1997 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
Voice: 607-255-1784; Fax: 607-255-0599
E-mail: cbw3@cornell.edu

and

David Rosenberger
Cornell's Hudson Valley Laboratory
PO Box 727, Highland, NY 12528
Voice: 914-691-7231; Fax: 914-691-2719
E-mail: dar22@cornell.edu

 

 

 

Item

Page

 Comments on the 1996/1997 storage season . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

 2

 DPA effects on McIntosh and Empire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

 4

 Comments on Postharvest Decays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

 5

 Varietal requirements and responses to CA storage . . . . . . . . . . . . . . . . . . . . . . . . . .

 12

 

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

 

Comments on the 1996/1997 storage season

 

Comments from Chris:

Firmness issues, primarily for 'Empire' apples, continue to be a problem for the industry. It is difficult to know whether maintenance of firmness is becoming more difficult each year or if we are just becoming more aware of it because of export quality standards. Many growers are having relatively few problems meeting firmness requirements while others are having frequent problems. Preharvest factors, especially the cool, cloudy growing season in 1996, may have been important as lower photosynthethic rates result in less carbohydrate (energy) being transported into the fruit. We are finding very little evidence that calcium is an important factor in maintaining firmness. If you are having firmness problems, review all your handling practices. Minimizing time between harvest and cooling, and achieving rapid CA, are perhaps the most critical factors. However, it is not enough to just have the fruit in cold storage. You should check your cooling capacity and be sure that the system is not overloaded. Remember that rapid cooling is difficult to accomplish with the fast filling of rooms necessary for rapid CA storage because rapid filling places increasing demands on available refrigeration capacity. Actually, fruit may take two to three times longer to cool under rapid CA storage conditions than under the slower "normal" rate of traditional loading systems, if refrigeration systems are inadequate. Remember also that rapid CA refers to the process whereby the time between harvest of fruit and achievement of 3 to 5% oxygen in the storage atmosphere of the storage room is kept to seven days or less. It does not refer to how quickly the atmosphere can be reduced once the room is filled.

A second problem around the state this season was development of breakdown in CA-stored McIntosh around late April/early May. In some, but not all instances, the breakdown occurred in spur types which ripen earlier than the standard types. We do not recommend CA storage of early ripening strains of McIntosh beyond February/March, but many storage operators have not had losses with long-term storage of these strains during previous seasons. Problems with standard McIntosh types are more difficult to explain as they have occurred in fruit from well run operations. Again an unknown seasonal factor may be involved. The possibility exists that quality of fruit from these blocks is usually not as good as other fruit even in 'normal' years, but problems are only detected in bad storage years when senescence progresses to the stage that breakdown is detectable. The best way to minimize future risk is to ensure that all stored fruit are identified by orchard block. Identification of orchard blocks which produce fruit with poorer storage quality would allow earlier marketing of those fruit in future years.

A third problem, low oxygen injury, has occurred sporadically around the state and has affected some fruit exported to Europe. One operator employed storage conditions (2% oxygen and 2% carbon dioxide) that have been identical for at least the last three years and we found no evidence of prolonged periods of oxygen below 2 %. The operator maintained an excellent sampling system during storage and therefore detected the problem early enough to save most of the fruit. Unfortunately the reasons for the low oxygen problems have not always been clear. One factor may have been that fruit were more mature than ideal for storage at 2% oxygen. In 1996, earlier-than-normal ethylene production was measured in fruit samples during harvest which may indicate that fruit were sometimes more mature than realized based on other maturity indices.

The possible solutions for addressing low oxygen problems are:

1. Maintain current practices, making sure that only early-harvest fruit are kept at 2% oxygen, and hope that the problem does not reoccur. Ensure, however, that sampling of representative samples is carried out to detect any development of injury (loss of varietal flavor and development of alcoholic off-flavors);

2. Raise oxygen atmospheres to 2.5%, undoubtedly the safest method to avoid problems. Any effect on flesh firmness is likely to be minimal.

3. Increase storage temperatures by a degree or two. The lower the temperature, the greater the risk of low oxygen damage occurring.

