What to do against tomato blight?

Tomato blight is one of the diseases that most frequently afflict this plant.Caused by a fungal pathogen, Phytophthora infestans, this tomato disease affects the plant with a series of easily recognizable symptoms that tend to begin with spots on the leaves, first gray-green and then brown, that expand very quickly.

In our guide today, we will look together at what tomato blight is, how to prevent and cope with it, and how the latest technology can lend you a hand to avoid any discomfort to your plant.

The causes of tomato blight

Downy mild ew is a fungal disease that affects many plants, but in the case of tomatoes it takes on particularly devastating characteristics, capable of endangering the very survival of this plant.

The pathogen responsible, Phytophthora infestans, is an agent that belongs to the Pythiaceae family and is the same one that caused the great Irish famine in the 19th century, devastating potato crops and causing very extensive damage that reduced the yield and quality of the crop for a long time. It is a very well known and very dangerous fungus, which proliferates under specific conditions and which it is good to recognize promptly in order to counteract it most effectively.

There are many environmental conditions, moreover, that can promote the proliferation of this agent and play a key role in the development of the disease.

First, we share in this in-depth discussion how downy mildew is able to thrive mainly in warm and humid environments, with temperatures between 10°C and 25°C. Thus, late spring and late summer are the preferred times for this fungus to become active and produce the damage to attacked plants.

However, prolonged rainfall, dew, and high humidity can also contribute to ideal conditions for spore activation: it only takes 10-12 hours of continuous moisture on the leaf surface to initiate infection, which then spreads rapidly through water and wind.

Consider, however, that the whole year can be a propitious time for infestation, as the spores of the pathogen can survive in the soil even during the winter, ready to infect crops again the following season. In fact, these are very cold-resistant spores that can live even in the soil under plants. Here, then, natural preventive remedies such as crop rotation and garden hygiene become essential.

Symptoms of tomato blight

Given the already established danger of tomato blight, it becomes very important to act in a timely manner and, therefore, to be able to identify signs of infection early as the first step for effective intervention.

The symptoms of blight occur characteristically on different parts of the plant:

• On the leaves: this is the part that is affected first. Necrotic areas with a discolored appearance form on them, changing from yellowish or greenish, then rapidly turning dark. If you look at the underside of the affected leaves, you can see a characteristic whitish mold, an unmistakable sign of the presence of the fungus and its reproductive structures.
• On stems and branches: dark areas with a rotting appearance but hard to the touch appear, growing to envelop the entire shoot. Lesions can impair nutrient transport in the plant, thus causing wilting of the upper parts.
• On fruits: not even fruits are unfortunately spared. Tomatoes affected by blight include both green and ripe tomatoes, on which large patches appear, with a wrinkled, bronze-tinged, sunburn-like appearance. The underlying flesh becomes stodgy and unfit for consumption, irreparably compromising the crop.

Complicating the evaluation scenario for the farmer is the fact that the symptoms of downy mildew can be easily confused with those of other diseases. However, there are some details that can more distinctly reveal the presence of this tomato disease: for example, Alternaria-another common fungal disease of tomatoes-can be distinguished from downy mildew because the spots are concentric, with well-defined edges and yellow halos at the margin.

The prevention of downy mildew

As in many plant diseases, prevention is the most effective and least costly activity.

However, there are several tools you can activate in order to create unfavorable conditions for pathogen development.

Of all of them, water management is the most important factor: therefore, try to reduce moisture around tomato plants by watering them at the base in the morning to allow them to dry out during the day. Instead, avoid watering the leaves directly. Help by adopting drip irrigation systems, rather than sprinkler, to significantly reduce the risk of infection by keeping the aerial part of the plants dry.

It then focuses attention on soil preparation, with the aim of preventing waterlogging in case of rain. Therefore, adopt deep spading to make the soil draining, preventing water stagnation, a favorable condition for fungus development.

Planting density and pruning are also two elements you should focus on: try to encourage air circulation between seedlings by maintaining the right spacing and thus reducing moisture between plants. Regular pruning, by removing the lower leaves that might come in contact with the soil, reduces the danger of infection by direct contact with spores in the soil. Therefore, remove the lower leaves that may touch the soil.

Finally, as we have already anticipated, crop rotation can also well be credited as another key preventive strategy: thus, avoid growing tomatoes or other solanaceous plants (such as potatoes, peppers, and eggplant) in the same soil for several consecutive years to reduce the presence of spores in the soil.

