Delphinium Ascochyta blight

The primary symptom of the disease is the appearance of characteristic spots on the leaves of the Delphinium. These spots can have a round or irregular shape, often framed by a dark margin.

Over time, small, barely visible dots appear in the center of the spots. These are pycnidia, the fruiting bodies of the fungus, which look like tiny black or brown grains.

As the disease progresses, the affected leaf areas begin to turn yellow and eventually wither. The leaf blade may curl, significantly reducing the decorative value of the plant.

The infection can spread to the plant stems, causing elongated spots to form. This weakens the stem and can lead to it breaking under strong wind conditions.

In cases of severe infestation, premature leaf drop is observed, starting from the lower levels. The plant stops growing, and buds may fail to form or wither before opening.

The pathogen responsible for the disease is the fungus Stagonosporopsis ajacis (a synonym for Ascochyta aquilegiae), which belongs to the class of fungi imperfecti.

The pathogen persists as pycnidia and mycelium on plant debris, fallen leaves, and in the soil around the infected plant, overwintering in a dormant state.

The spread of the fungus during the growing season occurs through spores (pycnidiospores) carried by rain splashes, dew, as well as by insects and wind.

The biology of the pathogen is specifically adapted to plant species in the Ranunculaceae family, making Delphiniums particularly susceptible to this type of fungal infection.

Primary infection usually occurs in spring when spores land on young leaves under favorable weather conditions, penetrating through the stomata or micro-injuries in the tissue.

High air and soil humidity, especially during prolonged rainy periods, create ideal conditions for the germination of fungal spores and the development of Ascochyta blight.

The optimal temperature for the active growth of the pathogen's mycelium ranges from +18 to +25 degrees Celsius, with high humidity acting as a critical facilitating factor.

Dense planting of Delphinium, which obstructs proper air circulation and delays the drying of leaves after watering or precipitation, promotes the rapid spread of the disease.

Weakening of plants due to nutrient deficiencies or pest attacks significantly increases the risk of infection in temperate climates.

Overhead watering in the evening increases the risk of infection because moisture remains on the leaves throughout the night, providing the fungus with ample time to penetrate the tissues.

The main damage lies in the loss of the plant's decorative appearance, as the spotting affects a significant portion of the leaf surface, making the flower look unattractive.

Severe infestation leads to a sharp decrease in photosynthesis, causing the plant to lose vital energy and preventing the formation of healthy flower spikes.

In cases of early infection in young specimens, total death of the plant or critical stunting is possible, making it impossible to grow the crop successfully under these conditions.

Infected plants become a source of infection for neighboring healthy specimens, which, without protective measures, can lead to the total loss of a Delphinium collection.

The accumulation of the pathogen in the soil makes it impossible to grow susceptible crops in the same area for several seasons without conducting thorough disinfection.

The primary measure is the thorough removal and burning of all plant debris in the fall, as this is where the main source of the infection overwinters.

It is necessary to strictly follow cultivation techniques: ensure optimal spacing between plants to improve ventilation and reduce humidity in the root zone.

To prevent the spread of the disease, it is recommended to use systemic and contact fungicides containing copper or modern azole compounds.

Preventive treatments of Delphiniums with biological preparations based on Bacillus subtilis help strengthen the plant's immunity and create a protective barrier.

• Water exclusively at the base, avoiding getting water on the leaves.
• Regularly remove the lower yellowing leaves to reduce the source of infection.
• Practice crop rotation, replanting Delphinium in a new location every 3-4 years.