Postharvest Applied Chemicals to Pears:
A Survey of Pear Packers in Washington, Oregon, and California
This report summarizes data on chemicals applied to pears after harvest. These data were obtained through in-person interviews conducted in the fall and winter of 1997 with packinghouse managers about chemicals used after harvest on Anjou, Bosc, and Bartlett pears grown and packed in California, Washington, and Oregon and harvested in the fall of 1996.
It does not include information on the storage and handling of organic fruit. The volume of pears marketed under the term "organic" is estimated at 130,380 boxes with 78% of those being Anjous from the Wenatchee District (Wenatchee River Valley and the Columbia River Valley north to the Canadian border). This is less than 0.8% of the total amount of pears marketed from the 1995 crop.
There were interviews with 18 packers about storage and packing of Anjou pears. Eleven packers were interviewed for information on Bosc and 16 packers were interviewed about Bartlett. In total, the pear packers interviewed accounted for 11,557,710 boxes (44 lb. net) of pears.
The survey was funded through the Environmental Stewardship Program of the Winter Pear Control Committee (WPCC) and the Environmental Protection Agency (EPA) via the National Foundation for IPM Education to obtain information about actual chemical use on pears to better understand the implications of possible regulatory action and to advance the goals of the Stewardship Program.
Chemicals are applied after harvest to protect the fruit against physiological disorders and diseases. Disorders include skin marking, storage scald, belt burn and a number of types of spotting. Diseases include decay caused by fungal organisms including Botrytis, Penicillium, Mucor, Phialophora, etc. Previous surveys have shown that a significant amount of losses occur to stored pears from skin discoloration or disease each season (Kupferman, TFPJ, April 1994). In many cases the use of chemicals postharvest is done as a prophylactic to protect against costly repacking or potential market adjustments as modern consumers require pears which are blemish and decay free. The absence of a fungicide on pears in storage for several months may result in entire bins or boxes of fruit with no commercial value when the fruit become infected with decay-causing fungi.
Losses to diseases or disorders were determined through industry surveys following the 1990-1993 crops (Table 1). Information from 22 of the 30 packers surveyed in reference to the 1993 crop indicated that decay was the most serious problem (cited in "Anjou Pear Quality-Final Report" by Kupferman et al., January 1995; see also TFPJ). Other reasons for losses of the 1993 crop were shriveling, skin speckling/skin marking, scald discoloration, and overripe. Only four of the 30 packers reported no losses from postharvest decay or disorders. Managers stated that the problem of decay has increased since the loss of the fungicide Benlate.
Table 1. Losses due to cullage from postharvest diseases and disorders as reported by packinghouse managers in the Pacific Northwest.
|Crop year||Total crop|
(44 lb. boxes)
|Total $ lost||$
(per packed box)
It is obvious that in the time period of the survey losses did not decrease, and the magnitude of the losses indicates a very serious industry problem. Although data for the more recent crop years do not exist, the magnitude of postharvest losses continues to be extremely serious as indicated by informal surveys.
There is a great deal of diversity in the methods used to store and pack pears. Pears are harvested in late summer or early fall and either packed immediately, as is typical for most of the Bartletts grown in California, or are stored. Pears may be stored in packed boxes, loose in bins as they come from the orchard, or in bins after sorting. They may be stored in regular atmosphere for a short period of time or in controlled atmosphere (CA) for up to 10 months. Pears may be jumble packed loose in a box, tray packed on fiber trays, or individually handwrapped. These decisions are based on the variety of pear, the experience of the packer, and the requirements of the market.
If further information is required, please contact the author (Dr. Eugene Kupferman, WSU-TFREC, 1100 N. Western Ave., Wenatchee, WA 98801, e-mail firstname.lastname@example.org).
|Background Information and Conventions Used in
It is important to provide a background to the chemicals used in this report, the terminology describing pear packing, and common nomenclature.
I. THE FRUIT
Pear production has centered on few cultivars of pears (Figure 1).
Figure 1. Pear varieties marketed fresh by Washington, Oregon, and California
The pear grown in most districts is the Bartlett pear (also known as 'Williams'). It is a "summer" pear in that it matures at the end of summer and has only a short storage life. Most Bartlett pears are sold by January.
The rest of the pears are considered "winter pears" and they mature in the fall and can be stored in CA storage at least until spring.
The dominant "winter pear" is the 'Anjou' or 'd'Anjou' pear. It can be stored for up to 10 months in CA storage, which enables it to be marketed up to the beginning of the following summer. It is a smooth, green-skinned pear with a rounded pear shape.
The 'Bosc' pear is a russetted, brown-skinned pear with an elongated shape, which makes it difficult to run over the packingline as the neck gets caught in the equipment. This pear is intermediate in storage potential as compared with Bartlett and Anjou. The volume of Bosc pears, even from CA storage, is depleted by early spring.
The Comice pear is grown in the Medford district as a gift pear. It is green skinned and has a plump teardrop shape. Most Comice pears have been sold by the end of February.
II. PEAR PRODUCTION DISTRICTS
Pears are relatively demanding with regard to their preferred soil and climate situation. Thus, each district has settled on pear cultivars that can grow well under conditions found in that district (Figure 2).
Figure 2. Map of the West coast, showing pear production districts.
Washington State has three growing districts. The northern district of central Washington State grows Anjou and Bosc pears. The Wenatchee River Valley grows Anjou pears with Bartlett pollinizers. The Yakima Valley grows Bartletts for cannery and a lesser amount of Anjou and Bosc.
Oregon has two growing districts. The Hood River District grows Anjou pears and a few Bosc. The Medford District concentrates on Bosc, Comice, and Seckel, as well as a few Anjous.
Pears are grown in California in the Lake District and the river district with Bartletts for the early market dominating. There is little controlled atmosphere (CA) storage for pears in these districts.
The production of pears has been on the increase over the last several years in all districts. Unfortunately, the same phenomenon has occurred in many other parts of the pear-producing world. Exports have helped stabilize prices, but with increasing international competition these markets have become increasingly demanding. Nontariff trade barriers as well as tariffs prevent the sale of U.S. pears in a number of potentially important markets. Consequently, competition is becoming increasingly fierce as buyers are becoming less willing to accept any pears with a blemish or decayed area.