My personal view is that storage operators who are not using computer-controlled facilities should take the option of maintaining oxygen concentrations closer to 2.5% than 2%.

Another instance of low oxygen injury is worth mentioning. In this case, it seems that the Empire apples involved were suffocated by dirt in the postharvest drench tank. Given the increasing concern about food safety it would be wise to ensure that solutions are remade regularly and kept clean. Fungicides, especially TBZ (=Mertect 340F) probably settle out more quickly and therefore become ineffective for rot control when drench water becomes dirty.

Item 4: Although the incidence of external carbon dioxide injury was generally low this season compared with last season, an interesting case occurred where high levels of injury were found on Empire apples that were air stored in cartons destined for Europe. In addition I have received reports that losses of fruit in Europe, early in the export season, due to this disorder have appeared in the past. It seems hard to believe that cartons of fruit accumulate sufficiently high carbon dioxide concentrations to cause injury, and no measurements have yet been made. However, carbon dioxide injury has been a long-term problem for southern hemisphere exporters of apples if temperature control and ventilation are not optimal in the shipping boxes. We are planning to carry out research on this issue in the coming season. The short term solution - any fruit exported when fruit susceptibility to carbon dioxide injury is greatest, i.e. during the first month after harvest, will be unlikely to develop carbon dioxide injury if treated with DPA to prevent scald development.

 

Comments from Dave:

In recent years, most of the serious postharvest decay problems in New York State have involved Empire fruit that were held in storage for six months or more. Significant losses are sometimes noted with other varieties as well, but the postharvest decay problem with Empire has been more persistent and has required more attention.

The most difficult dilemma involves deciding whether or not to apply postharvest treatments to Empire fruit before storage. Treating these fruit increases the incidence of fruit decays caused by Penicillium, whereas moving Empire into storage with no postharvest treatment has resulted in significant losses to Botrytis. Fruits infected with Botrytis remain firm, have a tan "baked apple" appearance, and frequently have no wound that can be identified as the entry point for the fungus. At the moment we do not know how the fungus gains entry to the fruit or where the Botrytis inoculum originates. A multi-year research program is being initiated to devise new controls for Botrytis on apples. In the meantime, decisions on whether or not to treat fruit should be based on previous experiences in each packinghouse. Some operators swear they will never go back to drenching Empire whereas others are convinced that they need a postharvest drench to control Botrytis.

Some storage operators continue to use postharvest drenchers with either no agitation systems or with inadequate agitation systems. The fungicide Mertect 340F appears to settle out of suspensions much more completely than did Topsin M or Benlate. As a result, the first time that a drencher is shut down for the night, the fungicide in the tank settles to the bottom and stays there unless the tank contains an agitation system that can really churn all of the water in the tank and thereby re-suspend the material that has settled to the bottom. Drenchers that do not have good agitation systems are totally obsolete and will create more problems than they solve.

 

DPA effects on McIntosh and Empire

 

Last year we reported that Empire fruit collected from 17 orchards in fall of 1995, treated with 1000 ppm DPA for control of superficial scald, and stored under CA (2% oxygen / 2% carbon dioxide) averaged 0.9 lb greater firmness than nontreated fruit at the end of the storage season. In addition, DPA prevented development of external carbon dioxide injury.

This result raised a couple of interesting questions:

1. Given that storage operators have assumed that calcium salts, usually applied with DPA and fungicide, may have given them a beneficial effect on firmness, what are the relative effects of DPA and calcium?

2. In McIntosh apples we recommend that carbon dioxide concentrations are kept below 2 to 3% during the first 30 days to prevent carbon dioxide injury. Concentrations then are allowed to rise to take advantage of better firmness retention at 5% carbon dioxide. These recommendations were developed before common use of DPA for scald control. If DPA prevents carbon dioxide injury, is it then possible to take advantage of higher carbon dioxide concentrations to maintain firmness?

