Sclerotinia oxycocci

The life cycle of this fungus is highly synchronized with the growth stages of cranberry plants. It overwinters as sclerotia inside mummified berries left on the bog surface.

In spring, as buds begin to break, these sclerotia germinate to produce apothecia, which release ascospores that are dispersed by wind or water splashes to young shoots and flowers.

The fungus thrives in cool, wet environments, which are characteristic of cranberry growing regions, especially during the critical periods of shoot elongation.

Because the pathogen specifically targets reproductive organs, it is considered a major limiting factor in high-yield commercial cranberry production.

The pathogen specifically infects plants of the genus Vaccinium, primarily Vaccinium macrocarpon (American cranberry) and Vaccinium oxycoccos.

The disease impacts both vegetative and reproductive phases, leading to "tip blight" on succulent shoots and severe fruit rot as the season progresses.

Infected berries become hard, lose their commercial value, and contain fungal tissues that can contaminate the entire harvest batch if not properly managed.

Significant economic losses occur when environmental conditions favour the pathogen, resulting in widespread fruit mummification throughout the plantation.

Left unchecked, the inoculum load within the bog increases annually, making it progressively more difficult to produce high-quality, disease-free berries.

The first symptom is the sudden wilting and drooping of new vegetative tips, which often display a greyish fungal mycelium under humid conditions.

During the flowering stage, infected blossoms will wither prematurely and turn brown, indicating that the fungus has successfully colonized the floral parts.

Affected fruits are characterized by a firm, hard texture and premature discoloration, often appearing lighter or prematurely red before drying out.

A mature sclerotium, which is a dense mass of black fungal tissue, eventually fills the inside of the mummified berry, allowing the fungus to survive winter.

During spring, small, tan-coloured, mushroom-like apothecia can be observed emerging from the remnants of last year's infected berries in the mulch layer.

Effective management of Sclerotinia oxycocci involves a rigorous combination of cultural sanitation and targeted fungicide applications.

Sanitation is paramount: removing crop residues and ensuring complete harvesting of berries are critical steps to reduce the overwintering inoculum.

Applying a thin layer of sand (sanding) over the cranberry beds helps to bury the sclerotia, creating a physical barrier that prevents ascospores from reaching the host plants.

Chemical control focuses on protecting blossoms during the bloom period, when the plant is most vulnerable to infection by airborne ascospores.

• Regular monitoring for signs of apothecia emergence in early spring.
• Strategic timing of fungicide sprays according to the flowering phenology.
• Maintaining optimal irrigation to reduce stagnant water that favours disease spread.