Potatoes are one of the most widespread and productive crops, but also among the most vulnerable to fungal and bacterial diseases and pest attacks, which can compromise yield and crop quality. For this reason, disease and insect management must be timely and informed.
In this guide, we’ll analyze the most common potato diseases and pests, the signs to watch for, and the most effective solutions for preventing and containing them using organic approaches.
The most common potato diseases
Potato downy mildew
Potato late blight is one of the most common and dangerous diseases, caused by the oomycete fungus Phytophthora infestans. Like tomato late blight , potato blight is favored by humidity, particularly rainfall lasting at least six hours, dew that keeps the plants wet for at least 12 hours, and temperatures between 10 and 24°C. These weather conditions are particularly dangerous for the spread of the disease, as the infectious agents are carried by the rain , contaminating the potatoes. Furthermore, the fungus spores can survive over the winter in infected crop residues left in the soil, in infected seed tubers, or in spontaneously growing plants. When the plants sprout, the pathogen reactivates, and the infestation can spread very quickly, especially in the presence of mild temperatures and high humidity.
The first symptoms usually appear on the basal leaves and in general can be:
- Pale or brown spots on the leaves, with yellowish halos.
- Whitish mold on the underside of the leaves.
- Browning and constriction on the stems , with loss of functionality and drooping of the plant.
- Depressed lesions on the tubers , brown in colour, often soft and smelly.
- Post-harvest damage , with rot appearing during storage.
If left unchecked, the disease can spread very rapidly, compromising the entire plot. Therefore, it is essential to prevent potato blight through several strategies:
- Carry out crop rotation, avoiding growing potatoes on the same land for 2-3 years.
- Choose varieties that are resistant or tolerant to downy mildew.
- Maintain adequate distances between plants to promote air circulation.
- Avoid excessive nitrogen fertilization.
- Prefer drip irrigation , avoiding wetting the leaves.
- Earth up to support the plant.
- Carry out preventive treatments with natural tonics, such as rock flour, propolis, lecithin or horsetail decoction.
To prevent downy mildew, you can use organic and environmentally friendly remedies that help reduce the spread of the pathogen without harming the environment. These include:
- Copper treatments.
- Bacillus subtilis : a bacterium that performs a biocontrol action.
- Plant extracts : for example, neem oil or horsetail extract, useful for strengthening plant resistance and reducing infection.
Black leg of potatoes
This pathology is caused by Pectobacterium carotovorum ssp. carotovorum , a bacterium that is very dangerous for potatoes. Blackleg can appear in the early stages of potato growth, causing yellowing of the plants and compromising tuber formation, or it can appear later in the growth stage with blackish spots at the base of the stems and tuber rot.
The bacterium thrives in rainy weather and poorly drained soil . It can overwinter in infected seed tubers and in the soil, making selection of the material essential to prevent the spread of the bacterium, especially when producing seed tubers yourself. To prevent or contain the infection, it is also possible to treat with copper-based products, use certified seed tubers, practice crop rotation, drip irrigation, earth up the tubers, and eliminate infected residues.
Alternaria
This disease is caused by the fungus Alternaria solani and A. alternata. Its aggressiveness peaks during late ripening . How does it manifest? The symptoms of alternaria are mainly spots on leaves and stems . They are characterized by concentric dark brown circles, caused by the sporulation of the fungus.
Here are the main prevention methods .
- Remove crop residues , weeds and wild plants .
- Use certified, pathogen-free seeds and propagating materials .
- Rotate crops , especially when spores that remain alive in the soil are the primary cause of infection. Crops such as wheat and barley are recommended to reduce the number of conidia surviving in the soil.
- Use plant varieties resistant to alternaria.
- Store the collected products at a temperature between 0 and 1° C.
- In the greenhouse: avoid high humidity levels.
Rhizoctoniosis or “White Calzone”
Another potato disease to watch out for is rhizoctonia solani. It is caused by the fungus Rhizoctonia solani . The most common symptom is the formation of small black or dark brown crusts , usually on the surface, isolated or in clusters. On shoots , the disease manifests itself as irregular, depressed, dark brown spots , which often impede plant growth in cultivated soil. Another symptom is known as ” white spot .” This involves a whitish patina or mold that tends to form on the stem, and in most cases is due to humidity. Finally, this disease stunts the plant’s growth and, in some cases, can cause its premature death, as the transfer of nutrients to the runners no longer occurs.
The main methods of defense in this circumstance include:
- Use semi-healthy tubers .
- Rotate crops so that potatoes or other highly contagious crops do not return to the same land for at least 4-5 years.
- Use pre-sprouted tubers or shallow sowing to speed up plant development in the early stages, especially when sowing is postponed due to adverse weather conditions.