Results with Empire collected from four orchards in fall of 1996 were not conclusive because DPA-treated fruit, either with or without calcium, stored at 2% oxygen / 2% carbon dioxide at 36 °F, tended to be alcoholic. In our experiments we used fruit from the later part of the harvest window, and the most mature fruit developed the most severe problems. The results confirm that later harvest fruit should not be stored at oxygen concentrations close to 2%, and that DPA may aggravate the risk of problems occurring in these fruit.

The McIntosh results were exciting however. Fruit from four orchards were treated with either (1) water, (2) 1000 ppm DPA, (3) calcium chloride, (4) TBZ (=Mertect 340F), or (5) DPA, calcium and TBZ combined. Fruit were then stored for seven months in 2.5% oxygen with 2.5% or 5% carbon dioxide. Firmness of McIntosh apples was the same when treated with water, calcium or TBZ, but about 0.7 to 0.9 lb firmer when treated with DPA either alone or with calcium. Fruit kept at 5% carbon dioxide were 0.4 lb firmer than fruit kept at 2.5% carbon dioxide. No carbon dioxide-related or any other disorder was detected in these fruit. No recommendations are made at this time as follow up studies are planned. However, the data obtained to date suggest that if you are treating your fruit with DPA, you may not need to be too concerned with maintaining low carbon dioxide early in the storage period. My perusal of storage logs indicates that more often than not, carbon dioxide concentrations are often too low early in the storage period, and some loss of firmness may be a consequence.

 

Comments on Postharvest Decays

Postharvest decays can be divided into two broad categories. The first category includes the summer fruit rot diseases that are initiated in the field but sometimes cause decays that appear during storage. The second category covers diseases that are initiated during or after harvest.

Fruit decays initiated in the field include bitter rot, black rot, and white rot. All of the summer fruit rots must be controlled with fungicides applied during the growing season. The presence of summer fruit rots in fruit coming out of storage is usually an indication that fungicide protection in the orchard was not adequate during the last few weeks before harvest. Fruit infected shortly before harvest either show no symptoms or have visible infections that are too small to be noticed by fruit pickers. 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.

Decayed Empire fruit were collected from storages in western New York in May of 1995. Isolations were made from each decayed fruit and the pathogens were identified. We found that 36-46% of the decays in those samples were caused by the summer fruit rots (Table 1). This unusually high incidence of summer fruit rots on fruit coming out of storage was consistent with what happened in the field in 1994. Summer fruit decays (especially black rot) appeared in many orchards during late summer of 1994. Thus, it was not surprising that some fruit had latent infections that appeared only after fruit were harvested.

Fungicide programs were adjusted in 1995 to provide better control of black rot. The modified fungicide programs (and perhaps differences in weather during the growing season) resulted in a significantly lower incidence of summer fruit rots when fruit came out of storage in 1996. In decayed Empire fruit collected in May of 1996, the summer rots accounted for less than 10% of postharvest decays in seven of the eight storages where samples were collected (Table 1). Fruit from one storage in western NY still had summer rots causing 20% of postharvest decays, thereby indicating a need for better management of summer fungicide programs.

 

 

Table 1. Relative incidence of postharvest decays caused by various pathogens as determined by isolations made from decayed Empire fruit collected from two apple storages on 9 May 1995 and from eight apple storages 9-10 May 1996.
     

1996
 

1995
Mean of five WNY storages Highest incidence WNY Mean of two HV storages
  WNY-a* WNY-b      
 Percent of total decays:          
  Bitter rot. . . . . . . . . . . . . . . . 3 13 2 7 2
  Black rot. . . . . . . . . . . . . . . . 6 26 2 7 1
  White rot. . . . . . . . . . . . . . . 4 2 1 6 2
Total percentage of postharvest decays caused by summer rots. . . . . . . . . . . . . . 13 41 5 20 5
 *WNY=western New York apple storages; HV=Hudson Valley apple storages; Samples from each storage consisted of approximately 100 decayed fruit.