IV. CHEMICALS AVAILABLE TO THE PEAR INDUSTRY
- Postharvest Fungicides
Sodium orthophenylphenate (SOPP)
Historical Perspective of SOPP in the Pear Industry. Prior to the invention of wet dumpers used to float the pears out of the field bins, SOPP was applied as a line spray to apples and pears. This was the practice as early as the mid 1940s. However, coverage was not as good as when applied in a shower drench or dump tanks.
When water dumpers came into the industry, this became the preferred method of application due to improved coverage of the fruit. Some packers kept using it as a line spray while others used it in the water system. Coating of the fruit was extremely important. The application of SOPP is always followed by a rinse of potable water due to fears of phytotoxic damage to the fruit.
With the advent of regulatory agencies, the application of SOPP was required to be followed by a potable water rinse to meet residue requirements. However, the residue level set by different agencies was never the same.
In Washington State, in the 1940-1960s the common practice was to apply SOPP to all varieties of apples and pears. These varieties were thick skinned with a waxy coating so phytotoxicity and decay susceptibility were low. However, over time the industry learned that Asian pears developed phytotoxicity very easily and use on these varieties was not recommended. It was determined that Bosc will show more damage than smooth-skinned varieties.
As the industry continued to change varieties and the length of storage continued to increase, the need to control decay and disorders (i.e., storage scald) increased. In the mid-1960s, DPA drenching evolved, and Benlate was substituted for SOPP in the drencher since it did not have to be rinsed. Over time Benlate lost some of its effectiveness, which was first noticeable on Golden Delicious. SOPP reemerged as the fungicide for use on apples, especially on Goldens as they were the first variety to develop decay in late storage when Benlate was used alone.
Throughout this period, SOPP was the main fungicide used on pears due to pear packing and storage practices. Specifically, pears were often packed in the fall into cartons and stored in packed boxes for shipment throughout the season. Apples were stored loose in bins and packed immediately prior to shipment.
Transition Period. When FIFRA (Federal Insecticide, Fungicide and Rodenticide Act) of 1989 was implemented, reregistration of SOPP was required. The cost of reregistration was very high, and the companies which produced technical grade material for SOPP were unwilling to support the entire cost of reregistration. The pear industry in the PNW through the Winter Pear Control Committee, a federal commodity commission, agreed to share the cost of reregistration.
The apple industry was unable to organize to support the higher cost of reregistration on apples as the cost of reregistration on apples was significantly higher than on pears due to the use of processed apple products. In addition, at this time, Benlate was still an effective way to control decay on apples.
Current Situation with SOPP. SOPP is registered nationally for use solely on pears. SOPP is labeled for use in a drench, line spray, or dip, providing it is followed by a potable water rinse. SOPP is widely used in western USA pear packinghouses. One estimate is that 80% of the winter pears in Washington and Oregon (50% of the Bartletts) are treated with SOPP. However, it is not as widely used in California due to problems associated with the disposal of wastewater.
It is not widely used as a bin drench largely because of the necessity of a post-treatment rinse. When not followed by a rinse, it can cause phytotoxicity even if applied at label rates. Current research with the drench application has shown that, when applied at less than label rates, residue of SOPP on the fruit is lower and phytotoxicity can be eliminated while still controlling fungal diseases without an immediate rinse.
In the pear industry, SOPP is typically used as a dip treatment in the initial stage of the packing process. It is applied in the initial water dump of the packingline, at the point in which the pears are floated out of the picking bin. It is generally used below the registered allowable concentration. It is most often used at 3300-3800 ppm as compared to the allowable label rate of 4900 ppm (Steri-Seal D).
It is not commonly used as a line spray in the Pacific Northwest at this time.
Industry sources testify to the effectiveness of SOPP in the control/suppression of the growth of fungi that cause decay in pears. Laboratory research has shown that SOPP is currently effective in the range of 90+% in controlling pear fungi. In commercial situations it is less effective due to application methods and the difficulty of controlling decay on fruit which has been inoculated prior to treatment. It is an essential tool in the control of decay, allowing for an extended marketing season for pears. This longer marketing period has allowed the industry to expand while remaining profitable.
SOPP is formulated and sold in Oregon and Washington State as Steri-Seal "D" and Stop-Mold "F" by Steri-Seal of Washington, Inc.
Thiabendazole (TBZ) is a fungicide approved for postharvest use on apples and pears as a drench, dip, or line spray. TBZ was discovered by Merck & Co. and is 2-4-thiazolyl-benzimidazole. It is in the same family as Benlate, Topsin-M, and other benzimidazoles, however it cannot form MBC (Carbendazim) (according to Merck). TBZ remains stable in an aqueous suspension throughout the storage life of the fruit. The active fungicide is thiabendazole, not a breakdown product.
TBZ is sold as Mertect by Novartis, Decco-Salt 19 by Atochem Co., and Britex 360-F (in combination with wax) by Brogdex, Inc.
It is relatively effective against Blue Mold, Bull's-Eye Rot, Gray Mold, Stem End, and Neck Rots. Pear growers are encouraged not to use any of the benzimidazole fungicides in the orchards to avoid the development of resistance to TBZ. However, recent informal surveys have shown that approximately 30% of Penicillium expansum spores collected from locally grown pears are not susceptible to control by TBZ. Control by TBZ appears to be breaking down.
Captan is not used in the pear industry to any great extent due to the desire to ship fruit internationally since many pear-importing countries do not permit Captan residues. Captan, however, is an effective fungicide and could be a part of an effective postharvest program for pears sold domestically.
The use of Captan in pear orchards can stain fruit, and it is also not registered for pre-harvest application. Its use after harvest can also be risky when combined with pre- or postharvest applied horticultural oil. This combination can cause damage if oil is applied together with the Captan or even several months prior to Captan use.
Chlorine is used in the pear industry to reduce or minimize the accumulation of fungal spores in water systems. In the northwest, the chlorine used most frequently is generated from sodium hypochlorite (bleach). In some California packinghouses chlorine is generated by using gaseous chlorine.
Sodium hypochlorite can cause damage to fruit when the sodium component accumulates in a water system and the salt level concentrates to the point at which salt burn occurs. Changing the water in the tank or flume and careful monitoring of the levels can minimize this problem. In all cases, rinsing with fresh water is necessary following the use of chlorine.
