Practices to Minimize Postharvest Decay of Apples and Pears
Use low angle nozzles to keep irrigated water off fruit on lower limbs to reduce sprinkler rot (Phytophthora cactorum). Maintain 1 ppm copper in the irrigation water.
Maintain good weed control and keep grass mowed. A drier orchard microclimate will reduce Mucor rot, Coprinus rot and scab.
Supplement fruit calcium with foliar sprays during the growing season. High calcium fruit is less prone to decay and physiological disorders than low calcium fruit.
Apply preharvest Ziram 4F (1 gallon/acre/application). Number of days from last spray to harvest is 0 for Ziram if under 18 pints/acre/season. A fungicide for scab may be needed if rain of sufficient duration occurs 2 to 4 weeks before harvest.
Use the minimum amount of nitrogen fertilizer necessary to maintain plant vigor. High nitrogen fruit are more prone to various postharvest problems than lower nitroge fruit. Application of nitrogen immediately postharvest may minimize fruit nitrogen while still supplying enough for fruit set and shoot growth the following year.
To avoid development of resistance in the packinghouse do not use Benlate or other benzimidazole fungicides in the orchard. Resistance to Benlate will reduce the effectiveness of other postharvest fungicides including Mertect 340-F and Deccosalt No. 19.
Harvest at proper maturity. Late-picked fruit is more susceptible to decay than fruit of optimum maturity.
Clean bins thoroughly before filling. Steam is most effective.
Reduce bin contact with dust and dirt which contain spores of decay fungi. Keep the bottom of bins as clean as possible. Keep staging areas mowed. Suppress dust.
Avoid picking fruit when it is wet.
Keep grounders (fallen fruit) out of bins.
Do not allow bins of fruit to remain in the sun. Transfer fruit quickly to the packinghouse and cold storage.
Handle fruit gently. Avoid bruising and stem punctures. Smooth orchard roads and driving forklifts slowly may reduce fruit injury.
After harvest, remove fallen fruit from orchard to prevent buildup of decay spores.
Apply copper at leaf-fall to help reduce bull's eye rot.
Use a fungicide and change solution regularly to avoid buildup of fungal spores such as Mucor that are not controlled by fungicides.
In the dump tank use sodium hypochlorite or calcium hypochlorite at 100 ppm available chlorine of SOPP (SteriSeal D or Stop Mold F) at 0.3 to 0.5% to kill spores of decay fungi. For pears, use sodium sulfate flotation salt with chlorine or lignin sulfonate (Orzan, Lignosite 458, Lignosite 50) with SOPP. Do not mix chlorine with SOPP. 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 to 8 for best results, but do not acidify solutions containing sodium silicate.
The surfactant AG98 (Rohm and Haas) improves the effectiveness of chlorine. Use 0.3% AG98 and increase the initial chlorine charge by about 10X to obtain 100 ppm chlorine. For pears, allow about I hour for flotation, salt to dissolve and tank specific gravity to stabilize between adjustments. Do not use surfactants with Topsin, Captan or Mertect.
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 and needs to be replaced. Do not heat water containing chlorine.
Minimize depth of immersion of fruit when dumping bins. Immersion forces contaminated water into wounds and cores and increases rot.
Fruit should receive 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.
Apply fungicide prior to storage.
Prestorage heat treatment may be used for Anjou and Bosc pears. Heat at 80°F for 2 days just prior to rapid cold storage. Fruit should be treated 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.
Clean cold room thoroughly with a high pressure hose and a commercial disinfectant labelled 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".
Do not pack and store wet fruit. Dry thoroughly before storage. Do not wrap wet pears in copper-treated paper or staining may result. Keep relative humidity in storage only high enough to avoid shrivel.
Keep temperature in cold room as low as possible.
Low oxygen (1%) atmosphere will reduce stem end decay of pears.
Copper-treated wraps reduce spread of gray mold and Mucor rot.
Use packaging material that minimizes bruising and injury of fruit during transit.
Handle fruit gently and carefully.
Keep fruit cold.
Mike Willett(1), Gene Kupferman(2), Rodney Roberts(3), Robert Spotts(4), Dave Sugar(5), Gary Apel(6), Hugh W. Ewart and Bill Bryant (7)
(1)WSU Cooperative Extension Agent, Yakima, WA; (2)Postharvest Specialist, WSU TFREC, Wenatchee, WA; (3)USDA Pland Pathologist, Tree Fruit Research Lab, Wenatchee, WA; (4)OSU Plant Pathologist, Mid-Columbia Research and Extension Center, Hood River, OR; (5)OSU Plant Pathologist, Southern Oregon Experiment Station, Medford, OR; (6)Michelsen Packaging Company, Yakima, WA; (7)Northwest Horticultural Council, Yakima, WA
Post Harvest Pomology Newsletter, 7(3): 5-7