Decays initiated during harvest and storage are usually caused by Penicillium expansum, Botrytis cinerea, and Alternaria species. All of these pathogens infect primarily at wounds or bruises. Penicillium causes blue mold. Affected fruit have a watery soft rot, sometimes with visible white mycelium and blue sporulation on the fruit surface around a wound. These are the fruit that commonly sink to the bottom of water-flotation dump tanks. Fruit infected with Botrytis may have gray mycelium around the wound, and the disease is commonly called gray mold. Fruit with gray mold are often soft, but Botrytis-infected Empire fruit coming out of CA storage in spring can have a firm tan decay that allows the apples to float out of the dump tank and onto the packing line. 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!).

Penicillium is the most common pathogen in fruit that receive a postharvest treatment before storage whereas Botrytis is more common if fruit receive no postharvest treatment. Four of the packing houses surveyed in May of 1996 were packing Empire that had received a postharvest treatment of diphenylamine (DPA) plus thiabendazole (TBZ). Empire from the other four packing houses had not received any postharvest treatment. Penicillium accounted for almost twice as much of the decay in treated fruit as in nontreated fruit, whereas Botrytis was seven times more common in nontreated than in treated fruit (Table 2). The proportion of decayed fruit (as a percentage of total fruit stored) was not determined in our survey, so we have no data to indicate whether postharvest treatments reduced the total incidence of decay. However, none of the storage operators using postharvest treatments were completely satisfied with the results, so one must conclude that the standard postharvest treatments were only partially effective at best.

Table 2. Relative incidence of postharvest decays caused by Penicillium expansum and Botrytis cinerea as determined by isolations made from decayed Empire fruit collected from two apple storages on 9 May 1995 and from eight apple storages 9-10 May 1996.
 

1995

1996
Postharvest fungicide treatment applied. . . . . . . . . . . . . . . . . . . . . . . No Yes No Yes
Number of storage surveyed. . . . . .  1 1 4 4
Percent of total decays:        
Penicillium. . . . . . . . . . . . . . . . . . .  9 32 35 58
 Botrytis. . . . . . . . . . . . . . . . . . . . . .  36 15 37 5
 Total % Penicillium or Botrytis . . .  45 47 72 63

Botrytis is commonly considered a wound pathogen, but many of the decayed Empire fruit from which we isolated Botrytis had no visible wounds. Infections on these fruit seemed to originate from the stem end. We do not know if the infections actually originated with the stem or if the fungus gained entry through microscopic cracks in the stem cavity of the fruit. Postharvest treatment with DPA plus TBZ provided reasonably good control of Botrytis. Note that in 1996 Botrytis was recovered from only 5% of decayed fruit from packing houses that applied a postharvest treatment (Table 2). As noted above, however, problems with Penicillium are increased when postharvest treatments were applied.

Fungicide-resistance may be at least partially responsible for increasing problems with postharvest decays. The fungicide resistant strains of Penicillium and Botrytis that were detected in the late 1970's were resistant to all the benzimidazole fungicides including TBZ. In the mid-1980's we discovered that most of the fungicide-resistant strains of Penicillium and Botrytis were unusually sensitive to DPA. Thus, the combination of DPA plus a benzimidazole fungicide continued to provide good control of Penicillium and Botrytis through the late 1980's.

Even in the mid-1980's, however, we found that about 2% of the P. expansum strains in apple storages were resistant to the combination of DPA plus a benzimidazole fungicide. In recent years, the DPA/TBZ combination has allowed increasing levels of decay to develop in treated Empire fruit. I suspect that the pathogen strains with resistance to both DPA and TBZ have gradually increased in importance and are responsible for declining effectiveness of the postharvest treatments.

In some cases, control failures may be attributable to inadequate concentrations of TBZ in the drench tank, either because the material was not replenished, or because it settled to the bottom of the tank and was not re-suspended by the agitation system. For example, in one storage, only 27% of the Penicillium isolates recovered from decayed fruit were fungicide resistant despite the fact that fruit had been given a postharvest fungicide drench. Thus, 63% of the decays were caused by strains of the pathogen that were susceptible to TBZ and would have been controlled if TBZ had been applied properly. By comparison, 95% of the Penicillium decays in another storage were caused by strains of the pathogen that were resistant to TBZ, presumably because TBZ was applied more effectively in the second storage.