Chlorine is commonly used at 100 ppm to control fungal spores in water solutions with pears. It has no residual activity and is used most appropriately to kill fungal spores in water, rather than on fruit or within wounds, as it is bound up on exposed tissue.
It is most effective when the pH of the solution is close to 7.0. Thus, it is more effective in a dump tank when used with neutral pH dump tank amendments. It is not suitable for use with lignosite.
Since pears do not float in pure water, a salt is added to force the pears to the surface. Most flotation salts are added to water to achieve the specific gravity of 1.05; many pears will float in a less dense solution.
Calcium (or sodium) ligninsulfonate, commonly known as "lignosite," assists pears to float in a water system through its ability to change the specific gravity of the solution. This is a byproduct of the lumber industry and its content varies somewhat by the species of tree being used. In the pulping of wood, lignin is separated from the cellulose fibers, which are then used in the manufacture of paper. In this process, the lignins are solubilized and the products derived are referred to as lignin sulfonates. In addition to lignin sulfonates, the product contains small amounts of natural sugars. It is thought that this product possesses some fungicidal properties.
In the dump tank, SOPP is used with lignosite to reduce the number of spores and to prevent the solution from fermenting. The pH of a 0.35% SOPP solution in calcium ligninsulfonate is 9.0. Chlorine cannot be used with lignosite due to high organic matter and pH. A solution of lignosite with SOPP will last several weeks or longer. Thorough rinsing of the fruit is required to prevent skin marking.
Sodium sulfate is supplied as a powder and must be mixed prior to use. Either SOPP or chlorine can be used with sodium sulfate to reduce fungal spores. When SOPP is used with sodium sulfate, the pH is 9.7-10.7, but when chlorine is used the pH is 7.8. While it is difficult to dissolve in cold water, it dissolves adequately in heated water with agitation.
Sodium silicate is supplied as a liquid known as "water glass" or "pear float." When used with SOPP the pH is 10.7; when used with chlorine the pH is 11.2. It is slippery and spills are both dangerous and difficult to remove unless cleaned up promptly. Machinery must be rinsed well at the end of each shift.
The current regulations for disposal of sodium silicate solutions, as dictated by the Washington State Department of Ecology, indicate that a solution must have a pH between 6.0 and 9.0. Silicate solutions will form a gel below pH 9.0 when acidified if the specific gravity of the solution is above 1.03. Solutions of silicate will gel below pH 8.3 when the specific gravity is at 1.025.
Sodium carbonate (soda ash) has many industrial uses and consequently is readily available and inexpensive. It is a powder commonly available in 100 lb. sacks. It is somewhat caustic and will dissolve paint, corrode machinery, and can irritate workers' skin. It is difficult to dissolve unless made into a slurry, and it frequently cakes at the bottom of the tank. It is compatible with either chlorine or SOPP. A 5% solution of sodium carbonate in water with or without SOPP has a pH of approximately 10.
A Note about Flotation Salts and Fruit Injury. Any of the flotation salts may stain fruit surfaces if fruits are left in the flotation salts overnight or, at times, over a lunch break. SOPP alone can also injure fruit surfaces. Warm temperatures and/or higher concentrations will speed injury. Thus, dumping warm fruit into ambient temperature solutions can cause skin damage.
Acidification of a dump tank containing pear chemicals is not advised. When chlorine is used, acidification will cause the release of chlorine gas; acidifying SOPP can cause fruit damage and acidifying sodium silicate will cause it to form a gel.
Drench or dip: the process of showering fruit in bins with a chemical prior to storage.
Box: a corrugated container used for shipping pears. Boxes may be of various types of construction and design. They usually contain up to a bushel of pears. A bushel can weigh between 36 and 44 lbs. of pears net. It may or may not have a polyliner.
Polyliner: a plastic bag between the fruit and the corrugated box. It usually contains numerous 1/4 inch holes to facilitate gas exchange.
Bin: most of the pear industry in the Pacific Northwest uses a plywood bin, although plastic bins are increasing in popularity, especially in California. Although bin sizes vary between packinghouses, a "standard" size bin measures 48" x 48" x 36" tall. Many bins are rectangular rather than square to permit nesting of the empty bins.
Regular Storage: refrigerated storage, without atmosphere modification.
Controlled Atmosphere Storage: refrigerated storage coupled with control of oxygen and carbon dioxide.
Packer/Storage Operator: most packers operate their own storages. In the Pacific Northwest it is not very common to have fruit stored by a grower or third party, then taken for packing to a separate facility.
Postharvest Chemical Use on Anjou Pears
Anjou pears, or d'Anjou pears as the variety is also known, are grown in two major districts: the Wenatchee River Valley in Washington and the Hood River Valley of Oregon. These two districts account for 89% of all Anjou pears produced in the USA. California's Lake District, the Yakima Valley in Washington, as well as the Medford District in Oregon, although large pear-producing districts, do not have large volumes of Anjou pears (Figures 4 and 5).
Figure 4. Anjou pear shipments.
Figure 5. Volume of Anjou pears from each district.
The marketing season for Anjou pears ranges from soon after harvest in September to the middle of July the following summer. Thus, much of the fruit is stored in controlled atmosphere (CA) storage under very precise conditions.
I had the opportunity to meet with 18 packers of Anjou pears who in total accounted for 7,881,847 boxes (44 lb. net wt.) in 1996. This was a year of a short crop. However, I am confident that the chemical treatments were typical of current practices.
Half of the fruit was placed in regular storage and half was stored for a longer period in CA. Seven packers extended the marketing season of Anjou pears for 10 or more months, 8 packers marketed over 7 to 9 months and three packers marketed for less than 6 months. There was no difference in chemical use among the three groups.
Drenching Anjou Pears
When most tree fruits are received at a storage or packing facility, they are normally drenched with a fungicide and/or antioxidant to prevent disease or disorders. This is not the case with Anjou pears. It is the experience of many packers that when drenches are used fungal spores from infected fruit become distributed throughout the bin and other fruit run the risk of becoming infected. This is due to a lack of effective control measures, particularly the lack of effective fungicides.
