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Organic Pear Production

  1. 1. ORGANIC PEAR PRODUCTION HORTICULTURE PRODUCTION GUIDE Abstract : This introduction to commercial organic pear production covers pear diseases, disease-resistant cultivars, insect and mite pests and their treatment, Asian pears, and marketing. Electronic and print resources are provided for further research.By Martin Guerena and Holly Born ticles, and websites (seeNCAT Agriculture Specialists the Further ResourcesUpdated by Tracy Mumma section at the end of thisApril 2003 document). For cultural information more spe-Introduction cific to organic produc- © 2003 tion (organic fertiliza-In most of the U.S., pears may be the easiest of tion, organic weed control, etc.) requestthe tree fruits to produce organically or with ATTRA’s Overview of Organic Fruit Production.minimal spraying. Pears’ fertility requirementsare not high, they are adapted to a wide range of Pears have most of the same pest and diseaseclimates and soils, and they have fewer pest problems that apples have, but usually to a con-problems than other tree fruits. siderably lesser degree. ATTRA’s Organic and Low-Spray Apple Production identifies pests andStandard cultural considerations—such as prun- suggests organic remedies that are just as ap-ing, choice of rootstock, planting, spacing, and propriate to pears; therefore, most of these prob-thinning—are generally the same for organic and lems will not be discussed further in this publi-conventional growers. For this type of cultural cation. However, because of its importance andinformation consult your county or state Coop- prevalence on pears, fireblight will be consid-erative Extension Service and/or find the infor- ered in more depth. Other pests and diseasesmation in any number of orcharding texts, ar- peculiar or especially troublesome to pears will also be discussed. Related ATTRA Publications• Overview of Organic Fruit Production Table of Contents• Postharvest Handling of Fruits & Veg- Introduction ........................................... 1 etables Diseases .................................................. 2• Insect IPM in Apples: Kaolin Clay Insect and Mite Pests............................ 5• Farmscaping to Enhance Biological Con- Asian Pears ............................................. 6 trol Economics and Marketing .................. 7• Biointensive Integrated Pest Management (IPM) References .............................................. 8• Organic & Low-spray Apple Production Additional Resources ........................... 9• Organic Grape Production Appendix: Fireblight, Disease• Organic / Low Spray Peach Production Resistance, and the Disease• Low Spray & Organic Plum Production Triangle ................................................... 9ATTRA is the national sustainable agriculture information service, operated by the National Centerfor Appropriate Technology through a grant from the Rural Business-Cooperative Service, U.S.Department of Agriculture. These organizations do not recommend or endorse products,companies, or individuals. NCAT has offices in Fayetteville, Arkansas (P.O. Box 3657, Fayetteville,AR 72702), Butte, Montana, and Davis, California.
  2. 2. Comparing a Pair of Pears European pears Asian pears Scientific names Pyrus communis Pyrus ussuriensis P. serotina P. bretschneideri Common cultivars Bartlett, Bosc, D’Anjou, Seckel, 20th Century, Shinseiki, Magness, Maxine, Moonglow, Korean Giant, Shinko, Comice Chojuro, Niitaka Texture and flavor Buttery smooth and sweet. Crisp. Flavors vary widely, including bland, sweet, sweet-tart, pineapple-like, and more. Color Green to yellow, though Green, yellow to golden, russetted types are dull bronze, russetted bronze, and and there are a few red types. many types with white lenticels (spots). Shape Pyriform (i.e., round & bulb- Most cultivars are round. like on the calyx end, Some are misshapenly narrowing to a slender neck at round. A few are stem end). somewhat pyriform. Harvest and postharvest Harvest before fully ripe. Allow to tree-ripen. Ready Allow to ripen (cure) at room to consume or sell. temp. Buyer usually does curing. Pests and diseases Same as for Asian (see text). Same as for European (see text).Diseases wither and turn black or brownish black, as ifFireblight scorched. Most branch tips, once infected, wilt rapidly, taking on the characteristic shape of aFireblight, caused by the bacterium Erwinia “shepherd’s crook.” The bacteria gain entry toamylovora, is one of the most serious and eco- the tree through blossoms or lush new growthnomically damaging diseases of pears. Occur- and, once inside, begin to work toward the roots.ring throughout the pear’s range, it is particu- If the disease spreads unchecked to the trunk andlarly troublesome in the humid eastern United roots, it can kill the tree; however, in resistantStates. Infection is triggered by heat and mois- varieties the bacteria rarely invade beyond youngture, and can spread rapidly—even within a wood. Under the bark, the bacteria form a can-matter of hours. It can be transmitted by bees, ker where they will survive the winter, only toaphids, psylla, or other insects, and can also be infect more trees the next year. If on a warm dayspread by blowing wind and rain. Pruning can you see pustules on a tree, oozing an orange-be another source of infection. Affected branches brown liquid, you are looking at fireblight (1).PAGE 2 //ORGANIC PEAR PRODUCTION
  3. 3. Choosing fireblight-resistant pear cultivars is a goodstart to managing fireblight, but it is by no meansa panacea (see the Appendix “Fireblight, DiseaseResistance, and the Disease Triangle”). There areseveral European-type pears with a comparativelyhigh level of fireblight resistance (Ayres, Magness,Potomac, Warren, Maxine, Moon Glow, Tyson,Honeysweet, Kieffer, Blake’s Pride, Shenandoahetc.) that are adapted to most of the contiguousUnited States. Clapps, Bartlett, Comice, Anjou,Bosc, and most other cultivars that are not ex-pressly described as “fireblight resistant” in anursery catalog should be considered susceptible. Using these two substances together can re- duce the amount of streptomycin sprayed each year, which may help to protect the antibiotic’s effec-tiveness. By itself, BlightBan can provide up to 50% suppression, but not control. It can- not be used in combination with copper sprays. The biocontrol bacteria live only about three weeks in the orchard, and there is no carry-over from year to year. BlightBan is distributed by Nufarm USA (7). Note that it is not registered for use in all states.