Improved sanitation may be required to manage postharvest decays as fungicide-resistant strains of Penicillium begin to predominate and the DPA/TBZ treatment loses effectiveness. No single fungicide or practice is likely to replace TBZ in the near future. Rather, over-all management practices may need to be adjusted to compensate for reduced effectiveness of postharvest fungicides.

Spores of both Penicillium and Botrytis can be disseminated on air currents or in water dumps or drench solutions. Prior to our most recent survey, I assumed that most fruits that became infected with Penicillium encountered the spores in the postharvest drencher solutions. Thus, I was surprised to discover as a result of our surveys that Penicillium caused 21 to 60% of the decays in packing houses where fruit had not received a postharvest treatment. The infections in untreated fruit must have been caused by air-borne spores that landed on fruit at some point during harvest, transport to storage, or during storage. The relatively high incidence of Penicillium decay suggests that levels of air-borne inoculum must be relatively high. Infections resulting from airborne spores could be eliminated or at least reduced if effective sanitation measures were developed to reduce air-borne inoculum. The benefits of sanitation measures have been clearly demonstrated in citrus storages where a different species of Penicillium is the primary pathogen. However, there is no data from apple storages to show how much benefit might be gained from sanitation measures that might reduce airborne inoculum of Penicillium and Botrytis.

Penicillium spores can survive through summer on dry bins stored outdoors and also on storage walls, packing house equipment, and any flat surface that accumulates dust in a packing house. Careful cleaning of the packing house should significantly reduce inoculum levels. Weekly cleaning may be necessary during late winter and spring to minimize the accumulation of spores that is likely to occur when fruit coming out of storage has a higher incidence of decay.

Quaternary ammonium compounds are generally recommended for cleaning storage walls and are available from agrichemical suppliers. Follow label directions and precautions carefully. All surfaces must be free of visible dirt or fruit-decay residue before the disinfectants are applied because the disinfectant activity will be neutralized before it can penetrate through several levels of dirt or accumulated residue.

Using chlorinated water in packing house water dumps may help to disinfect bins as they are emptied. (Again, research data is lacking!) Chlorinated water will not penetrate decayed fruit, so decays that are left in the bottoms of the bins as they come out of water dumps will continue to sporulate after the empty bins are removed from the packing house. Decayed fruit left in bins will provide an abundance of inoculum for infecting fruit as bins are filled the next year. Thus, all rotten fruit should be removed from empty bins as they come out of the water dumps, and areas of the bin that were in contact with the decays should be rinsed again with chlorinated water after the decays are removed from the bin floor.

Decayed fruit should be removed from packing houses as quickly as possible to reduce the amount of spores that they can release into the packing house air. Bins that are "sanitized" by going through a chlorinated water dump can become re-contaminated if they are left in the packing house adjacent to areas where decayed fruit are being removed from the packing line.

Biocontrol fungicides have been registered for postharvest use on apples for several years and may eventually provide an alternative for TBZ. Biocontrol fungicides are formulations of bacteria or yeasts- living organisms that actually grow on the fruit after they are applied. Unfortunately, we still lack basic information on effectiveness and optimum use-strategies for biocontrol fungicides. Biocontrols do not act by killing pathogen spores or inhibiting spore germination. Instead, they stop decays by colonizing the wounds on apple fruit where decays are usually initiated. The biocontrol organisms apparently utilize all of the available nutrients in the wounds, leaving nothing to support initial growth of the decay fungi. The decay fungi use the apple juice and damaged cells in wounds as a source of nutrients for initial growth of spores that land in the wounds. When this "start-up fuel" is consumed by the biocontrol fungi, the pathogens are left without the nutrients needed to initiate growth. This mode of action for biocontrols dictates that biocontrol fungicides will have good protectant activity but virtually no eradicant activity. If Botrytis or Penicillium become established before the biocontrol is present, then the decay fungi will usually predominate and continue to invade and decay the fruit flesh.

