Pear (Pyrus spp.)-Storage Rots

See:

Apple (Malus spp.) - Storage Problems

Cause There are many storage disorders caused by abiotic problems beyond Bartlett Decay described below. Many of these are covered in a separate section on Apple-Storage Problems.

Bartlett Decay-If the water is warm (caused by running fruit picked on a hot day) or the SOPP concentration is too high, or the rinse is inadequate, burning at the lenticels can result.

Most of this section will cover storage rots caused by fungal pathogens. The most common fungal decay problems in OR and WA packing houses are blue and gray mold.

Blue and Gray mold-The two major postharvest rots of pear and apple are blue and gray mold caused by Penicillium spp. and Botrytis cinerea, respectively. Blue mold infections occur mainly through wounds that occur prior to storage. The fungus penetrates through these wounds, bruises, and lenticels on overripe fruit in storage. Delays in cooling fruit after harvest can increase risk of this rot. High nitrogen levels and tree vigor also contribute to disease development. Gray mold survives on organic matter and fruit left in the orchard. This fungus infects fruit any time before harvest starting at full bloom.

Bull's-eye rot is frequently caused by the fungi Neofabraea perennans and N. vagabunda (formerly Neofabraea alba) in the Pacific Northwest. Neofabraea kienholzii and N. malicorticus can also occur on apple. Infections occur in the orchard from cankers caused by the pathogen in the previous season. Infections can occur between bloom and harvest, but susceptibility increases as the growing season progresses. Rain or overhead tree irrigation during the growing season can increase risks of inoculum spread and rot development. 'Bosc' is amongst the highly susceptible cultivars.

Alternaria rot- Several Alternaria spp. can infect fruit in the orchard through skin breaks or areas weakened by sunburn or bruising. Areas with predominantly Bosc and Bartlett pear should consider Alternaria rot as one of the main post-harvest disease problems while areas where Anjou and Comice pears are predominant, this may be of minor economic importance. Although symtoms develop in storage, inoculum for Alternaria rot comes from the orchard. It is recommended to apply preventative sprays during the growing season, especially at petal fall and close to harvest.

Phacidiopycnis rot-Phacidiopycnis piri has been found in all major pear-producing areas of the Pacific Northwest, however, its importance is not well known and can vary from one year to another. It is associated with dead bark, cankers, and twig dieback of pear trees. Spores from pycnidia are the main type of inoculum in the orchard. Infection of fruit occurs in the orchard between bloom and harvest but symptoms develop in storage. Preventing infections close to harvest is recommended. Resistance to group 7 and 9 fungicides has increased from 2005 to 2017. Note that the pathogen found on apples is P. washingtonensis and called speck rot.

Sphaeropsis rot-Sphaeropsis pyriputrescens infects fruit in the orchard but symptoms develop postharvest on 'd'Anjou' pear and several apple cultivars. Although found at low frequencies, the disease is relatively widespread throughout central Washington but not reported yet in Oregon. The fungus can cause twig dieback and can survive on dead fruit spurs and mummified fruit on apple trees and crabapple pollenizers such as Manchurian.

Mucor rot-Mucor piriformis spores survive in the soil in organic matter and are transported to storage rooms on bins left in the orchard for several days. Cross-contamination can occur when fruit are drenched in flume water. Infections occur mainly through wounds.

Cladosporium rot-Cladosporium herbarum.

Storage scab-Venturia pyrina.

Sprinkler rot-Phytophthora cactorum is spread through irrigation water in orchards and can become problematic under continuous wet conditions during harvest that are not common in the Pacific Northwest.

Coprinus rot-Coprinopsis psychromorbida (formerly Coprinus psychromorbidus) . A rare problem that is more a problem on pear than apple. Not found during a WA survey from 2016 to 2018.

Side rot-Cadophora malorum (formerly Phialophora malorum). This minor rot has been reported in Oregon and elsewhere on 'Bosc' as well as on other cultivars in Europe. Similar disease symptoms yielded Diaporthe rudis in 2017-2018 in southern Oregon.

