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Ministry of Agriculture, Food and Rural Affairs

Calyx End Rot & Dry end Rot

Calyx end rot on fruit caused by S. sclerotiorum usually observed early in the season Dry eye rot caused by B. cinerea is more often observed on large fruit later in the growing season
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Beginner

Scientific Names
Sclerotinia sclerotiorum (calyx end rot), Botrytis cinerea (dry end rot)

Identification

  • Symptoms first appear on fruit as a reddish discolouration turn into small (1-2 cm) water-soaked lesions on the calyx of the fruit.
  • Lesions develop into light brown dry rot that may penetrate several millimeters into the apple tissue.
  • The rot is soft initially, but eventually dries out to a tan brown, and is slightly sunken with a red border.
  • A shallow, dry or corky rot generally develops in the flesh beneath the spot.
  • Calyx end rot lesions tend to form on one side of the calyx.
  • Dry eye rot lesions are centred around the calyx.
  • Symptoms are usually confined to the calyx end and are not associated with extensive internal rotting of the fruit.
  • Infected fruit often drop prematurely.
  • Fruit infected with dry eye rot often develop gray mold in storage.

Often Confused With

  • Calyx end rot and black rot on the fruit - Calyx end rot is light brown dry lesion, slightly sunken with a red border.  Black rot symptoms at the calyx end have concentric dark and light rings and tiny pimple-like black pycnidia may be visible.
  • Dry end rot and apple scab on the fruit - Dry end rot is light brown dry lesion, slightly sunken with a red border. Apple scab is a brown to black corky lesion that may be cracked. Apple scab may be found at the calyx end of the fruit but lesions can also be found on the entire fruit surface.

Period of Activity
Infections usually occur during bloom or shortly after, although frequently symptoms are not visible until several weeks later. Rot symptoms usually become visible about one month after petal fall. Dry eye rot often develops later in the season (late July to early August) than calyx end rot which is often observed early to mid summer.

Scouting Notes
During weekly pest monitoring examine fruit for the presence of lesions.

Thresholds
None established.

Advanced

Calyx end rot and dry end rot are two diseases of apple often confused with each other. Both diseases infect the fruit and cause rot to form at the calyx end of the apple. Calyx end rot is caused by the white mold fungus, Sclerotinia sclerotiorum, and dry end rot is caused by the gray mold fungus, Botrytis cinerea.

Scientific Names
Sclerotinia sclerotiorum (calyx end rot), Botrytis cinerea (dry end rot)

Identification
Symptoms first appear as a reddish discolouration and turn into small (1-2 cm) water-soaked lesions on the calyx of the fruit. Lesions develop into light brown dry rot that may penetrate several millimeters into the apple tissue. The rot is soft initially, but eventually dries out to a tan brown, and is slightly sunken with a red border. A shallow, dry or corky rot generally develops in the flesh beneath the spot. Generally calyx end rot lesions tend to form on one side of the calyx, while dry eye rot lesions are centred around the calyx. The two diseases look very similar and the isolation of the pathogen is necessary for positive identification.

These diseases are more common in seasons of prolonged cool, wet weather during bloom and petal fall. Once the fruit is infected, the disease does not spread to other fruit during the rest of the growing season. The susceptibility of apple cultivars to calyx end rot and dry eye rot is not known, but both diseases have been observed in McIntosh, Cortland, Paulared, Rome Beauty Delicious, Honeycrisp, Milton and Macoun. Symptoms are usually confined to the calyx end and are not associated with extensive internal rotting of the fruit. Up to 20% of fruit are infected in some blocks. Rot symptoms usually become visible about one month after petal fall. Infected fruit often drop prematurely. Fruit infected with dry eye rot often develop gray mold in storage.

Often Confused With

  • Calyx end rot and black rot on the fruit - Calyx end rot is light brown dry lesion, slightly sunken with a red border.  Black rot symptoms at the calyx end have concentric dark and light rings and tiny pimple-like black pycnidia may be visible.
  • Dry end rot and apple scab on the fruit - Dry end rot is light brown dry lesion, slightly sunken with a red border. Apple scab is a brown to black corky lesion that may be cracked. Apple scab may be found at the calyx end of the fruit but lesions can also be found on the entire fruit surface.

Biology
Infections usually occur during bloom or at petal fall. Rot symptoms usually become visible about one month after petal fall. There is a very narrow window for infection and disease development caused by S. sclerotiorum. The pathogen infects and causes disease in more than 360 species of plants including many common weeds. The pathogen overwinters as hard, black sclerotia just under the soil surface usually around the base of infected weeds. In the spring, when soil moisture remains near field capacity for 10 days to several weeks and temperatures remain cool (11-20ºC), sclerotia germinate and produce tiny light brown mushrooms called apothecia. The apothecia have inverted cup-like caps that contain ascospores, which are forcibly ejected into the environment. These spores do not infect fruit directly but rather infect senescent, withered tissues such as sepals or flower petals during petal fall. The sepals or petals are colonized by the fungus, and the pathogen eventually invades the calyx end of the fruit. There is very little potential for further infection to occur after petal fall, since S. sclerotiorum does not produce secondary spores and does not spread from infected apple to non-infected apple during the growing season. Once inside the calyx end, the fungus eventually colonizes the adjacent fruit tissue causing the rot symptoms observed. Infected fruit usually drop prematurely and the fungus infects susceptible weeds it directly contacts on the orchard floor. Eventually sclerotia are formed either on the colonized fruit or infected weeds. The dry eye rot pathogen (B. cinerea) also overwinters as sclerotia, usually in infected apples left on the orchard floor from the previous season. In the spring, sclerotia produce spores that infect the sepals or petals during bloom. The fungus remains quiescent until fruit begin to mature later in the summer.

Period of Activity
Infections occur during bloom to petal fall. Symptoms of dry eye rot often develops later in the season (late July to early August) than calyx end rot which is often observed early to mid summer.

Scouting Notes
Regular scouting is the best way to assess disease levels. During weekly pest monitoring examine fruit for the presence of lesions.

Thresholds
None established.

Management Notes

  • Effective weed management helps reduce populations of the white mold fungus.
  • Mowing the orchard floor, particularly in orchards with a history of calyx end rot, to keep vegetation short during the 10-14 days leading up to petal fall, allows soil to dry and reduce the environmental conditions required for sclerotia germination and consequent spore production.
  • Picking and removing infected fruit from the orchard after harvest also helps reduce inoculum from building up in the orchard.
  • Since these pests are sporadic, special sprays are not required and practices employed to manage other diseases provide subsequent control of these pests.
  • The use of some early season fungicides (see OMAFRA Publication 360, Guide to Fruit Production) provides subsequent control of the disease.