The major fungicide used in the tree fruit industry is thiabendazole (TBZ), sold as Mertect, DeccoSalt 19, and Britex 360-F. It is the experience of the industry that Anjou pears treated at harvest with a drench of TBZ will frequently develop diseases caused by Penicillium expansum or Mucor spp., while fruit which has not been drenched may develop Botrytis cinerea. Late season sprays in the orchard have reduced the amount of risk from Botrytis to a low level. The same has not been accomplished with the other decay organisms. Recent tests have shown that up to 30% of the Penicillium spores are not susceptible to control by TBZ. Yet this is the only economically viable fungicide.
Thus, only 6.7% of the Anjou pears were treated at harvest with a drench of TBZ. This amounted to 531,405 boxes (44 lb.) treated by four packers in 1996. In most cases, when the Anjou pears were drenched the antioxidant, ethoxyquin was included. Both of these products were used in accordance with the label. Only in one case was TBZ used alone and on the entire crop. In all other incidences, these packers drenched only a portion of their fruit and this fruit was placed into CA storage.
Most Anjou pears are stored directly out of the orchard without drenching in wooden bins. Most of the bins had polyethylene liners or sleeves between the fruit and the bin to prevent scuffing. Few had bubble pads on the bottom of the bins. Most packers allow the growers to decide whether to use bin liners or bubble pads. There is very little use of plastic bins.
Most packers spread the fruit out 2-3 bins high in a number of different refrigerated rooms to cool the fruit overnight and then restack the fruit in the storage room when it is cool.
Packing Anjou Pears
Most packers start packing Anjou pears immediately after the fruit has been cooled, although in some cases a single packingline may be used alternately with apples and pears. If the packer has orders for export shipments early in the season, those will be filled first, otherwise the fruit which will be sold last is packed first.
Very few packers use presize equipment to sort pears. Those who do place the fruit back into bins and store the bins in CA until final packing. The vast majority of packers use the commit-to-pack system and store long-term CA fruit handwrapped in boxes.
Packers are attempting to store Anjou pears for a longer period of time loose in bins, which allows them more flexibility in the type of pack they put up (bags, overwraps, or trays, etc.). However, the storage of pears in bins presents significant challenges to reduce decay, minimize shrivel while in storage, and prevent scuffing during packing. The susceptibility to scuffing of Anjou pears increases the longer they are in storage.
Dump Tank Chemicals
Anjou pears are universally dumped from the bin into a water flume system. Since pears do not float in pure water, a salt is added to the water to increase the specific gravity. The choice of the flotation material is sometimes dictated by preference, but often it is dictated by the regulations for the disposal of packinghouse wastewater. Calcium lignosite (also known as calcium ligninsulfonate) is used in 68% of the packinghouses. Sodium silicate and sodium sulfate are each used in 16% of the packinghouses (Figure 6).
Figure 6. Volume of Anjou pears by flotation materials used in packinghouses.
On the basis of fruit volume, calcium lignosite is used on 68% of the fruit, sodium silicate is used on 19% of the crop, and sodium sulfate is used on 13%.
A fungicide or biocide is also used in the dump tank. In part, this additional chemical is present to reduce the concentration of fruit pathogenic fungal spores which may accumulate in the water, and it also prevents the flotation material from fermenting. When choosing a biocide, it is important that it be compatible with the chemistry of the flotation material.
Where lignosite is used, the pH of the flotation material is very high (alkaline) and chlorine is not effective. SOPP (sodium orthophenylphenate) is used in all cases where lignosite is the flotation material. Where sodium silicate is used, a third of the packers did not include a biocide, a third chose SOPP, and a third chose to use chlorine. Where sodium sulfate was used, two-thirds of the packers used chlorine, and one-third used SOPP. Here also the choice of the chemical used is dependent upon marketing strategy, downstream chemical application, and wastewater regulations.
Soap or Detergent
Anjou pears are removed from the dump tank by rollerbars that elevate the fruit out of the tank. Fruit are then rinsed with fresh water, which is not recycled, and often soap is sprayed on. There are a number of soaps or detergents used and the choice varies depending on the type of dirt remaining on the fruit, so the type of soap used may change during the season or even during a shift. Nine of the nineteen packers did not apply soap or detergent to Anjou pears, which equates to precisely 50% of the pears not being treated with soap. All pears were rinsed with fresh water.
Wax application may occur on the line. More than two-thirds of the fruit (71%) is treated with a carnauba wax at various concentrations from 2.5 gallons of formulated carnauba pear wax per 55 gallon drum of solution to full concentration of formulated carnauba apple wax. The difference between carnauba apple and pear wax is in the concentration of solids in the formulation. Apple wax has more solids than pear wax.
Fungicide Sprays Online
In all packinghouses, Anjou pears receive a spray of TBZ online. Given the magnitude of losses from postharvest decay (see Table 1), this is not remarkable.
Although Captan is registered for postharvest use on pears, prohibition of this fungicide (or its residue) by other countries and the lack of willingness of the packers to segregate fruit by market destination are reasons for lack of use. An additional reason has been the lack of willingness by packers to have fruit treated with Captan in long-term storage should the domestic market decide it is unwilling to consume Captan-treated fruit.
Small amounts of Anjou pears are treated with an online spray of chlorine.
The new biocontrol fungicides have been tested commercially by a number of packers with varying results. When this is used, it is applied to long-term CA-stored fruit rather than fruit which will be sold immediately.
Antioxidant Sprays Online
Ethoxyquin is the antioxidant registered for use on Anjou pears. It is used to control superficial scald, which is the browning of the skin of the pear following storage. The application of the antioxidant to Anjou pears is either done as an online spray or imbedded into the paper wrap. Less than one quarter (21%) of the packers apply ethoxyquin as an online spray, however this accounts for 45% of all Anjou pears.
Additional Sprays Online
Only a few packers (16%) applied Semperfresh to Anjou pears. Semperfresh is a sucrose ester reputed to affect ripening and reduce scuffing as fruit is packed. Semperfresh was applied to 20% of all Anjou pears packed in 1996.
Handwrapping Anjou Pears
More than 98% of Anjou pears are handwrapped. The rest are tray filled, bagged, or specialty packs.
The paper wrap is available in several formulations. It is available as untreated (white), oil alone, ethoxyquin and oil, copper and oil, copper and ethoxyquin and oil (Super Copper).
The paper wrap can serve to apply an antioxidant and/or as a material to isolate decaying pears. The antioxidants can be ethoxyquin and/or oil. The vast majority of pears (97%) are wrapped with paper containing oil (Figures 7 and 8). Copper is used in some papers in the belief that it will contain any decay that develops in one pear, preventing it from spreading to surrounding pears.
