1996 CORNELL FRUIT HANDLING AND STORAGE NEWSLETTER

 

Items of Interest for Storage Operators

in

New York and beyond.

 

 

Chris Watkins

Department of Fruit and Vegetable Science

Cornell University

Ithaca, NY 14853

 

 

 

Item

Page

 Here we are again  2
 Comments on the 1995/1996 storage season
 Carbon dioxide injury on Empire apples
 Diphenylamine (DPA) maintains fruit firmness?
 Controlling postharvest decays and diseases on apples
 New biocontrol fungicides registered for postharvest uses
 Standard CA recommendations
 Comments on use of low oxygen storage
 0.7% oxygen for control of superficial scald on 'Delicious' apples
 Managing moisture losses during storage
 Literature that you should have 11 

 

 Mention of specific trade names or omission of other trade names does no imply endorsement of products mentioned or discrimination against products not mentioned.

Here we are again

 

After a three year absence, the Cornell Fruit Handling and Storage Newsletter is being re-established, and a tradition initiated by Bob Smock in 1956 and carried on over many years by Dave Blanpied will continue. I have found that these newsletters form a valuable repository of information about research affecting the New York industry over many years and I hope that they continue to do so in the future. It is my intention to provide annual summaries of research findings that affect grower and storage operator decisions about harvest and storage procedures and practices. In addition, I hope to have regular contributions from colleagues such as Jim Bartsch and Dave Rosenberger, as well as from outside Cornell.

 

 

Comments on the 1995/1996 storage season

 

In general the 1995/1996 storage season was free of major problems, despite some concern about flesh firmness. Firmness did not seem to be as much of a problem for storage operators who utilized rapid cooling and rapid CA (7 days or less between picking and 5% oxygen)

Low oxygen and high carbon dioxide injury were observed in fruit from some storages. In one case, low oxygen injury was observed in 'Empire' fruit from an operator using standard CA, probably because fruit were harvested late and an excessive delay occurred between picking and establishment of CAs.

High carbon dioxide injury occurred predominantly on 'McIntosh' apples. The most critical factor with this variety is the need to keep carbon dioxide concentrations low (2-3%) during the first 4-6 weeks of storage, and then allowing it to increase to 5% for the remainder of the storage period. Remember that carbon dioxide is beneficial for maintaining firmness of this variety, so ensure that the recommended concentrations are maintained. Other factors that influence susceptibility of fruit to the disorder are storage of immature fruit, delays in removal of field heat, rapid CA if carbon dioxide concentrations exceed those of oxygen, and a cool growing season. Research with diphenylamine (DPA) on the 'Empire' cultivar, used for scald control, indicates that DPA may prevent carbon dioxide injury (see next section), but no research has yet been done on 'McIntosh'.

 

 

Carbon dioxide injury on Empire apples

 

In the last few years, carbon dioxide injury has been noted on 'Empire' apples, especially by storage operators using rapid CA procedures. Ken Silsby and I have found:

1. Fruit are most susceptible to carbon dioxide injury during the first four weeks of storage. In this respect, 'Empire' apples are similar to 'McIntosh' apples and indicates the need for tight control of carbon dioxide concentrations in the storage atmosphere during this time. Research from Michigan highlights the need the keep carbon dioxide concentrations lower than those of oxygen during the first month of storage.

2. A postharvest drench of 1000 ppm DPA which is used for prevention of superficial scald will also control carbon dioxide injury.

3. Holding fruit at cold storage temperatures in air before application of either 2% or 5% carbon dioxide will reduce susceptibility of fruit to injury (Table 1). However, a delay of 10 days will also result in a significant loss of fruit firmness.

Our recommendation is that operators ensure tight control of carbon dioxide concentrations in the storage atmosphere and ensure that they are maintained less than those of oxygen during the first month of storage. If DPA is being used for scald control, carbon dioxide concentrations may be less critical. Some operators have expressed concern about decay in drenched 'Empire' apples. On page 6 Dave Rosenberger outlines the importance of DPA concentration, and we are continuing research to address this problem.

Table 1. Effect of delays at 32°F in air on incidence of external carbon dioxide injury and flesh firmness of 'Empire' apples stored in 2% or 5% carbon dioxide (in 2% oxygen) for 20 weeks. Average of two orchards

 

 Delay at32°F  External carbon dioxide injury(%) Flesh firmness(1lb)
 air  2%CO2  5%CO2  2%CO2  5%CO2
 1  59  59  16.4  16.5
 4  52  52  16.0  16.2
 10  3  3  15.5  15.2

.

 

 

 

Diphenylamine (DPA) maintains fruit firmness?