  4. 4. mum temperatures, rainfall, and stage of blos- vars in particular. Because the presence of blos-som development, and the program predicts in- som-blast bacteria allows ice crystals to form atfection events and symptom development for higher-than-normal temperatures, the diseasemost phases of fireblight. Further information increases the incidence of freeze damage duringon the program is available at the USDA’s cold wet weather. Asian pears are especially af-Kearneysville, West Virginia, web site <http:// fected because their early bloom makes>. In the more susceptible to frost injury (8). Of the Asian-Pacific Northwest the similar but freely-distrib- pear cultivars mentioned above, Shinko and Yauted Cougarblite Model <http:// Li are moderately resistant to P.> is more oftenused to help time spraying, and elsewhere other Controlling this disease is difficult because itsdegree-hour models from local sources may be occurrence is widespread on many plant speciesmore appropriate. and not easily predicted; once symptoms appear, control efforts are too late. Protecting orchardsOnce fireblight infection has occurred, there is from frost damage can limit injury. An earlyno spray or other treatment, beyond quickly cut- application of BlightBan® A506 can help reduceting out newly infected limbs, that will minimize frost damage potential by excluding the ice-damage. However, infection has almost certainly nucleating bacteria. In California, the applica-extended beyond what the grower sees; there- tion of fixed copper at the green-tip stage fol-fore, it is all too easy to spread the disease by lowed by streptomycin at early bloom has pro-trying to prune it out during the growing sea- vided reasonable control. This treatment has alsoson. If you do cut during the growing season, been used in Oregon, where cool wet weatherremove all blighted twigs, branches, and cankers makes blossom blast a particular problem in pearat least 8 inches—some sources recommend 12— production. Streptomycin or terramycin appliedbelow the last point of visible infection, and burn at early bloom to control fire blight also help tothem. After each cut, the shears can be sterilized control blossom blast, although the most effec-in a strong bleach or Lysol® solution (1 part tive timing of application for the two diseases ishousehold bleach or Lysol to 4 parts water) to somewhat avoid transmitting the disease from onebranch to another, although there is some dis- Pear scabagreement about the effectiveness of disinfection.Lysol is less corrosive than bleach to the metal Pear scab (Venturia pirina), a fungal diseaseparts of the pruners. Some have found it more closely related to apple scab, is neither as com-convenient to use a spray can of Lysol disinfec- mon nor as economically important on pears astant carried in an apron rather than a plastic hol- apple scab is on apples. Nevertheless, it can causester or glass jar with a liquid solution. economic damage by marring the appearance of the fruit. Pear scab causes lesions on leaves,During the winter, when the temperature ren- shoots, and fruit, and—unlike apple scab—in-ders the bacteria inactive, pruning out fireblight- fects twigs, where it can overwinter. Pear culti-infected wood can proceed without sterilization vars differ in their susceptibility to scab. Organicof pruning tools, and need not extend as far be- control is identical to that for apple scab (9), usu-low the visible canker. ally consisting of treatment with sulfur, lime-sul- fur, or Bordeaux mixture. See ATTRA’s OrganicBlossom blast and Low-spray Apple Production for details, includ- ing the use of the Mills Table to predict infectionAnother bacterial disease, blossom blast (causal periods.organism: Pseudomonas syringae, not to be con-fused with Psedomonas fluorescens discussed Other diseasesabove), may afflict pears, usually as a blossomblight resulting in reduced fruit set. It can also Two foliar diseases, fabraea leaf spot (Fabraeacause twig dieback and bark cankers, and may maculata) and mycosphaerella leaf spotlead to severe wood damage of Asian-pear culti- (Mycosphaerella pyri), are usually no problem inPAGE 4 //ORGANIC PEAR PRODUCTION
  5. 5. sprayed orchards but can reach damaging levels control has made organic pear production viablein unsprayed ones (9). Susceptible cultivars, for the first time in states like Michigan (10). Thewhich include nearly all European pears, can be psylla also has a number of natural enemies suchdefoliated, resulting in reduced buds and as predatory flies, minute pirate bugs, and lacew-dwarfed or—if the fruit itself is infected—unmar- ing larvae. In organic orchards parasites andketable fruit. Sprays for pear scab, such as Bor- predators can help control psylla below economi-deaux mixture, will generally control these two cally damaging levels, especially when combinedmaladies as well. Also, Surround™, a kaolin- with a program of oil treatments (11).clay-based insect repellant, is registered and la-beled for suppression of