Potato Alternariosis is a fungal infection of a plant that affects stems, leaves, and tubers. In Russia, due to this disease, up to 5% of the vegetable crop is lost annually. Most often, the pathological process starts in mid-June and develops throughout the summer.
General description of the disease
Alternariosis is a disease that occurs under the influence of mold Alternaria. The optimal conditions for the development of this microorganism are air temperature in the range of + 22-26 degrees and the presence of drop moisture for at least 2 hours.
Alternariosis is widespread in Belarus and Russia, especially in the Far East, in the western and central regions of the European part of the country.
The fungus is active at temperatures between + 7-12 degrees, dies at temperatures below -30 degrees. A pathogenic fungus overwinters in soil at a depth of not more than 5 cm, on infected plant debris. The viability of this microorganism depends on temperature, as well as an indicator of environmental humidity.
The disease is especially active on the lower and middle leaves of the stem in early July. Usually the fungus affects the stems and leaves, sometimes spreading to tubers.
Alternariosis is also called dry spotting. Most often, this disease affects early ripe varieties of potatoes, while mid- and late-ripening species suffer from a fungus much less frequently. At the same time, the decrease in yield in early varieties is much weaker.
Currently, there is no variety that has full resistance to alternariosis, but there are known types of potatoes that have increased resistance to it. These are Adretta, Master, Spark, Lyubava, Filatovsky, Gala, Lugovskoy, Lasunok, Svitanok, Bryansk delicacy, Fairy tale, Lapis lazuli and some others.
This disease is not unique to potatoes: the disease affects other plants, including those belonging to the nightshade family. In addition to potatoes, alternariosis also affects cabbage, tomatoes, eggplant, zucchini, carrots, onions, sunflowers and peppers.
Most scientists believe that alternariosis affects mainly weakened plants, but this pathogenic fungus is also found in crops that at first glance are completely healthy.
Routes of infection, risk factors
The main reason for the spread of dry spotting of potatoes is the entry of mycelium and Alternaria fungal cells onto tubers. This can happen during the planting period, when the mycelium preserved on the remains of plants and old tubers gets onto the tuber.
Fungal spores are carried throughout the summer and autumn. They fall on the potatoes with the wind, raindrops. Some insects also act as carriers.
Infection occurs as follows:
- the pathogen, getting on the surface of the plant, grows into it, penetrating through the stomata and damaged epidermis;
- in the intercellular spaces, a mycelium is formed, which, as it grows, releases acid, which has a detrimental effect on the tissue of the aerial part of the potato bush;
- the destructive process reaches the tubers, the lesion is expanding.
The pathogenic fungus Alternaria causes necrosis of the leaf apparatus, which leads to premature death of the entire plant. Over the entire period of potato development, several generations of a pathogenic fungus may appear. In an infected plant, respiratory and nutritional functions are impaired.
Factors that increase the risk of developing the disease are:
- lack of mineral substances in the soil - nitrogen and potassium;
- excess phosphorus;
- insufficient humidity;
- increased air temperature;
- improper preparation of seed material for planting;
- stagnation of water for more than 2-3 hours during irrigation, natural irrigation (rain);
- infection of tubers with viruses even before they land in the soil;
- weakened plant immunity;
- growing potatoes along with other nightshade crops infected with Alternaria (mainly tomatoes);
- exposure to parasites.
The symptomatology of this fungal disease manifests itself most clearly in hot weather, which alternates with heavy morning dew and rain.
The incubation period of potato alternariosis is an average of 3-8 days. If weather conditions are favorable for the development of the disease, then the symptoms appear within 3-4 days. The first symptoms are usually found on relatively young plants whose bush height reaches 15-20 cm.
Signs of Potato Alternaria
The first manifestations of a fungal disease can be considered when the bush grows 20 cm in height.
The defeat of the fungus is expressed in the following symptoms:
- The formation of small black spots on the leaves. Their feature is the presence of concentric circles and a weak black coating on the underside of the leaves. Spots usually appear 3 days after infection. Over time, the diameter of the spots increases. On the surface of these foci there is an olive velvety coating. As the disease progresses, the spots merge and can soon cover the entire surface of the leaf.
- The fragility of the leaves, as a result of which they die.
- The formation of dark spots on the tubers. Potatoes are rarely affected by alternariosis.
- The presence of areas of rot in a halved tuber.
- The appearance of deep wrinkles in areas covered with dark spots.
On stems and petioles, a fungal disease manifests itself in the form of strokes that connect and form solid spots. They are elongated 3-5 cm long, slightly immersed in the stem tissue.
On seeds, alternariosis manifests itself in the form of black mold. The disease negatively affects the germination of seed material.
If infection with alternariosis occurred during harvesting against the background of contact with infected root crops, the symptoms of a fungal disease will appear no earlier than 2 weeks later.
Ways to combat the disease
To combat alternariosis, various chemicals are used that fight the pathogen of fungal disease.
With this disease of potato, such chemical solutions are effective (0.2-0.3%):
- Cupricole;
- Profit;
- HOM;
- Newcomers;
- Cuproxate;
- Thanos;
- Albite;
- Metaxil;
- Utan;
- Abiga Peak;
- Unomil MC;
- Oxychom;
- Acrobat MC;
- Pencoceb.
Each of the drugs must be used in a strictly defined dosage. The method of application is also different. For example, the Acrobat MC is sprayed on the bushes up to three times during the potato growing season, and Albit - twice a season, during the period when the bushes close. The exact dosage is indicated in the instructions for the tool.
Also, plants with a fungal disease can be treated with copper chloroxide at a rate of 24-32 g per hundred square meters.
Chemicals are very toxic, therefore precautions must be observed when working with them. It is important to follow the recommendations specified in the instructions, use personal protective equipment, after working with the drug, change clothes and wash. During spraying, you should not smoke, eat, drink.
To avoid the effect of addiction, you need to alternate drugs for the treatment of diseased plants.
It is necessary to treat a fungal disease, since in the absence of measures, a significant part of the potato crop can be lost.
Preventative measures
To prevent the development of this disease, it is necessary:
- be sure to remove from the site, and then destroy the remains of diseased potatoes;
- deep plowing of the earth - this contributes to the decomposition of infected plant debris;
- observe crop rotation: this means that a certain type of potato needs to be returned to its original place of planting after 3-4 years;
- plant only healthy potatoes, inspect each tuber before planting;
- in the autumn period, carry out deep plowing of the soil - not less than 50 cm;
- treat the tubers with special compounds before planting that prevent the development of alternariosis: the most popular are Integral, Skor, Acrobat, Bactofit, Agat-25;
- carry out the first spraying of bushes with an antifungal agent at the stage of closing the tops in rows;
- before digging potatoes, mow the tops to prevent the pathogens from entering the tubers;
- plant potato varieties that are resistant to alternariosis: Resource, Victory, Master, Blue, Adretta, Bronnitsky;
- fight vectors of the fungus, which are aphids and other insects;
- separate diseased potatoes from healthy ones, prevent their joint storage;
- Do not plant potatoes next to tomatoes affected by alternariosis.
Throughout the growing season, it is necessary to monitor the condition of the potato and take measures at the very first symptoms of a bush damage. The sooner you begin to act, the more likely it is to keep the crop.
Alternariosis is a disease that spreads to nightshade crops. It affects not only the aboveground part, but also the tubers. To prevent the development of the disease, you need to process potatoes with special preparations. If it has already spread to the plant, you need to process it with special chemicals as soon as possible.