Alternaria blight of figwort

The first signs of infection appear as small brown or dark-grey spots that emerge on the leaves of figwort at the beginning of the growing season.

As the disease progresses, these spots expand and develop a zonal appearance, which is typical for many Alternaria species. Often, a light or chlorotic halo surrounds the necrotic tissue.

Under high humidity, a velvety dark-brown to olive-colored layer of fungal sporulation can be observed on the underside of infected leaves.

Severe infection leads to premature yellowing, withering, and leaf drop, which significantly damages the aesthetic value of the plant and weakens its overall vigor.

In advanced cases, the necrosis spreads to stems, causing deformation, cracks, and the potential death of individual shoots if the stem is girdled.

The causal agent of this disease is the fungus Alternaria scrophulariae, which is a member of the widespread Alternaria genus. This pathogen is known for its high specificity to plants in the Scrophulariaceae family.

The fungus survives in the form of mycelium or conidia on crop debris, in the soil, or on infected seed material. It is characterized by high adaptability to various environmental conditions.

Disease spread is primarily achieved through airborne conidia or by water splashes during rain or irrigation. It can easily move between plants when environmental conditions are conducive.

The fungus possesses a saprophytic phase, allowing it to persist on dead tissues for extended periods until suitable conditions for active parasitism occur.

Rapid spore production takes place under high humidity, which contributes to the fast buildup of infection pressure in gardens or fields.

Infection thrives in conditions of high humidity (above 75%) and moderate temperatures ranging from +18°C to +25°C.

Prolonged rainfall, heavy dew, and improper irrigation that allows for moisture retention on leaf surfaces are the primary drivers of disease spread.

Overcrowded plantings reduce air circulation and increase local humidity levels, which significantly accelerates spore germination and entry into plant tissues.

Plants suffering from nutrient deficiencies or other abiotic stresses show lower resistance, making them more susceptible to infection by Alternaria scrophulariae.

Excessive nitrogen fertilization promotes the growth of soft, lush tissues that are much more vulnerable to penetration by fungal hyphae.

The main impact is the loss of decorative quality, which is crucial for plants used in landscaping and ornamental gardening.

Disruption of photosynthesis due to extensive leaf damage leads to general plant stunting, reduced flowering, and a slower overall growth rate.

Premature leaf senescence leaves the plant vulnerable to winter conditions, frequently leading to reduced frost tolerance and potential plant death.

In nursery settings, the infection can spread quickly, affecting the quality of planting material and leading to significant economic losses for producers.

The persistence of the fungus in the soil makes it difficult to cultivate sensitive species in the same location without thorough sanitation or rotation.

Prevention starts with providing sufficient spacing between plants to ensure proper aeration and prevent moisture buildup in the canopy.

Regular sanitation, including the removal and disposal of infected plant debris, is mandatory to reduce the primary inoculum source for the next season.

Avoiding overhead irrigation is highly recommended; preference should be given to drip irrigation to keep leaf surfaces dry.

Chemical control involves the use of systemic and contact fungicides known to be effective against Alternaria species, applied during periods of high risk.

• Prompt removal of diseased foliage.
• Practice crop rotation.
• Use healthy and certified planting material.
• Preventative fungicide applications.
• Optimization of mineral nutrition to boost plant immunity.