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Monday, June 26, 2017

WSU-TFREC/Postharvest Information Network/Postharvest Practices to Minimize Decay in Apples



Postharvest Practices to Minimize Decay in Apples


Drenching Strategies

Evaluate whether a drench is needed. When Red Delicious are to be sold within 3 months of harvest, it may not be necessary to drench except in years of high scald potential. Many storage operators do not drench Golden Delicious with a fungicide prior to storage, except for fruit from those orchards which have a history of decay or in years of late season rainfall. Granny Smith apples should be drenched since the potential for scald is high unless ultra-low oxygen storage is used. Gala apples are not very susceptible to storage scald. Fuji and Braeburn are susceptible to scald and fruit stored for late season sales should be treated.

Chemical Control of Superficial Scald at Harvest

See the labels for restrictions and directions for use. Use a fungicide in all drenches and change the solution regularly to avoid buildup of fungal spores such as mucor that are not controlled by fungicides. Do not use chlorine in drenches with DPA.

Diphenylamine (DPA). Use 1000 ppm for Rome Beauty and Winesap; use 2000 ppm for Red Delicious; use 2200 ppm for Granny Smith. The concentration of DPA to treat Fuji and Braeburn has not yet been determined.


Chemical Control of Blue and Gray Mold at Harvest

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 two applications of Mertect 340-F can be made to apples after harvest. Only 30 bins of apples 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.

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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. Dump tank after 8 hours of use.


Packingline Treatments

Minimize depth of fruit immersion when dumping bins. Immersion forces contaminated water into wounds and cores and increases rot. Give fruit a thorough fresh water rinse after leaving the dump tank and flumes. Design line to minimize damage to fruit. Avoid sharp edges and drops that wound or bruise fruit.

Application of Fungicides in the Dump Tank

Chlorine. In the dump tank, use sodium hypochlorite or calcium hypochlorite at 100 ppm total chlorine. Monitor concentration of chlorine many times each day using a test kit that measures total chlorine. Add chlorine continuously with a pump rather than just once a day to avoid overloading the tank. Keep chlorinated dump tank at pH 6-8 for best results. Do not combine chlorine with any fungicide treatment, heat or acid in the dump tank. Change water in dump tank frequently to avoid salt buildup which can injure fruit.

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SOPP. In immersion-type dumpers, use SOPP (Steri-Seal D or Stop Mold F) at 0.33% which is 1 gallon (22.5% a.i.)/100 gallons of water. Dip fruit for 30-120 seconds; rinse with fresh water after treatment; test SOPP concentration frequently; recharge when 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.

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 building ventilation during heating. Approximately 10% water loss and 25% SOPP loss occurs during heating, requiring their replacement. Do not heat water containing chlorine.


Application of Fungicides on the Packingline

It may be advisable to apply a fungicide on the packingline. 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 it may be desirable to include a wetting agent. Consult label for directions and cautions. Constant agitation is required. Many packinghouses are no longer applying a fungicide if the fruit is to be shipped soon after packing.

Thiabendazole (TBZ) sold in the Pacific Northwest as Mertect 340-F, Deccosalt 19, or Brogdex 594-F or 597-F. Only two applications of Mertect 340-F may be made to apples after harvest. Mertect cannot be added to wax; Deccosalt 19 can be added to wax.

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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.

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Brogdex 360-F, a resin-based wax containing TBZ fungicide.

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Decco Apl Lustr-256, a shellac-based wax containing TBZ fungicide.

Dr. Eugene Kupferman, Postharvest Specialist

WSU Tree Fruit Research and Extension Center
1100 N. Western Ave., Wenatchee, WA 98801
Kupfer@wsu.edu

Tree Fruit Postharvest Journal 4(1):8-9
June 1993

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