fabraea leaf spot. More True bugsinformation on Surround is available in ATTRA’sInsect IPM in Apples: Kaolin Clay. Stink bugs, tarnished plant bug, and other true bugs (insects in the order Hemiptera) will readilyInsect and Mite Pests feed on pears throughout the growing season. Early feeding damage may result in a pucker orMany of the same pests that affect apples also dimple in the fruit. Mid- and late-season feed-prey on pears, although often to a lesser degree. ing often results in the development of so-calledMore information on dealing with these pests can “stone cells” immediately beneath the feedingbe found in ATTRA’s Organic and Low-Spray site. These stone cells are very hard and can se-Apple Production. Some of the pests that particu- riously compromise the marketability of affectedlarly affect pears are discussed below. Proper fruit.pest identification and orchard scouting are keyto implementing successful IPM programs. Some fruit and nut growers reduce true-bugATTRA’s Biointensive Integrated Pest Management damage by maintaining unmown leguminous(IPM) publication provides additional informa- trap crops (clovers, vetches, peas, etc.) near thetion. orchard (12). Unmown areas and cover crops can also serve as habitat for predator insects—Pear psylla for more information, see the ATTRA publica- tion Farmscaping to Enhance Biological Control.The pear psylla (Cacopsylla pyricola), an aphid- Surround™ is labeled for suppression of stink-like insect whose only host is the pear, is the bugs and lygus bugs in pears. Also, some of thecrop’s most significant insect pest. In conjunc- relatively new biological insecticides derivedtion with fireblight, pear psylla is largely respon- from the seeds of the neem tree are effectivesible for the decline in Eastern pear production. against true bugs on fruit crops. For example,The honeydew left by the psylla damages the Aza-Direct™, which is listed by the Organicfruit by supporting growth of sooty mold and Materials Review Institute (OMRI) for use in or-causing a black russeting; these two effects ac- ganic production, is labeled for use on all pomecount for most of the economic damage caused fruits for the control of weevils, thrips, true bugs,by the psylla. It is also an important vector of leafhoppers, aphids, leafrollers, cutworms, flies,fireblight and “pear decline disease,” and can and mites. Aza-Direct is produced by Gowanweaken trees in areas of heavy infection. Company (13).Although the psylla develops resistance to insec- Mitesticides, it can usually be controlled either withdormant oil sprays or with sulfur sprays (but not In high enough numbers, pearleaf blister mitesa combination of the two, which damages plants.) (Phytoptus pyri) and pear rust mites (EpitrimerusInsecticidal soap can reduce active populations pyri) can reduce the photosynthetic efficiency ofduring the growing season. Fortunately, the re- leaves and cause russeting on fruit. Both speciescently-introduced Surround™ (discussed above will likely be more troublesome in dusty condi-under Other diseases) is effective against pear tions, as the dust interferes with their naturalpsylla. In fact, use of Surround for pear psylla predators. These predators—including green //ORGANIC PEAR PRODUCTION PAGE 5
  6. 6. lacewings, predatory mites, and various species Peshastin Creek Growers Areawideof ladybird beetles, as well as bigeyed bugs, Organic Projectminute pirate bugs, and predatory thrips—will In a Washington valley, twelve family-ownedusually control mite outbreaks if they are not dis- orchards with approximately 300 acres ofrupted by dust or pesticides. Orchard monitor- pears have joined together to establishing can help establish whether adequate num- an areawide insect pest managementbers of beneficial insects are present. If not, hor- program based on the use of organic insect-ticultural oils sprayed during the dormant sea- control tactics.son can suppress mite eggs through suffocation. Dennis Nicholson and Rich MillerNeither horticultural oils nor other materials Co-Chairpersonsapproved for organic production provide eco- P.O. Box 55nomic control of damaging populations. Peshastin, WA 98847 (509)548-4207Another pest that contributes to poor yields and nichorch@rightathome.comsmaller fruit is the spider mite. Dormant horti- oils and insecticidal soaps can both help pearent/pcg%20home%20page.htmcontrol spider mite outbreaks. Neem-based bio-logical insecticides are also labeled for control- shape, color, and taste. Only about a dozen vari-ling mites on pears. European-pear cultivars are eties are commonly grown in U.S. commercialmore sensitive to mite feeding than Asian pears, orchards.and any pear that is drought-stressed will bemore susceptible to mite damage (14). Asian pears are slightly less cold-hardy than Eu- ropean types; they may suffer tissue damage atOther insects temperatures below –10° F but are generally hardy to –20°, making them best adapted toOther insect pests that may affect pears include USDA climatic zones 