One biocontrol product, Decco I-182, is now registered in NY State and should be available for use this fall. Decco I-182 was formerly marketed as 'Aspire'. It is a formulated yeast of the species Candida oleophila. This strain of the yeast was initially isolated from tomato fruit and grows best between 55°F and 88°F. Thus, it may function best if it can colonize wounds during the period when fruit are cooling down. (One wonders if perhaps rapid cooling may reduce effectiveness of the biocontrol by rapidly creating sub-optimal conditions for colonizing wounds.)

Decco I-182 can be used as the sole fungicide in a postharvest drench or line spray, but it will probably perform best when applied with TBZ. When used with TBZ, the TBZ should suppress spore germination (of TBZ sensitive isolates) during the period immediately after application while the biocontrol organism is still colonizing wounds. Once established, the effectiveness of the biocontrol should not decline in long-term storage like TBZ sometimes does. We do not know if using TBZ with Decco I-182 will provide any benefits where TBZ-resistant strains of the pathogen predominate.

Decco I-182 can be ordered through agrichemical suppliers but will not be warehoused with other agrichemicals. Because Decco I-182 is a living organism, it must be kept refrigerated until it is used. When this product is ordered, it will be shipped directly from the manufacturing plant to the purchasers in insulated containers. Drench solutions that include Decco I-182 will have a characteristic yeasty odor that some individuals may find offensive, but the odor apparently is not retained on treated fruit.

Traditional postharvest fungicides include only TBZ (Mertect 340F) and captan. TBZ is the only benzimidazole fungicide still registered for postharvest treatment of apples and should always be used in combination with DPA. Captan 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, captan has provided no benefits compared to using the benzimidazole fungicide alone. As the 1996 Food Quality Protection Act is implemented, Captan may once again come under close regulatory scrutiny. Thus, the Captan label will very likely be revised sometime in the next 3-5 years and some currently labeled uses might be eliminated.

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. (Using chlorinated drinking water to make up postharvest drench solutions should not be a problem because chlorine levels in drinking water are very low.) 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.

2. Always apply DPA and TBZ together. Neither product should be applied alone in a postharvest drench. Some isolates of Penicillium and Botrytis that are resistant to TBZ will be 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. TBZ-resistant pathogens that are sensitive to DPA will be controlled only at temperatures below 36-40°F. If apples are cooled slowly, TBZ-resistant Penicillium can initiate decays before temperatures are low enough for DPA to have any effect.

4. Keep drench solutions agitated: With Mertect 340F, inadequate agitation in the drench tank will prove disastrous because all of 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.

 

Varietal requirements and responses to CA storage

 

The 1972 bulletin on "Controlled Atmosphere Storage of Apples" is being revised by Chris Watkins and Dave Blanpied, and will be available for purchase shortly. Recommendations have been altered to reflect changes in the industry, including varieties and marketing conditions. In this issue of the Cornell Fruit Handling and Storage Newsletter, updated information by variety is provided for your information (Table 3).

Cortland. CA storage allows marketing of Cortland until March. Fruit should be treated with diphenylamine (DPA) to prevent development of superficial scald. Although Cortland is often stored at 32°F, it may be temperature sensitive. Experimental work has shown that in some years low temperature breakdown may appear as early as December/January when Cortland apples are stored at 32°F. Low oxygen conditions may increase low temperature breakdown and vascular browning. Cortland is preferably stored under the same CA storage conditions as McIntosh. Large fruit are prone to bitter pit and senescent breakdown.

 

Delicious. CA delays the onset of mealiness and lengthens the shelf life of Delicious apples. The variety is particularly susceptible to scald and must be treated with DPA prior to storage. In British Columbia, oxygen concentrations of 0.7% are used to control scald without DPA. However, this technique is still being evaluated for safety under New York conditions and should not be attempted by storage operators. Storage at oxygen concentrations of 1.5% are safe for early harvested Delicious apples if rapid CA procedures are followed.

 

Empire. A 2.5% oxygen concentration is safe and effective for CA storage of Empire, but reducing oxygen concentrations to 2% will improve fruit firmness. At least 1% carbon dioxide is necessary to obtain maximum fruit firmness, and at 2.5% or more the risk of internal carbon dioxide-related disorders increases. Therefore we recommend that carbon dioxide concentrations be kept closer to 2% than 3%.