Figure 7. Distribution paper types used when Anjou pears are handwrapped by total volume of fruit.
Figure 8. Distribution of paper types used when Anjou pears are handwrapped by packinghouses.
A Note about the Application of the Antioxidant. The vast majority (92%) of Anjou pears have ethoxyquin applied. It may be applied in a prestorage drench, a line spray, or in the paper (Figure 9). Although more packers apply ethoxyquin in the paper, there is more fruit treated with a line spray than in the paper (49% as a line spray vs. 43%).
Figure 9. Distribution of the application of ethoxyquin by fruit volume.
Table 2. Summary of chemical use on Anjou pears.
Treatment location Chemical % treated* Bin drench TBZ 6.7 Ethoxyquin 6.0 Dump tank Lignosite 68.0 Silicate 19.0 Sulfate 13.0 SOPP 78.6 Chlorine 15.3 Line spray Soap 50.0 Wax 71.0 TBZ 100.0 Ethoxyquin 45.0 Semperfresh 20.0 Paper wrap Plain 2.0 Copper + oil 21.0 Ethoxyquin + oil 7.0 Oil 26.0 Super Copper** 34.0 * % treated of crop volume surveyed. In this case, survey population for Anjou pears was 7,881,847 44-lb. boxes.
** Super Copper contains ethoxyquin, oil, and copper.
Postharvest Chemical Use on Bartlett Pears
Bartlett pears, or 'Williams' as they are also known, are grown in all three states. California ships more Bartletts for fresh consumption than anywhere in the USA (76,163 tons or 3,384,683 45-lb. boxes in 1996) (Figure 10). The total volume of Bartlett pears shipped from the Pacific Northwest from the 1996 crop was less than the 5-year average (2,007,145 vs. 2,445,519 45-lb. boxes, respectively).
Figure 10. Shipment of fresh Bartlett pears by district in the Pacific Northwest.
The marketing season for fresh Bartletts in California is very short, and most packers do not use CA storage. In Oregon and Washington, Bartletts are marketed for up to 6 months and CA is used extensively.
I obtained information from 16 major Bartlett shippers from all three states. They accounted for 65,644 tons or 2,916,439 45-lb. boxes, or 54% of the total crop. The information reported here accounts for Green Bartlett pears, not Red Bartlett or other summer pear varieties. Green Bartlett pears are far more numerous than other varieties.
In the Pacific Northwest (PNW), 39% of the fresh Bartletts of the 5-year crop were stored in CA storage. In 1996, this figure rose to 41% of PNW Bartlett crop, while in California 3.6% of the Bartletts were stored in CA in 1996.
None of the Bartletts were drenched prior to storage in 1996.
Chemicals Used in the Dump Tank
In those packinghouses that participated in this survey, the majority of the fruit was dumped into water with no flotation material or onto a dry line (53% of the fruit). However this was the practice in only 25% of the packinglines.
Lignosite was used as a flotation material by 56% of the packers on 30% of the crop. Sodium sulfate was used by 13% of the packers (15% of the fruit), and sodium silicate was used by 6% of the packers on 2% of the fruit.
When Bartletts are dumped onto a dry belt or into a water system, 52% of the fruit do not have a fungicide added at this point (38% of the packinglines). SOPP is used on 19% of the fruit on 38% of the packinglines. Chlorine is used on 30% of the fruit in 25% of the packinglines.
The intensity of control of postharvest decay in Bartlett pears depends on the marketing season for the crop. When packers are marketing Bartletts immediately after harvest there is little, if any, fungicide applied. All packers reported that they spend time cleaning and sanitizing the packing equipment.
Chemicals Used on the Fruit on the Packingline
Following dumping, the fruit are rinsed with fresh water. None of participants in this survey on Bartlett pears applied an antioxidant to the fruit. Soap or detergent is applied to 23% of the fruit in 38% of the packinglines.
Carnauba wax is applied on 20% of the Bartlett pears in this survey, in 38% of the packinglines. Shellac wax is applied on 5% of the fruit by 6% of the packers, and 75% of the fruit are unwaxed in 56% of the packinglines.
The majority of Bartletts (45%) are not sprayed with a fungicide. TBZ is used on 39% of the fruit in 63% of the packinglines. Chlorine is applied as a line spray on 16% of the fruit in 13% of the packinglines.
Packing Bartlett Pears
Bartletts are either handwrapped or filled into the box without tray, bag, or wrapping. The latter system is called "tight fill" and is practiced by all of the packers in the California Bartlett industry to some extent. Most of the Bartlett pears in this survey are tight filled (56%); the rest of the fruit are handwrapped with untreated paper (44%). There is no antioxidant or copper in the paper used on Bartlett. The paper for the pears that are handwrapped is untreated, either white or Kraft.
Table 3. Summary of chemical use on Bartlett pears.
Treatment location Chemical % treated* Bin drench TBZ 0.0 Ethoxyquin 0.0 Dump tank Lignosite 30.0 Silicate 2.0 Sulfate 15.0 None 53.0 SOPP 19.0 Chlorine 15.3 None 52.0 Line spray Soap 23.0 Wax 25.0 TBZ 39.0 Chlorine 16.0 Paper wrap Untreated 44.0 No paper 56.0 * % treated of crop volume surveyed. In this case, survey population for Bartlett pears was 2,916,439 44 boxes.
Postharvest Chemical Use on Bosc Pears
Bosc pears, or Buerre Bosc as they are also known, are grown mainly in Oregon in the Medford and Hood River Districts (Figure 11). These two districts account for 58% of all Bosc pears grown on the west coast. New Bosc pear plantings have recently been made as far north as Okanogan County in Washington State.
Figure 11. Bosc pear shipments, 1996.
The marketing season for Bosc pears lasts through the end of March in most years. Much of the fruit is stored in CA.
I met with 12 shippers of Bosc pears who accounted for 1,334,747 boxes of pears out of total crop of 3,348,000 (40% of total) in 1996. I am confident that the postharvest chemical practices are typical for the industry.
Half of the fruit (52%) was stored in regular storage with the rest in CA. Five of the 12 shippers marketed Bosc pears for up to 4 to 6 months while the rest marketed up to 9 months. There was no difference in chemical use between these two groups.