 

While carrying out the research on the effect of DPA on carbon dioxide injury on 'Empire' apples, we observed that fruit treated with DPA were often firmer than untreated fruit. Last season we treated fruit from 16 orchards in western New York with DPA. Firmness of DPA-treated fruit was 0.9 lb firmer than untreated fruit, but this varied by orchard. Treated fruit from two orchards were not different from untreated fruit, but nine were more than 0.9 lb firmer and of these two were more than 2.0 lb firmer.

We believe that this benefit may be significant for some growers, especially those meeting export standards. Research will continue to examine the effects of DPA on fruit firmness, especially in relation to interactive effects with calcium treatments, and fungicide treatments (see the article by Dave Rosenberger).

Controlling postharvest decays and diseases on apples

-contributed by Dave Rosenberger

 

Postharvest decays and diseases fall into two general categories: Diseases initiated in the field prior to harvest, and decays initiated during harvest and storage. Diseases initiated in the field include bitter rot, black rot, white rot, and pin-point scab (also known as storage scab). All of these diseases must be controlled with fungicides applied during the growing season. When these diseases appear in stored fruit, the cause can usually be traced to inadequate fungicide protection in the orchard during the last few weeks before harvest. At harvest, recently-infected fruit will either show no symptoms or will have visible infections that are too small to be noticed. Some of the black rot decay that develops in storage might also be traceable to gaps in fungicide protection during June and July, but more research is needed to determine if early-summer black rot infections can remain quiescent and cause decays after harvest.

In May of 1995, we collected 'Empire' fruit from two large storages in western New York. The fungi causing decays in 118 apples were isolated and identified. Forty-six percent of the decays from one storage and 36% of the decays from the other storage were field-initiated decays (mostly black rot and bitter rot). Thus, field-initiated decays can account for a significant proportion of the total postharvest decays observed in some lots of fruit.

Fungicides applied as postharvest treatments do NOT eradicate infections of field-initiated diseases. Apple growers, not storage operators, are responsible for protecting fruit against these diseases.

Decays initiated during harvest and storage are usually caused by Penicillium expansum and Botrytis cinerea. Both of these pathogens infect primarily at wounds or bruises, but Botrytis can infect undamaged fruit. Penicillium is the most common pathogen in fruit that receive a postharvest treatment whereas Botrytis is more common if fruit receive no postharvest treatment. Penicillium generally causes a watery soft rot, sometimes with visible white mycelium and blue sporulation on the fruit surface around a wound. Fruit infected with Botrytis may have gray mycelium around the wound. However, Botrytis-infected Empire fruit coming out of CA storage in spring often have a firm tan decay that involves the entire fruit. Apples with blue mold have a musty odor and flavor whereas apples with gray mold have a sweet "cidery" flavor (for anyone who wishes to identify decays by tasting them!).

Postharvest fungicide treatments can be used to prevent decays caused by Penicillium and Botrytis. Postharvest fungicide treatment is essential whenever diphenylamine (DPA) is used to control storage scald on apples. The recirculating drench solutions accumulate spores of Penicillium and Botrytis and inoculate wounds incurred during harvest and transport. In most cases, there is no reason to apply a postharvest fungicide if DPA is not needed. By moving fruit directly from the field into storage without any postharvest drenches, growers can avoid inoculating fruit with Penicillium or Botrytis, and the incidence of decay is often lower than in fruit drenched with DPA plus a fungicide.

Ten years ago, growers had a choice of using Benlate, Topsin M, or Mertect 340F in postharvest treatments. Today, Mertect 340F (thiabendazole or TBZ) is the only one of the three that is still registered. Captan is also registered for postharvest use and can be added to the DPA/Mertect solution. Researchers in Israel have reported that captan is reasonably effective against Penicillium when used at the full label rate of 2.5 lb Captan 50W per 100 gallons. In the U.S. where captan has usually been tested at lower rates and in combinations with one of the benzimidazole fungicides (Mertect, Topsin M, or Benlate), captan has provided no benefits compared to using the benzimidazole fungicide alone. Where TBZ (Mertect 340F) and DPA are properly applied, there is no advantage in adding captan to the drench solution.

The following guidelines should be followed whenever postharvest treatments are applied to apples of any variety:

1. Never mix any chlorine products with DPA/fungicide treatments. Chlorine-based disinfectants may react with and inactivate DPA and TBZ. Chlorinated water containing 100 ppm free chlorine is an effective disinfectant and is recommended in the water flotation tanks on packing lines, but chlorination treatments are not recommended for fruit going into storage. (Using chlorinated drinking water to make up postharvest drench solutions should not be a problem because chlorine levels in drinking water are very low.)

