Hawthorn monilinia

The life cycle of this pathogen depends on overwintering structures, primarily mummified fruits that remain on the branches or fall into the soil litter.

In spring, apothecia develop from the overwintered sclerotia. These structures release ascospores, which are the primary inoculum spreading by wind during the flowering stage.

The fungus infects the plant through the stigmas of the flowers, quickly colonizing the ovaries. Secondary spread is facilitated by conidia dispersed by insects and rain splash.

Monilinia johnsonii is unique due to its host specificity, meaning it is specifically adapted to cause blossom and fruit rot in hawthorn trees.

The first signs of the infection appear shortly after the flowering period. The ovaries begin to blacken, wilt, and die, often remaining attached to the branches.

Over time, the affected fruits shrink and turn into hard, black, wrinkled mummies. This distinct blackening is a characteristic feature of this specific monilinia species.

Under humid conditions, a greyish or brownish conidial mass may emerge on the surface of the infected fruits or flower stalks.

While the main symptoms occur on reproductive organs, leaves and young shoots may occasionally show brown lesions as the mycelium spreads locally.

Internal tissues of the fruit lose their integrity, become soft, and turn dark brown or black, rendering them completely useless for any purpose.

Cool and rainy weather during the flowering season is the most significant factor promoting the development of hawthorn monilinia.

High relative humidity is essential for the ascospores to germinate on the flower stigmas, leading to successful infection of the fruit embryo.

Dense canopies and poor air circulation within the orchard create favorable conditions for the fungus to spread rapidly from tree to tree.

The presence of mummified fruits from previous seasons serves as a persistent reservoir, ensuring the disease returns annually if not managed.

Temperatures ranging from 15°C to 22°C are optimal for the growth of the fungus, which often coincides with the hawthorn's natural blooming window.

The primary economic impact is the massive loss of fruit yield. Since the infection hits during the flowering stage, the entire crop can be destroyed.

The disease causes significant stress to the hawthorn tree, potentially weakening it against secondary pests and environmental stressors over multiple years.

Infected berries are contaminated with fungal metabolites and cannot be used for medicinal or culinary purposes, representing a complete loss for growers.

If not controlled, the pathogen builds up in the orchard, turning the area into a hotspot for annual outbreaks that are difficult to eradicate.

For ornamental hawthorns, the disease ruins the aesthetic value of the trees due to the persistent black mummified fruits hanging on the branches.

Sanitation is the most critical control measure. Growers should collect and destroy all mummified fruits and prune away infected branches during the dormant season.

Pruning to open the canopy improves airflow and light penetration, which helps to reduce the humidity levels that favor fungal growth.

Fungicide applications are recommended, specifically targeting the blooming period to protect the flowers from initial ascospore infection.

Copper-based products are often used for preventive dormant or early spring sprays to reduce the overall fungal spore load in the orchard.

• Remove and burn all mummified berries.
• Apply fungicides at the start of flowering.
• Promote air circulation through strategic pruning.
• Monitor for insect pests that may injure fruit.
• Apply protective sprays during wet spring seasons.