Drenching Bosc Pears
See the discussion under "Drenching Anjou Pears" about the pros and cons of drenching pears. Bosc pears are more susceptible to decay organisms than are Anjou pears, so drenching is a very risky proposition. Packers reported that 170,397 boxes of Bosc pears (13% of the total crop) were drenched.
The vast majority (97%) of Bosc pears that were drenched were placed into CA storage. TBZ was used on 13% of the total Bosc crop as a drench; 1.8% of the total crop was drenched with TBZ plus ethoxyquin.
Packing Bosc Pears
Packers who process both Anjou and Bosc pears use the same chemicals on the packingline on both fruits. However, the survey of Bosc packers included a number of packers who do not pack Anjous.
Dump Tank Chemicals
The flotation material of choice is lignosite with 67% of the Bosc packers using it on 69% of all Bosc packed. Sodium sulfate is used by 17% of the packers on 11% of the fruit. Sodium silicate and sodium carbonate are each used by a single packer.
SOPP is added to dump tank flotation materials in 7% of the packinghouses on 89% of the fruit. The rest of the packers use chlorine.
Line Sprays on Bosc Pears
Soap is used by 42% of the packers on 27% of the Bosc pears.
Most of the Bosc pears are not waxed. Wax is used on 42% of the packinglines on 26% of the fruit. Those packers who use wax chose to use a carnauba based wax and add between 5 to 25 gallons of formulated pear wax to a 55 gallon tank of water and spray this on the fruit as it passes over the packingline. One packer uses full strength apple wax on Bosc pears on the packingline.
All packers spray some formulation of TBZ onto Bosc pears on the packingline. In addition, 17% of the packers apply Captan to 9% of the total crop, and another 17% of the packers apply a chlorine spray to 11% of the crop. A biocontrol fungicide was applied to 18% of the Bosc crop.
Semperfresh was applied to 4% of the Bosc crop by 17% of the packers.
Method of Packing Bosc Pears
The majority of Bosc pears (96%) were marketed handwrapped. The most common paper was white (untreated) that was used on 65% of the fruit by 58% of the packers. Paper containing only oil was used on 31% of the fruit by 33% of the packers.
Table 4. Summary of chemical use on Bosc pears.
Treatment location Chemical % treated* Bin drench TBZ 13.0 Ethoxyquin 1.8 Dump tank Lignosite 69.0 Silicate 8.0 Sulfate 11.0 Carbonate 12.0 SOPP 89.0 Chlorine 11.0 Line spray Soap 27.0 Wax 26.0 TBZ 100.0 Captan 9.0 Chlorine 11.0 Biocontrol 18.0 Semperfresh 4.0 Paper wrap Untreated 65.0 Oil 33.0 * % treated of crop volume surveyed. In this case, survey population for Bosc pears was 1,334,747 boxes.
Postharvest Chemical Use on Comice PearsComice pears are grown predominately in the Medford (59%) and Hood River Districts (23%) of Oregon and have achieved wide acceptance as a gift pear. The total volume of Comice pears in 1996 was 209,143 boxes.
I had the opportunity to visit with packers responsible for packing 60% of the Comice pears.
The vast majority of Comice pears were placed into regular atmosphere storage and the marketing season extended up to 6 months with fruit from CA filling in the last part of the season. The fruit were not drenched upon receipt.
Most of the packers used sodium sulfate to float Comice pears (55%); no fungicide was used in the dump tank. Lignosite was used to float the rest of the Comice crop included in this survey; SOPP was included in the dump tanks.
TBZ was used as a line spray on all Comice and there was no antioxidant used.
Fruit were either packed without wrap or with untreated paper.
Summary of Chemical Use
The pear industry of the western USA is dependent upon very few chemicals for the control of postharvest diseases and disorders. These diseases and disorders are both serious and economically important. Growers have invested all their input and effort into this fruit when it goes into storage, and any losses severely affect the bottom line. It has been well established that postharvest losses from both postharvest disease and disorders are economically serious (Kupferman et al.).
Postharvest losses from disorders mainly have been due to the development of storage scald. The only antioxidant registered for use that is effective against storage scald on pears is ethoxyquin. Loss of this chemical would seriously threaten this industry, as it is impossible to sell all pears in a short period of time. An alternative chemical is the oil in the paper, but it is far less effective than ethoxyquin. Low oxygen storage is not as desirable as ethoxyquin since it is not as effective and increases the risk of internal browning and superficial spotting of the skin.
Packers were asked to rate the importance of certain chemicals to their postharvest practices. The precise question asked was: "What would the effect on pear quality and marketing be if ethoxyquin was lost?" You may not have full data; we are seeking your best opinion. Rating 1 = not serious; 3 = moderately serious, and 5 = extremely serious impact on your ability to store and pack pears."
Packers of Anjou pears and Bosc pears rated ethoxyquin very high. The average score for ethoxyquin was 4.5 for packers of Anjou pears and 2.4 for packers of Bosc pears (out of 5).
An important part of the postharvest packing program for pears is the use of flotation materials. When packers were asked to rate the value of each of the flotation materials, lignosite was the most important (Figure 12) in the case of either Anjou or Bosc.
Figure 12. Anjou and Bosc flotation materials rating.
Losses from fungal diseases are the most serious of all postharvest problems in pears. The major fungal disease organisms are Penicillium, Botrytis, Mucor, and Phialophora. Chemicals available for protection against fungal disease include thiabendazole (TBZ), Captan, and biological control agents. Chlorine dioxide, chlorine, and ozone are sporicides used primarily to sanitize the water systems. Hot water and high pressure hot water have been attempted without significant success.
When packers were asked to rate the importance of the various fungicides to their postharvest program, both SOPP and TBZ are considered vitally important (Figure 13).
Figure 13. Decay control chemicals for Anjou and Bosc.
The fungicides provide an essential component in an integrated system to protect pears from decay. They are not extremely effective, and losses from diseases continue to be a large economic problem. Yet, losses would be far more should these chemicals be lost to the industry.
In this survey, packers rated fungicides, flotation materials, pear wrap (4.0 score), and the antioxidant ethoxyquin as essential to any system of control of diseases or disorders at this time. They hold hope for the use of biological controls in the future, but at this time they are not widely used due to lack of efficacy and cost. Semperfresh also is of interest to pear packers, but its use needs to be further defined.
