of potatoes, you should definitely avoid fertilizing with stable manure.
" Tip: Annual crop rotation can be a good preventive measure.
4. The dry spot disease
The drought spot disease is also a fungal infection. The potato plants are particularly affected by dry, warm weather in summer, and tomatoes are also affected.
On the underside of the leaves there are brown, small spots that also have concentric rings. The spots are often also outlined in yellow.
The disease can not only manifest itself on the leaves, but also spread to the tubers. The wind and rain spread the fungal spores, they can survive the winter even in the dead parts of the plant and then cause a new infection in the coming year.
Infested leaves should be removed immediately, and good ventilation of the potato plants must be ensured. Sometimes you can't avoid the use of chemical pesticides. For example, the Consento tomato and mushroom protection or the copper mushroom protection from Gesal are helpful.
5. The potato crab
A fungus is also responsible for potato cancer, namely Synhytrium endobioticum. The infestation occurs on the stem base and on the tubers.
It is no coincidence that the infection got the name because it leads to overgrowth that resembles cancerous tumors that look like cauliflower. These cell growths can vary in size and reach the size of a fist. At first they are still light, but later they turn darker in color, then a black powder emerges.
" Note: Even if the potatoes are stored later, the infection can continue. The upper parts of the plant can be perfectly healthy while the tubers are already rotting. Potato cancer is a notifiable disease; cultivation on the affected area may only take place again after the absence of infection has been proven.
The infestation can be particularly severe in cooler, damp areas. Combating potato cancer is not possible, and chemical agents are also not available. You can only prevent this by using resistant seedlings and paying attention to crop rotation. Potatoes should therefore only be grown in the same place every four to five years.