Cercospora leaf spot of cress

The main signs of the disease are circular or angular spots on the leaf blades. At the beginning of development, they have a light gray or brownish hue, gradually acquiring a dark border.

In conditions of high humidity, a grayish or olive coating consisting of the fungus's conidia and conidiophores forms on the surface of the spots on the underside of the leaf.

As the disease progresses, the spots increase in size and can merge with each other, covering significant areas of the leaf. This leads to premature yellowing and necrosis of the leaf blade.

When young plants are infected, the disease can cause petiole distortion and stunted growth of the crop. The infected plant becomes suppressed, making it unsuitable for market sale.

A characteristic diagnostic feature is the necrosis of tissues in the center of the spot, which sometimes leads to the fallout of the dead areas, giving the leaf a perforated appearance.

The causative agent of the disease is the imperfect fungus Cercospora nasturtii, which belongs to the class of hyphomycetes. The pathogen infects plant tissues by entering through stomata or mechanical injuries to the epidermis.

The mycelium of the fungus develops within the intercellular spaces of the infected tissue, gradually destroying the leaf structure. Conidiophores with conidia form in the infected spots, which are dispersed by wind, raindrops, and insects to healthy plants.

This microorganism survives in the soil on plant debris and can also be transmitted via infected seeds. The infectious background accumulates due to poor crop rotation and continuous cropping of cruciferous plants.

The life cycle of the pathogen is closely tied to environmental humidity. Under optimal conditions, the fungus is capable of producing several generations of spores within a single salad growing season.

The biology of Cercospora nasturtii has been studied as a specialized parasite that primarily affects plants of the Brassicaceae family, including watercress and other types of cress.

The development of the disease is favored by warm weather with air temperatures ranging from +20°C to +28°C. These conditions are most favorable for the active germination of conidia.

High relative humidity, frequent fogs, or heavy dews trigger the massive spread of the infection across plantations. In greenhouses, the disease progresses faster due to poor air circulation.

Dense plantings that hinder aeration create a microclimate with high humidity levels, which is a critical factor for the initiation of a Cercospora epiphytotic.

Insufficient watering or conversely waterlogged soil, which weakens plant immunity, makes them more susceptible to the penetration of Cercospora nasturtii spores.

Prolonged periods of rain contribute to the rapid spread of zoospores from infected areas to neighboring healthy plants, covering the entire field.

The harmfulness of the disease lies in the significant reduction of the commercial quality of cress. Infected leaves quickly lose their marketability and become unsuitable for consumption.

With intensive infection, the rate of photosynthesis decreases, leading to stunted plant growth and a reduction in the total biomass of the harvest.

In case of early infection, the loss of young seedlings is possible, leading to thinning of the crop and the need for reseeding over large areas.

Cercospora promotes premature aging of plants, which reduces the shelf life of the harvested greens. Affected produce is prone to secondary infection by soft rot bacteria.

Economic losses include both direct losses from reduced marketable yield and additional costs for fungicide treatments and unplanned agronomic interventions.

The most important preventive measure is compliance with crop rotation. It is not recommended to grow cress on the same plot more often than once every 3–4 years, avoiding predecessors from the cabbage family.

Deep plowing of the soil after harvest is necessary to destroy plant debris where the fungal mycelium overwinters.

The use of only healthy, pathogen-free seeds is the key to preventing primary infection of the crops.

Regulating the microclimate in greenhouses through regular ventilation helps maintain humidity at a level unfavorable for the development of Cercospora nasturtii.

• Application of fungicides at the first sign of disease according to regulations.
• Elimination of weeds that can act as infection reservoirs.
• Timely removal and disposal of infected plants.
• Application of balanced fertilizers to strengthen plant immunity.