In short, pear packing systems are dependent upon very few chemicals. Should effective alternative strategies prove to be more effective and economical, these new technologies could be adopted. Until then, the entire industry located in the 3 western states needs these chemicals to continue to survive.
Postharvest Practices: Storage Regimes for Anjou Pears
The storage regime for Anjou pears was very consistent between packers. The temperature for Anjou pears was held at 30.5°F for both packed and loose fruit, CA, or regular storage. It was the same whether fruit were stored in regular storage or in CA. The highest storage temperature reported for regular storage of Anjou pears was 32.5°F and the lowest was 29°F. For CA storage of Anjou pears the highest temperature reported was 33.5°F and the lowest was 29°F. The average was 30.5°F.
The CA regime for Anjou pears was to hold the oxygen at 1.72% and not allow the carbon dioxide to rise above 0.7%. The range in oxygen levels reported was from a high of 2.5 to a low of 1%. The range of carbon dioxide was from a high of 1% to a low of 0 (lime).
Postharvest Practices: Storage Regimes for Bosc PearsThe regimes used for Bosc were very close to those for Anjous. The temperature for regular storage Bosc pears was 31.1°F and ranged from a reported high of 31.5°F to a low of 29.5°F.
The temperature of Bosc pears in CA averaged 30.1°F with a range of 29° to 31°F. The oxygen level averaged 1.7% with a range of 1 to 2.25%. Carbon dioxide averaged 0.5% and ranged from a high of 1 to a low of 0 when lime was used.
A Note about These Values. It is important to recognize that the values cited here are reported by management as 'SET POINT' values for temperature, oxygen, and carbon dioxide. Obviously, there is some swing around these values.
Postharvest Practices: Management of Anjou PearsThe vast majority of Anjou pears are packed and stored in CA in cartons with polyliners. Each pear is handwrapped (see the first section of this report). However, many packers handle the packing schedule differently.
Some packers have had success following this regime:
At harvest, pears are often cooled by spreading the bins out in many different cold rooms to remove the field heat, then transferring them into CA or regular storage rooms.
Fruit to be sold between harvest and February is not drenched, but stored in CA or in regular storage, loose in bins. It is packed and sold as needed after being cooled. This is the weakest fruit as identified by the fieldmen. Often it is the last fruit harvested.
Fruit to be sold between February and March is packed in November and stored in cartons in CA.
Fruit to be sold from April to the end of the season is packed in September and October and stored in cartons in CA. Packing for CA storage is often interrupted by the need to pack for immediate export or domestic sales. This can delay the filling of long-term CA rooms. However, the greatest success in the longest-term marketing (early summer) comes from fruit packed immediately after harvest.
Fruit packed after November is not held, but sent to market soon after packing.
It is typical that fruit packed following more than 30 days after harvest is often stored in CA prior to packing, despite the fact that it does not qualify for CA prior to packing. This fruit may be qualified for CA after it has been packed and put back into CA.
Another packer packs up all regular storage fruit by the end of October and then packs for long-term CA. After a room is filled, the oxygen is brought down to less than 5% within 12 hours. All packing is done by Thanksgiving and the first packed is the last to be shipped.
An alternative system is one in which the packer presizes and sorts the fruit, placing the pears into bins again. This is done immediately after harvest. He then segregates it for either CA or regular storage after it has been treated with the antioxidant and fungicide. Fruit is then packed on order. Storage in cartons is limited to 30 days or less.
Another packer will presize fruit for long-term CA storage. Then he will pack through the middle of the season from field run fruit that has been held loose in CA.
How long can Anjou pears be stored in bins? Some packers reported negative experiences when fruit has been held in storage in bins. They report increased shrivel, increased decay, and increased scuffing when the fruit is finally packed.
Other packers have had positive experiences storing Anjou pears in bins until the end of March, most years. Often these packers will have applied a fungicide and antioxidant to the fruit either in the presize process or as a bin drench at harvest. They report a reduction in Gray Mold but an increase in Blue Mold decay over undrenched fruit.
Additional ReadingApel, G. 1993. Chlorine dioxide. Tree Fruit Postharvest Journal 4(1):12-13.
Apel, G. 1993. Chlorine dioxide. Proc. 9th Annual Wash. Tree Fruit Postharvest Conference pp. 88-89.
Apel, G. W. 1989. Dump tank chemicals. Proc. 5th Annual Wash. Tree Fruit Postharvest Conference pp. 41-42.
Apel, G. 1993. Flotation materials for pears. Tree Fruit Postharvest Journal 4(1):19-21.
Brandli, G. 1996. Postharvest disease control: New technology. Proc. 12th Annual Wash. Tree Fruit Postharvest Conference pp. 335-38.
Chen, P. M. and D. M. Varga. 1993. Improved ethoxyquin treatment for control of superficial scald on Anjou pears. Tree Fruit Postharvest Journal 4(2):27-30.
Chen, P. M. and D. M. Varga. 1993. Reevaluating DPA postharvest drenching of Anjou pears to control superficial scald disorder. Tree Fruit Postharvest Journal 4(2):35-38.
Chen, P. M. and D. M. Varga. 1993. Control of superficial scald of Anjou pears by short-term hyper-low oxygen stress as influenced by carbon dioxide concentration. Tree Fruit Postharvest Journal 4(2):53-57.
Chen, P. M. and D. M. Varga. 1997. CA regimes for control of superficial scald of d'Anjou pear. Proc. 13th Annual Wash. Tree Fruit Postharvest Conference pp. 17-26.
Jeffers, S. N. and T. R. Hankinson. 1995. Biological control of postharvest diseases of apples and pears: Preliminary results from the 1994 Bio-save field trial program. Proc. 11th Annual Wash. Tree Fruit Postharvest Conference pp. 37-40.
Jeffers, S. N., T. S. Wright, R. M. Gorrell and R. G. Roberts. 1993. Control of postharvest diseases of apples and pears with biological control agents. Proc. 9th Annual Wash. Tree Fruit Postharvest Conference pp. 94-96.
Kupferman, E. M. 1989. Handling d'Anjou pears to avoid storage disorders. Proc. 5th Annual Wash. Tree Fruit Postharvest Conference pp. 24-25.
