Rust of mock strawberry

The primary symptom of this infection is the appearance of characteristic pustules typical for rust fungi. These small, circular structures develop on the underside of the leaf and eventually rupture the epidermis.

The color of these pustules ranges from yellow to brownish-orange, caused by the mass production of fungal spores. As the infection progresses, the leaves become chlorotic, yellow, and may wither prematurely.

In severe cases, the fungus affects not only the leaves but also the petioles, causing small swellings and deformations. This disrupts the overall plant vigor and hinders normal metabolic functions.

Visual inspection during mid-season reveals the presence of spore powder on the lower leaf surface, which is the most reliable indicator of an ongoing infection. Early detection is vital for containment.

In the final stages, the affected leaf areas undergo necrosis, resulting in brown dry spots of varying shapes. The plant loses its aesthetic value and significantly lags behind healthy specimens in growth.

The pathogen responsible for this disease is Frommeëlla duchesneae, a fungus belonging to the order Pucciniales. It is an obligate parasite, meaning it requires living host tissue to survive.

The fungus has a complex life cycle with several spore-producing stages, which allow it to persist under various environmental conditions. It penetrates the host via stomata or direct epidermis entry under humid conditions.

This pathogen is highly specialized, primarily infecting plants of the genus Duchesnea, especially Duchesnea indica. This specificity makes it a significant threat to mock strawberry plantations.

Spores are dispersed primarily by wind currents, rain splashes, or improper irrigation practices. Given the right environment, the fungus can colonize new areas very rapidly.

The fungal mycelium spreads within the intercellular spaces of the plant, drawing nutrients directly from the host cells. This constant drain weakens the plant, reducing its winter hardiness and resilience.

The development of the disease is highly dependent on air humidity and temperature. Prolonged rainfall, heavy morning dew, and fog during the growing season create the perfect environment for outbreaks.

Temperatures ranging between +18 and +24 degrees Celsius are considered optimal for spore germination and infection. While dry and hot weather slows down the pathogen, it does not fully eradicate the spores.

Overcrowded plantings create a microclimate with poor air circulation, allowing moisture to persist on the leaves for longer periods. These conditions are conducive to rapid fungal spread and potential epiphytotics.

Surface moisture on leaves is a critical requirement for successful infection. Therefore, overhead irrigation, especially in the evening, significantly increases the risk of spreading the rust pathogen.

Infection cycles are also supported by plant debris left on the site, where the fungus can survive during off-seasons. Springtime humidity then triggers the release of spores from these wintering sites.

The main impact of Frommeëlla duchesneae is the disruption of photosynthesis due to extensive leaf damage. The plant loses a substantial part of its energy-producing surface area.

Reduced photosynthetic efficiency weakens the plant, negatively impacting its vegetative propagation. Heavily infected clusters struggle to spread and lose their density and overall plant vigor.

Continuous infection over several seasons leads to total loss of decorative appeal, making the plant unsuitable for its intended use in landscape design and ground cover applications.

Damaged tissues become more susceptible to secondary pathogens, including various rots and opportunistic bacterial infections, leading to a complex decline in plant health.

Exhaustion of nutrient reserves makes the plant less prepared for winter, leading to higher rates of winterkill during temperature fluctuations. This can cause permanent loss of the plantation.

Prevention starts with site selection: choose well-lit areas with good airflow. Avoid overcrowding and maintain proper spacing to ensure that leaves dry quickly after rainfall or dew.

Sanitation is a crucial control measure. Remove and destroy all infected plant debris at the end of the season to minimize the carry-over of spores for the next year.

Implement proper irrigation techniques, specifically root-zone watering. Avoid wetting the foliage to prevent creating the moist environment necessary for spore germination and infection.

If symptoms appear, systemic fungicides from the triazole or strobilurin classes can be used. Applications should be repeated every 10–14 days, following label instructions precisely.

Biological fungicides based on Bacillus subtilis can be effective for early-stage control or as a preventative measure. Regular scouting throughout the season allows for timely intervention.