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Ministry of Agriculture, Food and Rural Affairs

Moldy core

Moldy core
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Beginner

Scientific Names
Moldy core is a disease caused by many different species of fungi that naturally occur in the orchard.

Identification

  • The core of the infected apples has a thick brownish yellow mold,
  • Seeds are often rimmed with white mold,
  • Fruit may ripen and drop prematurely.

Often Confused With

  • Black rot - Black rot can be distinguished late in the season or in storage by the appearance of tiny pimple like black pycnidia on the rotted fruit. Moldy core is not evident until the apple is cut open showing thick yellow mold and seeds rimmed with white mold.

Period of Activity
Moldy core is more of a problem during years with light fruit set or in years when dry weather in early summer is followed by heavy rains in late summer. Wet weather during bloom also creates conditions favorable for the fungi to produce spores.

Scouting Notes
Symptoms of the disease include premature ripening and premature drop. It can be difficult to detect moldy core without slicing the fruit in half and looking for mold growing in the seed cavity.

Thresholds
None established.

Advanced

Scientific Names
Moldy core is a disease caused by many different species of fungi that naturally occur in the orchard.

Identification
The core of the infected apples has a thick brownish yellow mold. Seeds are often rimmed with white mold. Fruit may ripen and drop prematurely.

Often Confused With

  • Black rot - Black rot can be distinguished late in the season or in storage by the appearance of tiny pimple like black pycnidia on the rotted fruit. Moldy core is not evident until the apple is cut open showing thick yellow mold and seeds rimmed with white mold.

Biology
The fungi that cause this disease colonize the flower parts as soon as the blossoms open, entering the developing fruit through an opening in the calyx. Fruit are infected when the spores from these fungi move into the core of the fruit through the calyx. Varieties that generally have an open calyx such as Red Delicious are more susceptible to moldy core.

Warm weather and humidity favour moldy core development and environmental conditions that prevent the calyx from closing during fruit development provide an opportunity for spores to infect the fruit. Once a moldy core fungus infects the core of the apple, fungicide programs are unable to eliminate the disease.

Period of Activity
Moldy core is more of a problem during years with light fruit set or in years when dry weather in early summer is followed by heavy rains in late summer. Wet weather during bloom also creates conditions favorable for the fungi to produce spores.

Scouting Notes
Symptoms of the disease include premature ripening and premature drop. It can be difficult to detect moldy core without slicing the fruit in half and looking for mold growing in the seed cavity.

Thresholds
None established.

Management Notes

  • Moldy core penetrates the flesh during long-term storage and causes rot, so it is wise to market fruit that is suspected to have moldy core as soon as possible.
  • Once in an orchard, moldy core does not spread and its presence does not give an indication of future problems.
  • Apple cultivars vary in their susceptibility to moldy core. Avoid cultivars with open calyxes (Delicious and Ida Red) in areas prone to moldy core problems.
  • Although some studies have found fungicides used during bloom help to reduce moldy core, results are erratic and fungicides are rarely recommended.
  • Cultural practices to open the tree canopy and encourage airflow and light penetration (tree training and pruning) help promote fast drying of plant surfaces, and reduce the incidence of moldy core.