Heat management was certainly a challenge this growing season with prolonged periods of +90°F temperatures and drought conditions throughout Wisconsin. These conditions, high heat and low humidity, create the ideal environment for scald on the fruits. To combat these conditions and cool the cranberries many relied on irrigation during these hot and dry periods. Irrigation requires a steady balance between optimizing marsh conditions and not oversaturating the field which in turn can create conditions conducive to fungal diseases.

Typically, sunscald is observed on fruits in the upper canopy that are exposed to sunlight. Scald manifests as a physiological breakdown during the fruit stage of development and appears as circular or oval-shaped lesions on the fruit surface (Figure 1). Recently planted beds and beds with sparse growth are especially susceptible to sunscald. Fungicide applications following sun scalding events are not recommended. Scald severity can differ based on the intensity of sun exposure, canopy temperatures, soil temperatures, and changes in wet or dry conditions. Once sunscald has occurred, berries and vines become more susceptible to other injuries and pathogens. Minimizing stress on the vines now until harvest will help reduce the impact of berry damage.

Symptoms of fruit rot have become visible in marshes across the state. Infections that cause fruit rot occur during bloom and early fruit set, and fungicide applications are targeted during these critical periods to prevent infections. Some infections are latent (or asymptomatic) in the plants. Fungicide applications later in the season do not improve disease control, as rot that occurs later in the season is most likely from early-season infections that remained dormant until fruit ripening. To reduce the impact of established fruit rot infections and minimize the risk of fruit rot issues post-harvest (ex. storage rots like black rot) there are several cultural practices that can be utilized:

• Manage canopy density: Very dense canopies can create a microclimate conducive to fungal infection. Over-fertilization can lead to heavy vine growth which can worsen fruit rot infections.
• Manage water: During harvest, minimize exposure time of the fruit to water to reduce disease incidence, this is especially crucial for storage rot.
• Minimize damage to the fruit: Wounded fruit provides an entry point for fungal pathogens.
• Storage temperatures below 5°C (41°F) are recommended to minimize fruit decay.
• Storage of fruit for processing at temperatures slightly above 0°C (32°F) can reduce the incidence of black rot.
• Removal of plant debris that accumulates around the perimeter of beds during harvest will help reduce fungal inoculum.

This article was posted in Cranberry, Disease and tagged Cranberries, disease, Fruit Rot, Leslie Holland, sunscald.