Kupferman, E. M. 1992. Update on the use of chlorine. Tree Fruit Postharvest Journal 3(20:12.
Kupferman, E. M. 1994. Anjou pear quality. II. Postharvest practices. Tree Fruit Postharvest Journal 5(1):11-13.
Kupferman, E. M. 1995. Postharvest handling of Anjou pears. Tree Fruit Postharvest Journal 6(2):3-8.
Kupferman, E. M. 1995. Postharvest handling Anjou pears. Proc. 11th Annual Wash. Tree Fruit Postharvest Conference pp. 33-36.
Kupferman, E. M. 1997. Observations on storage regimes for apples and pears, 1997. Tree Fruit Postharvest Journal 8(3):3-5.
Kupferman, E. M. and D. Burkhart. 1992. Results of a survey to determine reasons for postharvest cullage of the 1990 Anjou pear crop. Proc. 8th Annual Wash. Tree Fruit Postharvest Conference pp. 81-82.
Kupferman, E. M. and H. Waelti, eds. 1993. Postharvest diseases and disorders of apples and pears. Tree Fruit Postharvest Journal 4(1):3-4.
Kupferman, E. M. and H. Waelti, eds. 1993. Postharvest practices to minimize decay in pears. Tree Fruit Postharvest Journal 4(1):10-11.
Kupferman, E. M., R. Spotts and D. Sugar. 1995. Practices to reduce postharvest pear diseases. Tree Fruit Postharvest Journal 6(2):18-23.
Kupferman, E.M., K. Miller, L. Kutch and D. Burkhart. 1992. Reducing postharvest losses in Anjou pears: A report on the 1991 crop. Tree Fruit Postharvest Journal 3(4):18-23.
Lennox, C. and R. Spotts. 1997. Botrytis gray mold as a postharvest pathogen in d'Anjou pear. Proc. 13th Annual Wash. Tree Fruit Postharvest Conference pp. 93-95.
Sanderson, P. G. 1993. Blue mold. Proc. 9th Annual Wash. Tree Fruit Postharvest Conference p. 92.
Sanderson, P. G. and K. Miller. 1997. Fungicidal drenches for control of postharvest decay in d'Anjou. Proc. 13th Annual Wash. Tree Fruit Postharvest Conference pp. 89-91.
Sanderson, P. G. and R. A. Spotts. 1995. Blue mold: An expanded concept. Tree Fruit Postharvest Journal 6(2):15-17.
Sanderson, P. G. and R. A. Spotts. 1992. Blue mold: An expanded concept. Proc. 8th Annual Wash. Tree Fruit Postharvest Conference pp. 86-87.
Smith, M. 1997. Chemical safety: What you can mix and what you can't. Proc. 13th Annual Wash. Tree Fruit Postharvest Conference pp. 99-101.
Spotts, R. A. 1989. Mucor rot and blue mold. Proc. 5th Annual Wash. Tree Fruit Postharvest Conference pp. 35-36.
Spotts, R. A. 1992. Additional studies with ozone for decay control. Proc. 8th Annual Wash. Tree Fruit Postharvest Conference p. 85.
Spotts, R. A. and L. A. Cervantes. 1993. Filtration to remove spores of Penicillium expansum from water in pome fruit packinghouses. Tree Fruit Postharvest Journal 4(1):16-18.
Spotts, R. A. and L. A. Cervantes. 1993. Filtration for removal of spores of Penicillium expansum from water in pome fruit packinghouses. Proc. 9th Annual Wash. Tree Fruit Postharvest Conference pp. 90-91.
Spotts, R., R. Roberts, H. W. Ewart, D. Sugar, G. Apel, M. Willett and E. M. Kupferman, eds. 1992. Management practices to minimize postharvest decay of apples and pears. Tree Fruit Postharvest Journal 3(2):5-8.
Spotts, R., R. Roberts, H. W. Ewart, D. Sugar, G. Apel, M. Willett and E. M. Kupferman, eds. 1992. Flotation materials for pears. Tree Fruit Postharvest Journal 3(2):9-11.
Spotts, R., R. Roberts, H. W. Ewart, D. Sugar, G. Apel, M. Willett and E. M. Kupferman, eds. 1992. Residue tolerances for postharvest chemicals on apples, pears and cherries. Tree Fruit Postharvest Journal 3(2):15-16.
Sugar, D. 1989. Flotation materials for pears. Proc. 5th Annual Wash. Tree Fruit Postharvest Conference pp. 19-22.
Sugar, D. 1989. Experiences in handling and packing Bosc and red pears. Proc. 5th Annual Wash. Tree Fruit Postharvest Conference pp. 22-23.
Sugar, D. 1992. Experiences in handling and packing Bosc and red pears. Tree Fruit Postharvest Journal 3(3):7-9.
Sugar, D. 1994. Reducing postharvest decay in pears through integrated management. Proc. 10th Annual Wash. Tree Fruit Postharvest Conference p. 60.
Sugar, D. 1997. Control of postharvest decay with chemical and biological fungicides. Proc. 13th Annual Wash. Tree Fruit Postharvest Conference pp. 97-98.
Sugar, D. and R. Spotts. 1995. Preharvest strategies to reduce postharvest pear decay. Tree Fruit Postharvest Journal 6(2):13-14.
Tukey, B. 1993. Overview of ozone use at Snokist Growers. Tree Fruit Postharvest Journal 4(1):14-15.
Tukey, B. 1993. Ozone: An overview of its use at Snokist Growers. Proc. 9th Annual Wash. Tree Fruit Postharvest Conference p. 93.
Willett, M. and E. M. Kupferman, eds. 1991. Management practices to minimize postharvest decay of apples and pears. Tree Fruit Postharvest Journal 2(2):5-8.
Willett, M. and E. M. Kupferman, eds. 1991. Flotation materials for pears. Tree Fruit Postharvest Journal 2(2):9-11.
Willett, M. and E. M. Kupferman, eds. 1991. Residue tolerances for postharvest chemicals on apples, pears and cherries. Tree Fruit Postharvest Journal 2(2):14-15.
Dr. Eugene Kupferman, Postharvest Specialist
WSU Tree Fruit Research and Extension Center
1100 N. Western Ave., Wenatchee, WA 98801
Tree Fruit Postharvest Journal 9(1):3-24