Additionally, during the growing season, specific fungicide treatments can be carried out using Azoxystrobin . Finally, before or during sowing, antagonistic microorganisms can also be used (in both conventional and organic farming) such as Trichoderma asperellum and Pseudomonas spp. strain Dsmz 13134.
Fusarium wilt or dry rot of potatoes
Also known as “ dry rot ,” this disease, as the name suggests, causes potato tubers to rot. The fungus that causes it is Fusarium , which is also harmful to some aromatic plants .
Visually, it can be recognized by the rotten spots on the inside of the tuber. They often also have holes. Among the main causes are wireworms , which bore holes in the potatoes underground and allow the disease to develop, tuber splitting , or hollow hearts , which also allow the disease to spread. The causes are linked to a lack or, conversely, excess water . The solution is to water wisely. In the case of hollow hearts, the cause may also be an abundance of nitrogen, a problem that also affects aphids .
Bordeaux mixture is a very useful tool for combating dry rot in potatoes. We always recommend paying close attention to checking for the presence of wireworm larvae . Finally, we point out that, once Fusarium has been eliminated, the soil should not be used for growing potatoes for a few years, as the fungus spores remain active and, consequently, pose a risk to subsequent crops.
Potato parasites: Colorado beetle and Elateridae
Let’s now analyze some of the most common potato pests. The first is the Colorado potato beetle , also known as the Colorado potato beetle. It can quickly damage crops, making it a major concern among farmers. Another concern is its rapid reproduction rate. In particular, its larvae feed on potato foliage , and if left unchecked, it can cause complete leaf loss. Furthermore, they damage plant development and drastically reduce tuber yields. Prevention is crucial in this case too, and can be achieved through crop rotation or the planting of repellent plants ( marigold, calendula, and beans ). However, once the pest is already present on the potato, organic methods are the most effective way to eliminate it. These include Bacillus thuringiensis, neem oil, and various organic products.
In addition to this parasite, wireworms represent another danger for potatoes, as explained in the previous paragraph.
Tips for growing potatoes organically
For healthy and efficient organic farming, it’s essential to adopt some of the previously mentioned measures that promote plant growth and reduce the risk of disease. Here are the most important practices:
- Crop rotation : Potatoes should not be grown in the same soil for more than two consecutive years, to avoid the accumulation of specific diseases.
- Plant spacing : maintain a distance of at least 70 – 80 cm between rows to ensure good air circulation.
- Use of healthy seed tubers : To avoid the transmission of diseases, it is necessary not to use self-reproducing tubers, which could be infected.
- Irrigation control : the plants do not require abundant watering.
- Use of strengthening extracts : very useful for strengthening the natural defenses of plants.
- Treatments with natural tonics : Products such as propolis, rock flour, and lecithin can stimulate the natural defenses of potato plants. Diluted in water and sprayed on the above-ground parts of potatoes, they can reduce the likelihood of developing diseases.
Using these strategies, it is therefore possible to grow healthy and nutritious potatoes without the use of pesticides or chemical fertilizers.
Recommended biological treatment techniques
Organic potato disease control relies on natural and sustainable methods that protect the plant and the environment. To grow healthy crops, potatoes prefer well-drained, nutrient-rich soil . They should be planted about 10 cm deep and about 50 cm apart. Regular watering is essential, especially during periods of drought, and it’s important to choose a potato variety suited to your climate and soil. Finally, after harvesting, it’s best to store them in a cool, dark place to prolong their shelf life.
Organic potato treatment also focuses on prevention , so after planting potatoes correctly, it is a good idea to adopt some of the techniques:
- Copper treatments : for example Bordeaux mixture.
- Bacillus thuringiensis : This bacterium acts as a biological insecticide and does not cause harm to humans or the environment.
- Beneficial insects : introducing natural predatory insects is an organic method that allows you to preserve the natural balance, without using chemical pesticides.
- Natural macerates and decoctions : nettle macerates or garlic extracts can be used as natural pest repellants.
- Chromotropic traps : they are a useful tool for monitoring and controlling the presence of parasites such as aphids and beetles.
- Regular monitoring : Constant observation of plants is one of the fundamental principles of organic farming. Periodically checking leaves, stems, and soil allows you to promptly identify symptoms of stress, nutrient deficiencies, or pest infestations, allowing you to intervene immediately with natural methods.
Growing potatoes organically can be time-consuming, but it offers numerous benefits in terms of flavor, nutrition, and environmental sustainability.
Intelligent water management with Plantvoice
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Plantvoice thus enhances plant health and crop sustainability , transforming irrigation into a conscious, efficient and environmentally friendly process.
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