2. Always apply DPA and TBZ together. Neither product should be applied alone in a postharvest drench. Some isolates of Penicillium and Botrytis are resistant to TBZ, but the TBZ-resistant isolates are usually controlled by DPA. Thus, both TBZ and DPA are required to control the full spectrum of isolates.

3. Cool treated fruit as rapidly as possible after treatment. DPA effectively controls TBZ-resistant pathogens only at temperatures below 36-40 F. If apples are cooled slowly, TBZ-resistant Penicillium can initiate decays before the antifungal activity of DPA "kicks in".

4. Keep drench solutions agitated: With Mertect 340F, inadequate agitation in the drench tank will prove disastrous because all the active ingredient will settle to the bottom of the tank. The best system for agitating drench tanks involves the use of a high-volume pump to recirculate water through PVC "jets" that direct water flow across the bottom of the reservoir tank and create turbulence within the tank. An agitation system should be considered inadequate if it is not capable of resuspending virtually all of the sediment from the bottom of the tank when the system is activated after an over-night shut-down.

5. Keep drench solutions clean: Soil introduced into the postharvest treatment tanks carries decay inoculum and makes it more difficult to keep postharvest chemicals in suspension. A pre-wash with a high-volume stream of non-recycling water may be needed to remove soil from bins or equipment before they enter the postharvest drencher. Empty and clean tanks at least as frequently as is required on the DPA labels.

6. Keep drench solutions properly recharged: The drench solutions should be regularly recharged according to instructions included on the postharvest labels of the products being used.

Should 'Empire' apples receive postharvest DPA/TBZ drenches? 'Empire' apples rarely develop scald when grown under NY conditions and therefore do not require DPA treatment for scald control. Since the early 1990's, many packinghouse operators have been moving 'Empire' fruit directly into CA storage without any postharvest treatment. Some operators have been very satisfied with the low incidence of postharvest decays in untreated fruit whereas others have gone back to treating 'Empire' fruit because they encountered intolerable levels of decay in 'Empire' fruit that had not been treated. Although there are some exceptions, the current trend is that Hudson Valley growers have not experienced significant decay problems with untreated 'Empire' fruit whereas storage operators in western and central New York feel the postharvest DPA/fungicide treatment is needed to suppress decays.

As Chris Watkins noted in earlier sections of this newsletter, 'Empire' fruit treated with DPA do not develop carbon dioxide injury and, in some cases, treated fruit have maintained better fruit firmness during storage. Thus, postharvest DPA/fungicide treatments applied to 'Empire' may have several benefits in addition to controlling decay.

DPA has generally been recommended at 1000 ppm for 'Empire' fruit. All of the tests run by Chris Watkins and by Dave Blanpied were run using this concentration. However, in a test that I ran in the early 1980's, I found that the decay control achieved with a DPA/fungicide mixture was improved when DPA was used at 2000 ppm instead of 1000 ppm. Thus, storage operators who are concerned about decay problems in 'Empire' fruit put into long-term CA storage may wish to experiment with the higher rate of DPA on part of their crop. We are not aware of any adverse effects of using the high rate of DPA, but more research is needed to determine if there are consistent benefits from using 2000 instead of 1000 ppm of DPA on 'Empire' fruit.

 

 

New biocontrol fungicides registered for postharvest uses

-contributed by Dave Rosenberger

 

Three new postharvest fungicides have been registered for apples and pears during the past 18 months. All three of the new fungicides are "biocontrols". That means that the products are not traditional fungicides that act by killing fungal spores or inhibiting spore germination. Instead, the three new products are formulations of bacteria or yeasts - living organisms that actually grow on the fruit after they are applied. These biocontrol organisms stop decays by colonizing the wounds on apple fruit where decays are usually initiated. The biocontrol organisms apparently use up all of the available nutrients in the wounds, leaving nothing to support growth of the decay fungi.

Two products, BioSave-10 and BioSave-11, are both bacteria, were registered by EcoScience Corporation, and are targeted for apples and pears respectively. The third biocontrol, Aspire is a formulated yeast, Candida oleophila. Aspire was registered by Ecogen Inc., Langhorne, PA and is being marketed by Decco Division of Elf-Atochem North America.

The effectiveness of these biocontrol products under east-coast conditions remains unclear. The level of control achieved is sometimes slightly better than, but often considerably less than that achieved with TBZ. However, combinations of the biocontrols plus TBZ have frequently provided better control than can be achieved with either product alone. Combinations probably work well because TBZ suppresses spore germination during the period immediately after application when the biocontrol organisms are colonizing wounds. Once established, the effectiveness of the biocontrols does not fade in long-term storage like TBZ sometimes does. The biocontrols are effective against both wild-type and fungicide-resistant isolates of the pathogens.

