Leaf phyllosticta

The life cycle of the fungus is closely linked to plant debris, where it survives the winter in the form of pycnidia or mycelium. In the spring, with the onset of favorable weather, the fungus releases spores that are dispersed by wind and rain splashes.

The fungus enters plant tissues through stomata or mechanical wounds on the epidermis. Once inside, the mycelium begins to develop, secreting toxins that suppress the plant's immune system and degrade cellular tissues.

As the disease progresses, new fructifications called pycnidia form on the affected areas. These appear as tiny black dots, visible to the naked eye, which serve as the source of secondary infection throughout the growing season.

The pathogen is highly adaptive. By forming micro-pycnidia, the fungus can maintain its viability for long periods under adverse environmental conditions, waiting for the host to resume its growth.

The first signs of infection appear as small spots of irregular or circular shape on young leaves. The color of these affected areas ranges from light brown to deep brown, often bordered by a darker rim.

Over time, the center of the spot may fade, becoming grayish or whitish due to the destruction of chlorophyll-containing tissues. The leaf takes on a characteristic mosaic appearance, significantly reducing its photosynthetic capacity.

Black, pinhead-sized structures called pycnidia appear on the surface of the necrotic spots, primarily on the upper side of the leaf. This is a key diagnostic sign that distinguishes phyllosticta from other leaf spot diseases.

In cases of severe infection, spots merge, covering large areas of the leaf blade. This leads to premature drying and mass leaf drop, which weakens the overall health of the plant significantly.

Infection can also affect leaf stalks and petioles, forming elongated brown necroses. This disrupts the transport of nutrients and water to the leaf blade, accelerating its degradation.

The development of the infection is favored by high humidity, exceeding 70-80%, as well as frequent rainfall or heavy dew. Liquid moisture on leaf surfaces is necessary for the fungal spores to germinate.

The optimal temperature range for the pathogen's active reproduction is between +20°C and +28°C. This period marks the peak of disease spread in orchards and gardens.

Dense plantings and a lack of proper crown aeration create a microclimate with high humidity, which is ideal for the incubation of spores. Poor air circulation significantly accelerates the development of the disease.

Weakened plants, suffering from nutrient deficiencies or stressed by adverse weather conditions, are much more susceptible to infection than robust, healthy specimens.

Poor garden sanitation, such as leaving fallen leaves under trees or bushes, guarantees the persistence of the infectious background for the next season.

The primary damage lies in the sharp reduction of the photosynthetically active surface area of the leaves. The plant does not receive enough energy for growth and fruit formation, leading to yield loss.

In fruit and berry crops, the disease promotes premature aging of the plant. This affects the formation of fruit buds for the following year, reducing both winter hardiness and the total productivity potential.

The loss of leaves in mid-summer triggers secondary shoot growth, which may not harden before the onset of frost. This often leads to the freezing of young branches during winter.

The economic impact is significant, as epiphytotics can result in the loss of 30-50% of the harvest. The quality of remaining fruits also declines; they become smaller and lose their flavor profiles.

Prolonged phyllosticta infection can lead to the gradual drying of individual skeletal branches and even the death of the entire plant if control measures are not implemented.

Prevention begins with thorough sanitary cleaning of the plot in autumn. It is necessary to collect and destroy (burn or bury deeply) fallen leaves, where the fungus's pycnidia overwinter.

Timely pruning and thinning of crowns ensure good ventilation, which prevents the stagnation of humid air and reduces the probability of spore settlement on leaves.

• Apply copper-based fungicides (Bordeaux mixture) during the bud burst stage.
• Use systemic fungicides at the onset of symptoms during the growing season.
• Regularly apply fertilizers to boost the plant's natural immunity.
• Maintain proper spacing between plants during planting.
• Choose varieties resistant to fungal diseases.

The most effective long-term method is the use of disease-resistant varieties, which minimizes the need for intensive chemical treatments.

Upon detection of initial infection foci, it is recommended to selectively remove damaged leaves and branches, followed by tool disinfection to prevent the spread of spores across the plot.