Postharvest Practices to Minimize Decay in Pears
Drenching Strategies for Pears
- If pears will be packed soon after harvest and rain does not occur during harvest, a drench may not be desirable. If mucor is a serious potential problem, drenching may increase infection by spreading spores. Most winter pears are not drenched in bulk bins prior to packing. Most pears are rapidly cooled and placed into storage and packed as soon as possible. A fungicide and antioxidant are applied during packing.
- Prestorage heat treatments may be used for Anjou and Bosc pears. Heat in 80°F air for 2 days just prior to rapid cold storage. Treat fruit with a fungicide prior to heating. Heat will control mucor rot and side rot but not blue mold or gray mold. Do not use heat treatment on late-picked, overmature fruit.
Fungicide Drenches to Control Blue Mold and Gray Mold on Winter Pears
See the label for restrictions and directions for use. Constant agitation is required. Do not treat for more than 3 minutes. With certain products the addition of a wetting agent may be advisable. Do not use chlorine in drenches with fungicides. Thiabendazole (TBZ) sold in the Pacific Northwest as Mertect 340-F, Deccosalt 19, or Brogdex 594-F or 597-F. Only one application of Mertect 340-F can be made to pears after harvest. Only 30 bins of fruit may be treated with Deccosalt 19 per 100 gallons of liquid. Prior to application of Brogdex 594-F or 597-F, wash and rinse fruit and eliminate rinse water.
Packingline Treatments for Winter Pears
Chlorine. In the dump tank use sodium hypochlorite or calcium hypochlorite at 100 ppm available chlorine. Do not use chlorine with lignin sulfonate. Monitor concentration of chlorine many times each day. Add chlorine continuously with a pump rather than just once a day. Keep chlorinated dump tank at pH 6-8 for best results. Do not acidify solutions containing sodium silicate.
The surfactant AG98 (Rohm and Haas) improves the effectiveness of chlorine. Use 0.3% of AG98 and increase the initial chlorine charge by about 10X to obtain 100 ppm chlorine. For pears, allow about 1 hour for flotation salt to dissolve and tank specific gravity to stabilize between adjustments.
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SOPP. In immersion-type dumpers, use SOPP (Steri-Seal D or Stop Mold F) at 0.4% to kill spores of decay fungi. This is 1-1/4 gallons (22.6% a.i.)/100 gallons of water. Follow label directions.
Rinse with fresh water after treatment; test SOPP concentration daily, recharge if needed, replace frequently; if the dump water is above 70°F, reduce concentration to 0.2-0.25%, if above 80°F, do not use SOPP. In some years Bartletts are very susceptible to SOPP injury; if a packinghouse plans to use higher rates or more than one SOPP treatment during the packing cycle, consult the SOPP manufacturer for instructions. See section on flotation materials for pears for more information on flotation salts and fruit injury.
If using SOPP, dump tank water may be sterilized with heat. Remove all fruit from tank, cover tank with Styrofoam or canvas, heat to 130°F and hold at that temperature for 25 minutes. Allow water to cool before dumping fruit into it. Ensure good ventilation during heating. Approximately 10% water loss and 25% SOPP loss occurs during heating, requiring their replacement. Do not heat water containing chlorine.
Chemical Strategies to Control Superficial Scald on Winter Pears on Line
Ethoxyquin. Use 2700 ppm; apply as a spray on a brush bed on conveyor rolls or mixed with wax. Apply within one week of harvest for best control. Ethoxyquin-impregnated paper wraps are an alternative but may not be used on pears already treated with ethoxyquin. Only one application of ethoxyquin may be made to winter pears.
Application of Fungicides to Winter Pears on the Packingline
It is advisable to apply a fungicide on the packingline due to the long delay between packing and shipment. The fungicide may be applied as a line spray mixed with water or with wax in the packinghouse. Alternatively, you may use a wax in which a fungicide is premixed. When a fungicide is mixed with water, you may wish to include a wetting agent. Consult label for directions and cautions. Constant agitation is required.
Thiabendazole (TBZ) sold in the Pacific Northwest as Mertect 340-F, Deccosalt 19, or Brogdex 594-F or 597-F. Only one application of Mertect 340-F may be made to pears after harvest. Mertect may not be mixed with wax; Deccosalt 19 can be mixed with water.
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Captan 50W at 2.5 lbs./100 gallons or Captan 80W at 1.6 lbs./100 gallons. Recharge suspension when water volume in tank is reduced by 25%, add 1.0 lb. of Captan 50W or 5/8 lb. of Captan 80W per 25 gallons water added. Captan should be applied only to fruit that will be shipped soon after packing. Paper treatment with oil should not be used with Captan-treated fruit.
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Brogdex 360-F, a resin-based wax containing TBZ fungicide.
Flotation Materials for Pears
Special Notes on Handling Winter Pears
- Do not pack fruit while wet. Dry thoroughly before storage. To avoid staining, do not wrap wet pears in copper-treated paper. Keep relative humidity in storage only high enough to avoid shrivel. Low oxygen (1%) atmosphere will reduce stem-end decay of pears.
- Copper-treated wraps reduce spread of gray mold and mucor rot. Be sure the fruit is dry before wrapping to avoid copper injury.
- Proper sanitation, removal of bruised and injured fruit, good storage practices and the effective use of SOPP or chlorine are the only measures available for control of mucor rot, alternaria rot, cladosporium rot and side rot.
Storage Room Management to Reduce Decay
- Clean cold room thoroughly with a high pressure hose and a commercial disinfectant labeled for food handling areas. Several formulated products are available for this purpose. Most of these products contain sodium or calcium hypochlorite, chlorine dioxide, organic acids such as phosphoric or acetic acid or quaternary ammonia compounds often referred to as quats.
- Keep temperature in cold room as low as possible.
- Use packaging material that minimizes bruising and injury of fruit during transit.
- Handle fruit gently and carefully.
- Keep fruit cold.
Dr. Eugene Kupferman, Postharvest Specialist
WSU Tree Fruit Research and Extension Center
1100 N. Western Ave., Wenatchee, WA 98801
Tree Fruit Postharvest Journal 4(1):10-11