Although Empire has also been stored with good results at 1.5% oxygen under commercial conditions, off-flavors have been observed occasionally even with 2%. Early harvest, application of rapid CA procedures and computer control of atmospheres will reduce risk of injury. The constancy of the oxygen level is important at 2% or below as large fluctuations of oxygen can be a problem.

Low ethylene technology is used for storage of Empire apples by several storage operators. Benefits of low ethylene storage are sometimes better than those obtained using low oxygen storage.

Empire apples are susceptible to flesh softening and flesh breakdown. In Western New York, but not in the Hudson Valley, breakdown can usually be controlled by early harvest and normal CA. In the latter region, however, one observation indicates that breakdown is reduced by low oxygen storage, and controlled by rapid CA. Breakdown is also controlled by low ethylene storage.

The recommended storage temperature for Empire apples is 34°F to 36°F, representing a compromise between excessive loss of firmness at higher temperatures and risk of chilling related injuries at lower temperatures.

Empire has a low susceptibility to scald, and DPA treatment can be avoided. However, application of DPA for scald control appears to reduce susceptibility of fruit to external carbon dioxide injury and improve maintenance of fruit firmness.

Some storage operators successfully store Empire apples with McIntosh. However, because high carbon dioxide levels typical of McIntosh rooms may aggravate development of internal browning disorders, fruit in such rooms should be stored only for two to three months.

 

Fuji. Although there is little research available for fruit grown in New York State, the variety stores well under both air and CA conditions. Development of internal carbon dioxide injury has been reported elsewhere, especially with late harvested fruit.

 

Gala. Little research is available for fruit grown in New York State, but experience elsewhere indicates that Gala is tolerant of low oxygen and moderate carbon dioxide concentrations. Gala should be stored in 2 to 3% oxygen and 2 to 3% carbon dioxide at 32°F without difficulty. It may be possible to store the variety with McIntosh, but storage operators should test small lots first. Gala has a short storage life. It tends to lose flavor after about four months of CA storage. DPA is not required since scald susceptibility is slight.

 

Golden Delicious. The advantages of CA storage for Golden Delicious are similar to those for Delicious. However, the variety is prone to skin shrivel, which can be prevented by stapling polyethylene film over the tops of bins. Care must be taken to avoid condensation which can result in fruit splitting and increased decay. Therefore, polyethylene hoods should be applied only after the field heat has been removed from the fruit. Using polyethylene can aggravate scald on this variety.

 

Idared. Although Idared stores well in air storage, it can develop breakdown and Jonathan Spot. Both problems can be delayed or controlled by CA storage. Idared may be chilling sensitive. Brown core and firm flesh browning have been reported in fruit stored at 32°F, but usually not at 34-36°F. The variety does not require treatment with DPA for scald control. Low oxygen storage in 1.5% usually is safe. Avoid carbon dioxide concentrations greater than 3%.

Since this variety is picked late in the season, it may be frozen in the orchard. Unlike Northern Spy, Idared recovers from these light freezes. Nevertheless, severely frozen apples should not be stored longer than late December.

 

Jonamac. CA storage will maintain quality of Jonamac, but it will lose flavor with prolonged storage. Fruit should not be stored beyond December. Jonamac can be stored under McIntosh CA conditions, but are not chilling injury sensitive.

 

Jonagold. This variety is especially susceptible to loss of texture and development of breakdown in air. CA storage at 2 to 3% oxygen and 2 to 3% carbon dioxide at 32°F may be essential to ensure marketability of the variety beyond November. Fruit of large size and with watercore are susceptible to breakdown.

 

Law Rome. Law Rome apple respond well to CA even though they store well in air. This variety is particularly susceptible to scald and must be treated with DPA before storage.

 

Macoun. Macoun can be stored with McIntosh in CA at 38°C. The variety has sometimes developed serious internal carbon dioxide injury when stored at 32°F.