None of the biocontrol products are being actively tested or marketed in the Northeast at this time. I am uncertain whether the producing companies have even applied to register their products in New York State. In citrus and apple packinghouses on the west coast, these products are being used in non-recirculating sprays on pre-sizing lines. As a result, the products are being priced at levels that may be prohibitive for the high-volume drenchers commonly used here on the east coast. Further research and interaction with the producers will be needed to encourage east-coast distribution and pricing for these biocontrol fungicides and to determine the appropriate use recommendations for eastern apple growers.

 

 

Standard CA recommendations

 

For storage operators using daily manual adjustments, or those not requiring long term CA storage, storage atmospheres and temperatures are as indicated in Table 2. Note that in the Champlain Valley region, oxygen concentrations in the upper part of the 2-3% range should be used. Regular monitoring of fruit for condition is strongly recommended, even when low oxygen storage is not being utilized. Note that low oxygen injury can occur even at normal (2-3% oxygen) conditions when fruit condition is not optimal, e.g. late harvest and excessive delay between picking and establishment of CAs.

Table 2. Recommendations for controlled atmosphere storage of New York apple varieties.

 Variety  CO2(%)   O2(%)  Temp (F)
 Cortland

 5

or2-3

 2-3

or2-3

 36

or32

 Delicious  2-3  2-3  31-32
 Empire  2-3  2-3  35
 Idared  2-3  2-3  31-32
 Jonagold  2-3  2-3  31-32
 Jonamac  2-3  2-3  31-32
 MaIntosh  2-3 one month,then5  2.5-3  34-38
 Macoun  5  2-3  36
 Mustsu  2-3  2-3  31-32
 Rome  2-3  2-3  31-32
 Spartan  2-3  2-3  31-32

 

Comments on use of low oxygen storage

 

We continue to encourage the use of low oxygen CA (1.5% oxygen, 2.0% carbon dioxide, 34F) for storage of 'Empire' apples. Many years of research have shown that these atmospheres are safe and will keep fruit of this variety in excellent condition until June or later. Problems were encountered in stored fruit from the 1992 harvest season, which followed a particularly cool and cloudy growing season, highlighting the need to be flexible in storage decisions in some years.

For most 'McIntosh' strains, maintain oxygen at or above 2%. The Marshall strain has a less porous skin and higher oxygen concentrations are required for safe storage. Dave Blanpied recommended use of 3%, but we have had reports of off-flavor development even at higher oxygen levels. Our current recommendation is 4% oxygen. Continue to use the temperature you have found to be safe (34-38F). Use 2-3% carbon dioxide for the first six weeks, then raise it to 5%.

'Delicious', 'Jonagold', 'Law Rome', 'Mutsu', and 'Spartan' will probably tolerate and benefit from use of 1.8% oxygen, according to extensive studies by Dave Blanpied.

Computerized gas analysis/control is essential for low oxygen CA. This storage regime should not be used if oxygen concentrations are maintained by daily manual adjustments. Fruit condition must also be monitored monthly - any loss of varietal flavor or development of alcoholic off-flavors indicates that low oxygen injury has started to develop. If this occurs, oxygen levels can be adjusted to 2%, and the alcohol levels and fruit flavor will return to normal.

Remember that rapid cooling is essential and rapid CA is highly desirable (7 days or less between picking and 5% oxygen).

 

 

0.7% oxygen for control of superficial scald on 'Delicious' apples

 

There is continuing concern that the industry will lose DPA as a postharvest drench for control of superficial scald because of concerns about chemical residues on fruit. 'Delicious' apples appear to be very tolerant of low oxygen storage conditions, and in British Columbia all but one packhouse has moved to use of 0.7% oxygen for scald control and stopped using DPA. The question is whether or not we can use a similar treatment regime in New York. In 1995 we tested 'Delicious' fruit from 18 orchards (9 strains) in cooperation with Lake Ridge Storage. We found that scald was totally controlled in 11 orchards, and the average incidence was 2% compared with 43% in air stored fruit. Low oxygen injury occurred at low levels in six orchards. Retention of fruit firmness was excellent: fruit lost only 0.9 lb firmness during six months of storage (average 16.8 lb at harvest).

More research is required to investigate safety of this storage technique and no recommendation is made for its use at this time.