Natural prevention against tomato diseases

For farmers who prefer an organic approach to farming, there are Different preventive treatment options that respect the environment and health.

A first mention is certainly attributable to copper products, which are typically the most effective traditional solution allowed in organic farming. However, a conscious use of copper, which tends to accumulate in the soil, is essential: while it is indeed true that this natural fungicide can prevent and fight the disease compatibly with the organic approach, it should not be abused, thus making it advisable to alternate copper treatments with other solutions.

Other natural alternatives include herbal macerates such as horsetail and nettle, which have shown some preventive efficacy. Zeolites, which are natural materials with absorptive capabilities, are also useful in reducing moisture on the leaf surface and thus discouraging the appearance and proliferation of the fungus.

Another viable route is potassium bicarbonate solutions, especially if repeated once every ten days or so: the properties of very pure potassium bicarbonate allow it to prevent fungal diseases without releasing heavy metals into the soil.

The effectiveness of the Plantvoice system in preventing tomato diseases

In this scenario, the Plantvoice system represents a technological revolution in the protection of tomato crops from the many diseases that can compromise their productivity. Through innovative and noninvasive monitoring, the digital ecosystem in fact offers unprecedented protection against the fungal, bacterial and viral diseases that typically afflict this crop.

Our real-time sap monitoring technology forms the centerpiece of the Plantvoice system, allowing physiological changes to be identified before visible symptoms appear. In tomato crops, this approach is particularly valuable for early detection of blight, because it allowsearly identification of apical rot, often caused by nutritional imbalances or water stress, and monitoring of viral infections such as tomato mosaic virus (ToMV) before leaf symptoms appear. Especially important is also thedetection of abiotic stresses that may predispose the plant to pathogen attack.

The “sentinel plant” approach is particularly effective in tomato crops due to the genetic uniformity of commercial varieties. By installing the sensor on a representative plant, statistically significant sampling is achieved for areas of about half a hectare, drastically reducing the time required for traditional phytosanitary controls. A method that makes it possible to identify outbreaks of infection before they spread to the entire plot and to optimize phytosanitary treatments, applying them only where and when necessary.

TheAPI interface of the Plantvoice system enables integrated management of tomato health by correlating physiological data with weather conditions to predict fungal disease risk. The system enables automated scheduling of preventive treatments based on predictive models and provides complete traceability of phytosanitary interventions for production certification. Also crucial is theoptimization of irrigation to prevent water stress that promotes certain diseases.

How to treat plants if blight has already struck

So far, some useful nods to tomato disease prevention. But what to do when the first symptoms of blight are encountered?

In this case, prompt action must be taken to limit the damage and prevent the spread of the disease.

The first step is to remove theinfected parts: first, the diseased parts of the plant must be removed by cutting off leaves or entire branches affected by the fungus attack. It is very important to properly dispose of infected plant material, avoiding leaving it in the garden or composting it, so as not to encourage the dispersal of spores.

Next, a copper-based treatment can be carried out, which, as we have seen, is certainly the most effective solution even in the curative phase. The application should be done by carefully following the doses and timing indicated by the manufacturer, remembering that a maximum annual amount of copper metal per hectare is allowed in organic farming.

In the case of particularly severe attacks, in conventional farming settings, systemic fungicides such as those based on cymoxanil, metalaxyl or dimethomorph can be used, which are absorbed by the plant and translocated into the tissues, offering protection from within.

Other major tomato diseases to know about

Unfortunately, in addition to blight, tomatoes can be affected by numerous other diseases that it is important to know how to recognize for targeted intervention.

One of these is powderymildew, or white blight, which initially manifests itself as chlorotic (lighter) spots on the upper page of the leaves, until, over time, the unmistakable presence of white spots with a powdery appearance. Unlike downy mildew, powdery mildew can also develop in conditions of low humidity.

Alternaria is another common fungal disease that can be distinguished by the gray circular spots that appear on leaves, which tend to dry up quickly. Copper treatments effective against downy mildew generally have a positive effect against this disease as well.

Gray mold(Botrytis cinerea) occurs mainly in hot, humid environments and, if the plant is not properly cared for, causes the leaves to dry out and the tomatoes to die. It is particularly insidious in greenhouse crops.

How to control tomato blight

As we have seen in this guide, tomato blight-while a serious threat-can be effectively managed through an integrated approach that combines preventive agronomic practices, constant monitoring, judicious use of plant protection products, and selection of resistant varieties.

Thorough knowledge of the biology of the pathogen and the conditions that favor its development is the basis for a successful control strategy.