 

McIntosh. Use of CA storage is essential to maintain quality of this variety beyond November. In addition to maintaining firmness, CA storage reduces brown core and scald development. Rapid CA is essential. DPA should be used after a hot, dry growing season in the Lake Ontario and Hudson Valley areas. However, most storage operators in the Champlain region are able to avoid DPA use for scald control. The traditional storage temperature for McIntosh is 38°F. Reducing the temperature results in firmer fruit, but the risk of chilling disorders increases. Nevertheless, many operators are successfully storing McIntosh at 36°F, and even lower. A few operators have successfully stored McIntosh at 32°F for several seasons. The risk of problems occurring are reduced with shorter storage periods than with long term storage, but temperatures should be raised to 38°F as oxygen concentrations are reduced to 2%. Operators storing fruit under CA beyond March should maintain higher storage temperatures.

McIntosh are particularly sensitive to external carbon dioxide injury, which usually occurs in the first 30 days of CA storage. However, fruit firmness is greater when fruit are held at 5% than 2 to 3% concentrations of this gas. As a result, it is recommended that fruit be stored in 2 to 3% carbon dioxide for the first month of CA storage, after which it can be raised to 5%. Injury can occur, however, even when recommended levels of carbon dioxide are used. When used for control of scald, DPA may reduce the risk of external carbon dioxide injury and reduce the need for lower carbon dioxide concentrations early in the storage period.

Most strains of McIntosh that have been tested can be stored safely at 2 to 3% oxygen, although early ripening strains such as Macspur and Spurmac appear to have more limited storage potentials. The Marshall strain, however, has lower skin porosity than other strains, i.e. the resistance to gas movement through the skin is low, and therefore Marshall McIntosh must be stored at higher oxygen concentrations. Initial recommendations were for storage of Marshall McIntosh at 3% oxygen. However, as a result of further trials and industry experience, the recommended oxygen concentration is now 4 to 4.5%. Riper fruit at harvest appear most prone to low oxygen injury in storage.

 

Mutsu (Crispin). Yellow and oversized apples are susceptible to breakdown. DPA fixes green color and prevents yellowing of apples in storage.

 

Spartan. Although Spartan is susceptible to carbon dioxide injury, it has been stored successfully under the same conditions as McIntosh. Spartan tends to shrivel at 36 to 38°F. Although they keep better at 32°F, the variety is sensitive to chilling injury.

 

Stayman. Responds well to CA storage. Although it will tolerate carbon dioxide concentrations of 5%, it is normally stored as a hard variety.

 

Other varieties. All other varieties grown in New York should be stored at 2 to 3% oxygen and 2 to 3% carbon dioxide at 32°F. However, before proceeding, check with your local extension agent for the latest recommendations. Apply DPA to scald-susceptible varieties.

Table 3: Atmospheric and temperature requirements for standard controlled atmosphere storage of apples.
 Variety Carbon dioxide (%) Oxygen (%) Temperature
° F
Low oxygen (1·5 - 1·8%) storage potential Low ethylene storage potential
 Cortland 2-3 2-3 32 no no
   2-3 one month, then 5  2-+3 36    
 Delicious 2 2 32 yes no
 Empire 2-3* 2 35 yes yes
 Fuji 2-3 2 32 yes ?
 Gala 2-3 2 32 yes no
 Golden Delicious 2-3 2 32 yes no
 Idared 2-3 2 34 yes no
 Jonagold 2-3 2-3 32 yes no
 Jonamac 2-3 2-3 32 no no
   2-3 one month, then 5  2-3 36    
 Law Rome 2-3 2 32 yes no
 Macoun 5 2-3 36 no no
 McIntosh  2-3 one month, then 5 3 36 no no
   2-3 one month, then 5 2 38    
 Marshall McIntosh strain  2-3 one month, then 5 4-4.5 36 no no
Mutsu  2-3 2 32 yes no
 Spartan 2-3 2-3 32 yes no
 Stayman 2-5 2-3 32 yes no
* If not treated with DPA, use 1.5 - 2% CO2 during first 30 days.


 

© Copyright by the Department of Horticulture Website at Cornell University.
Please direct comments/corrections to the Horticulture Department Web Team at Hort_Web@cornell.edu.
.
Home Page URL: http://www.hort.cornell.edu