Phacidium rot-Phacidium lacerum was found causing storage rot on apple and pear in Washington. Gala and Honeycrisp were the most susceptible while Cosmic Crisp was the least. Symptoms occurred on fruit inoculated in the field after 3-months cold storage. Resistance to group 7 and 9 fungicides has increased from 2005 to 2017.

Symptoms

Blue mold-Light brown to tan lesions that eventually become soft, watery, and covered with large numbers of green then blue spores. Lesions are at first sunken but continue to collapse the fruit. The decay has a musty odor and separates from the healthy tissue if pressure is applied.

Gray mold- Lesions are light brown to brown, sometimes translucent, with a diffuse margin. Rotted tissue is less soft than blue mold and is not easily separated from healthy tissue. Infections are spongy in consistency and become covered with fuzzy gray mycelium, which can eventually produce copious amounts of spores. The disease can spread from diseased to healthy fruits forming nest-like pockets of rotted fruit.

Bulls'-eye rot-spots with light-brown sunken centers and a dark-brown halo. The rot has a firm and mealy texture. Rot does not spread from one fruit to another.

Alternaria rot - Infection by Alternaria spp. result in dry rot symptoms where the lesions are brown to dark brown depending on a cultivar. Water-soaked margins are visible between infected and healthy tissues in cultivars such as Bartlett and Bosc. At the site of infection, olive green to black mycelium with few spores are often visible under high moisture conditions.

Phacidiopycnis rot-Rot may develop at the calyx- or stem-end and is rarely associated with wounds. Decayed areas appear water-soaked in the early stages and turn black as the rot develops but the margin remains water-soaked. Decayed fruit eventually look like a ripe avocado. The disease may be confused with gray mold but has a firmer consistency and a translucent margin compared to a brownish margin for gray mold.

Sphaeropsis rot-a firm, brown rot develops from the calyx- or stem-end. The fungus may form pycnidia on the decayed lesions as the rot advances. Decay develops along the vascular tissue and causes the flesh to become brown. Sphaeropsis rot can be distinguished from gray mold by its strong odor. Generally develops after 2 months in storage.

Cladosporium rot-dark brown to black, circular, water-soaked spots. Can be confused with side rot.

Mucor rot- Lesions are light brown and separate from the healthy tissue if pressure is applied and thus in early stages may be confused with blue mold. Later there is the production of coarse white fungal strands with black spore heads (sporangia).

Storage scab-small, light brown, sunken spots.

Sprinkler rot-lesions are light brown and soft with a pungent, phenolic odor.

Fire blight-lesions are dark brown and hard.

Coprinus rot-large depressed spots with light-brown centers and a thinner, dark-brown margin. Decayed tissue is firm and dry. A white cobweb-like growth on the surface can cause a nest or cluster of rotted fruit. At its early stage, the disease can be mistaken for bulls'-eye rot.

Side rot-dark spots indistinguishable from Cladosporium rot.

Phacidium rot-A stem-end rot, calyx-end rot and wound-associated rot. Lesions are light brown and decayed tissue is spongy to firm. The fungus also can cause cankers on twigs.

Cultural control A combination of techniques will aid in overall control.

• Avoid use of over-tree evaporative cooling or use it in such a way that fruit is not wet for extended periods of time.
• Use low-angle sprinkler nozzles.
• Maintain good in-row weed control; mow grass between rows.
• Use foliar nutrient sprays before harvest. Calcium-based products may help reduce the impact of some diseases. Nutraphos-24 applied at 15 lb/A 3 weeks before harvest reduced blue mold in 'Anjou' pears by 50%. Summer applications of calcium chloride, three (3) times 2 weeks apart, help reduce both blue mold and side rot.
• Use a minimal amount of nitrogen fertilizer.
• Harvest at proper maturity, and instruct harvesters on the proper technique for removing fruit from the tree. Late harvest can result in increased decay rates.
• Clean fruit bins before filling, and keep soil off the bottom. A hot water pressure wash or steaming can help clean bins. Plastic bins are better than wooden bins. Clean storage rooms of all debris well before filling and treat surfaces with a disinfectant.
• Harvest and cool fruit quickly. Keep bins out of sun.
• Avoid or minimize injuries at harvest and during handling by smoothing orchard roads and driving slowly. Paying pickers by the hour rather than by the bin has resulted in fewer stem punctures and fruit injuries.
• Controlled-atmosphere storage, especially with low (1%) oxygen, reduces the incidence and severity of some rots.
• Do not return cull fruit back into the orchard.