 

 

Managing Moisture Losses During Storage

-contributed by James A. Bartsch

 

Moisture loss can be minimized by maintaining a consistent and high relative humidity (RH) in the apple storage room. At the same time, it is necessary to avoid condensation and free water contact with the produce because this will increase spoilage. In commercial storage practice there is often a narrow humidity range which divides the benefits of reduced shrinkage from the risks of increased spoilage. For most fruit and vegetable commodities the recommended storage RH level is around 95%.

The most critical factor in managing moisture loss in refrigerated storage is to design and operate the refrigeration system to maintain a high RH in the store room. This is accomplished by carefully controlling the temperature difference (TD) between the atmosphere in the store room and the refrigerant in the cooling coil. A large TD means the coil is much colder than the atmosphere in the store room and consequently, much of the moisture from the atmosphere is condensed or frozen on the coil in the refrigeration process. The result is reduced humidity in the store room and greater shrinkage of the apples. When the TD is small, less water is removed in the refrigeration process, and the RH inside the store room is maintained at a higher level.

To maintain a suitable TD in a direct expansion refrigeration system, an evaporator pressure regulator (EPR) should be installed in the suction line down stream from the evaporator. Each evaporator has its own EPR and store rooms serviced by the same compressor room may be operated at different temperatures and suction pressure settings. The EPR is adjusted to precisely maintain the correct evaporator suction pressure for the desired storage temperature and RH levels.

The EPR should be installed in parallel with a bypass solenoid valve which is held open during room loading and closed as soon as the fruit reaches storage temperature. The open bypass valve allows the coil to operate at the lowest suction temperature developed by the compressor and this provides maximum cooling during pulldown. Closing the bypass valve after the pulldown period enables the EPR to regulate the coil temperature independently of the suction line pressure developed by the compressor.

If a direct expansion system is retrofitted with an EPR, the work should be done by a qualified refrigeration technician. It may be necessary to make other alterations to the system to successfully incorporate the EPR into the system. It may not be possible to install an EPR on small systems like those used in walk-in coolers.

Flooded evaporator systems and systems using secondary refrigerants like chilled glycol usually vary the refrigerant temperature according to the cooling load. These systems automatically operate at the minimum TD needed to maintain desired room temperature. This guarantees maximum RH levels in the store room at all times.

Since water is removed from the atmosphere only when the refrigeration system is operating, minimizing the run time effectively reduces moisture loss from the fruit during storage. Cooling loads can be reduced through fan cycling practices and this reduces moisture loss and conserves energy during storage.

Supplemental humidification systems are not widely used in refrigerated and CA storage of apples. Experience with apple storage indicates that properly designed and adjusted refrigeration systems are capable of storing fruit for 200 days with less than 5% moisture loss. Cultivars like Golden Delicious are protected with a pallet cover after field heat removal to reduce weight loss during storage. Supplemental humidification should never be used if the refrigeration system is not designed to maintain high storage humidity levels in the first place. Adding moisture to a refrigerated store room with a large TD coil will create more problems than it will solve, and the added moisture will end up as ice on the coil, with little if any RH benefit being noticed by the fruit. The problems with reduced coil efficiency, more frequent defrosting, and increased energy consumption will negate any perceived humidity improvements. It is virtually impossible to solve low RH problems caused by poor refrigeration system design with supplemental humidification.

Some fruit storage operators allow the defrost melt water to remain inside the CA room to "humidify" the storage. This practice is very ineffective because surface little evaporation takes place at the low temperatures and relatively still conditions near the floor of the storage room.

Storage operators on the west coast frequently spray their wooden bins to partially moisten the wood before loading the fruit into storage. I am not aware of any studies, but in theory, depending on the bin type and style, dry wooden bins can absorb 25 to 40 pounds of water after being placed in high humidity cold storage. If bins have been rained on while standing in the orchard or if fruit and bins are dipped prior to storage, bins will be partially wetted and will absorb less moisture from the fruit.

 

 

Literature that you should have

 

Bartsch, J.A. and G.D. Blanpied. 1990. Refrigeration and Controlled Atmosphere Storage for Horticultural Crops. NRAES-22. 45p.

Blanpied, G.D. and K.J. Silsby. 1992. Predicting harvest date windows for apples. Cornell Information Bulletin 221. 12p.

Stiles, W.C. and W.S. Reid. 1991. Orchard Nutrition Management. Cornell Information Bulletin 219. 22p.

 

 

 

These are available from:

The Resource Center
Cornell Cooperative Extension
PO Box 3884
Ithaca, NY 14852-3884
email: resctr@cornell.edu
Phone: 607-255-2080
fax: 607-255-9946
web: www.cce.cornell.edu/store

 


 

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