Chemical control Use a combination of pre and postharvest fungicides. Fruits should be thermo-nebulized (fog or aerosol) or drenched with fungicides shortly after harvest to minimize postharvest rots. Rotate fungicides from different FRAC groups to avoid using the same fungicide twice on the same fruit from pre- to post-harvest. Resistance to several fungicides has been detected.

• Fungicides applied during the growing season, especially before heavy rains preharvest. Use fungicides from different FRAC groups that might be used post-harvest. Resistance to several fungicides has been detected in stored fruit. The fungus also can cause cankers on twigs.
  • Cinnerate at 32 to 64 oz/100 gal water plus an adjuvant. Was effective on apple 7 days PHI in two eastern WA tests. No reentry indicated. O
  • Inspire Super at 12 fl oz/A. Do not apply within 14 days of harvest. Group 3 + 9 fungicide. 12-hr reentry.
  • Merivon at 4 to 5.5 fl oz/A is labeled for blue and gray mold. Do not use with EC or oil-based products. May be used day of harvest. (Consider other products if it was used in the orchard for disease control.) Group 7 and 11 fungicide. 12-hr reentry.
  • P h-D WDG at 6.2 oz/A for Alternaira or gray mold. May be applied on the day of harvest. Group 19 fungicide. 4-hr reentry.
  • Pristine at 14.5 to 18.5 oz/A within 14 days of harvest for gray mold and blue mold. Do not use more than two (2) consecutive applications or more than four (4) times/year. Can be used day of harvest. (Consider other products if it was used in the orchard for disease control.) Group 7 + 11 fungicide. 12-hr reentry.
  • ProBlad Verde at 40 to 45.7 fl oz/A for Botrytis. Needs 8 to 12 hours dry time to absorb into treated tissue. Do not use within one day of harvest. Group BM01 fungicide. 4-hr reentry. O
  • Syllit FL at 3 pints/A plus another fungicide. Do not apply within 7 days of harvest. Group U12 fungicide. 48-hr reentry.
  • Topsin M WSB at 1 lb/A for pears and at 0.75 to 1 lb/A for apples. Do not use more than 4 lb/A/season or within 1 day of harvest. Do not use at any time in the orchard if your packing house uses a benzimidazole (such as Mertect or Decco Salt 19) postharvest. Group 1 fungicide. 2-day reentry.
  • Ziram 76 DF at 6 lb/A for gray mold. Do not use within 14 days of harvest. May irritate the skin of people who harvest fruit. Group M3 fungicide. 48-hr reentry.
• Thermo-nebulization where compounds such as fludioxonil (eFog80, ScholarEZ) or pyrimethanil (eFog160) are applied by chemical companies to rooms filled with fruit. Thiabendazole (TBZ) is commonly applied together with fludioxonil to enhance protection against bulls' eye rot. It is recommended to fill rooms as quickly as possible and apply the fungicide shortly after harvest to obtain better control.
• Drenched or spray with a fungicide suspension immediately after harvest. Make sure all fruit surfaces are covered well. Drenches tend to be better than sprays. Rotate fungicides from different FRAC groups every year. Avoid using the same fungicide twice on the same fruit. Resistance to fungicides has been detected in Washington.
  • Academy packing-line spray at 16 fl oz/200,000 lb fruit or as a 15 to 30 second dip at 16 fl oz/100 gal water. Use agitation to keep in suspension. Registered for several diseases. Group 3 + 12 fungicide.
  • BioSpectra 100 SC at 57 to 114 fl oz/100 gal water. O
  • Captan 50 WP at 2.5 lb/100 gal water. Group M4 fungicide.
  • Penbotec 400 SC at 16 to 32 fl oz/100 gal water for dip (wash) tanks or drenchers. Soak for at least 30 seconds then drain fruit. Concentration should be maintained at 500 to 1,000 ppm. (Consider other products if Inspire Super was used in the orchard for disease control.) Registered for blue and gray mold. Group 9 fungicide.
  • Scholar SC at 10 to 16 fl oz/100 gal of an appropriate carrier for bin, truck or in-line dip/drench. Use at 16 to 32 fl oz/200,000 lb fruit as an in-line aqueous or fruit coating spray. Do not expose treated fruit to sunlight. Registered for both apple and pear. Group 12 fungicide.
  • Sodium hypochlorite (Agclor 310 at 1.125 to 1.5 gal/1,000 gal water for apples or 1.5 to 2.25 gal/1,000 gal water for pears). Filtration of the wash water will help reduce the total amount of chlorine needed.
  • Sodium orthophenylphenate (Moldblock or Steri-Seal). Use Steri-Seal D at 1 gal/63 gal water. Dip fruit for a maximum of 1 min and then rinse immediately.
  • Thiabendazole (TBZ) still provides efficacy against bulls' eye rot and other pathogens that have not develop resistance. Resistance to TBZ in gray and blue molds is common in Washington and Oregon. Group 1 fungicides.
    • Decco Salt No. 19 at 575 g/250 gal water.
    • Decco Salt No. 38 at 575 to 1,150 g/300 gal water. Washington only.
    • Mertect 340 F at 16 fl oz/100 gal water.
    • Shield-Brite TBZ is also registered. See label for details.
• Fruit Wraps can be used for several storage problems of pear.
  • Pear Wrap III is treated with both ethoxyquin and copper. Do not re-use wraps.

Biological control

• Bio-Save 10 LP (Pseudomonas syringae strain ESC-10) at 500 g/80 gal water. Suspend in water for 10 to 30 min before use and agitate periodically. Dip or drench at least 1 min. Rated as moderately effective. O
• Botector (Aureobasidium pullulans strains DSM 14940 and 14941) at 6 to 14 oz/A depending on water volume as a preharvest application to control postharvest problems. Can be applied day of harvest. Compatible with sulfurs, oils and a few fungicides but not with many synthetic fungicides. Efficacy has been limited and inconsistent. 4-hr reentry. O
• Nexy (Candida oleophila Strain O) at 0.9 oz/20 gal water is registered for Botrytis cinerea (gray mold) and Penicillium expansum (blue mold). Dip or drench between 30 seconds and 2 min.

References Ali, E.M., Pandit, L.K., Mulvaney, K.A., and Amiri, A. 2018. Sensitivity of Phacidiopycnis spp. isolates from pome fruit to six pre-and postharvest fungicides. Plant Disease 102:533-539.

DeShields, J. B. and KC, A. N., 2021. Morphological and molecular characterization of Alternaria spp. isolated from European pears. Plant Disease, 105:2531-2540.

KC, A. N., and Rasmussen, A.L. 2019. First Report of Diaporthe rudis Causing Fruit Rot of European Pears in the United States. Plant Disease 103:2132.

Ozturk, I. K. and Amiri, A. 2020. Pathogenicity and Control of Phacidium lacerum, an Emerging Pome Fruit Pathogen in Washington State. Plant Disease 104:3124-3130.

Rosenberger, D. A., Forster, H., Prusky, D. B. and Adaskaveg, J. E. 2022. Postharvest Diseases of Pome Fruits. In Adaskaveg, J. E., Forster, H., and Prusky, D. B., editors. Postharvest pathology of fruit and nut crops. Principles, concepts, and management practices. St. Paul, MN: APS Press.