5–9. Most Asian pearscodling moth, apple maggot, scale, and plum bloom slightly earlier than their European coun-curculio. These insects are covered in ATTRA’s terparts and may lose some blooms or buds toOrganic and Low-spray Apple Production publica- freezing in areas with a highly variable springtion. The pear slug (actually a sawfly larva) climate.causes leaf damage; it can be controlled with aforceful stream of water, soap, or wood ashes. Culture of Asian pears is similar to that of Euro-The leafroller complex—including tufted apple pean types, but not identical. One significantbud moth, variegated leafroller, and redbanded difference is the common tendency for many ofleafrollers—represents another potential, but the Asian types to set too heavy a fruit crop,comparatively minor, pear pest problem. Mat- which requires hand thinning of young fruit sooning disruption tools that are effective for some after bloom. Shinko, a popular cultivar becauseleafrollers are being developed. In addition, there of its high fruit quality and fireblight resistance,are biological insecticides labeled for control of is especially prone to this problem. If not prop-leafhoppers, aphids, and leafrollers, among other erly thinned, Shinko and any other heavy-bear-pests. ing Asian pear cultivar will not be able to prop- erly mature such a load. Fruit size and qualityAsian Pears will suffer. On the other hand, thinning to pro- mote fruit size may result in reduced yield perBecause they are relatively new to much of the acre compared to European pear varieties.United States, Asian pears deserve some addi-tional comment. A crisp, juicy fruit, Asian pears Another difference between Asian and Europeanare also known as Oriental pears, nashi, sand pears is that Asian pears ripen on the tree—theypears, apple pears, or salad pears. The more than do not have to be picked and then cured like1,000 varieties of Asian pear range widely in European pears. This is an advantage for mostPAGE 6 //ORGANIC PEAR PRODUCTION
  7. 7. growers, especially growers who are retailing based on these factors, and the premium thatdirect to consumers. The fruit can be tree rip- organic growers can expect to receive for theirened and is ready to eat when picked, or can be product is unpredictable at best.held in cold storage. You do not have to educatethe buyer about curing, as you might with Euro- The market for pears is weaker than it could be,pean pears. largely because of consumers’ unfamiliarity with the different types of pears and how to use them.It is important to note that the delicate fruit of One survey showed that Bartletts and wintermany Asian-pear varieties must be carefully pears were consumed by no more than half ofhandled during and after harvest to minimize America’s households, and then only occasion-bruising, punctures, and roller marks. The skin ally. A market study funded by the Pear Bureauof Asian pears discolors quickly following rough showed that only 3 out of 10 people have triedhandling, making careful picking and packag- d’Anjou pears, and 2 out of 10 have tried a necessity, and mechanical handling risky. One of the obstacles limiting pear consumptionTo prevent damage to Asian pears, it may be best is that many consumers do not know how toto pack them into padded boxes or trays in the ripen them. Providing information on ripeningfield where they are picked. may help increase sales (though the Pear Bureau study also found that most people preferred toMore information on Asian pears can be found buy pears already ripened). A substantial per-in the sources provided in the References and centage of purchases are impulse buys, so ap-Further Resources sections. pearance is critical. Many appearance problems come from fruit being handled by retail employ- ees and consumers. Pears should be handledEconomics and Marketing gently, no matter what stage of ripeness they have reached. Rough handling causes brownWorldwide, China is by far the world’s largest marks on the skin that may not appear until thepear-producing country, followed by Italy. The fruit has begun to ripen, and will decrease cus-United States is the third-largest pear producer tomer appeal. Sources of consumer, food-service,in the world. Export markets are important for and other trade-education materials related toU.S. producers—more than 30% of the U.S. fresh European pears are available from the Pear Bu-pear crop is shipped to foreign markets (15). At reau Northwest (17).one time pears were grown commercially on alarge scale throughout the United States. How- The market for Asian pears is mixed. Until 1995ever, because of the prevalence of fireblight in or so, the wholesale market for Asian pears wasthe humid eastern and southern states, most pear quite open and prices were high, particularly onproduction has been relocated to the drier areas the West Coast and in cities with large Asian-of the Pacific Northwest. More than 95% of the American populations. But Asian pears havepears produced in the U.S. are grown in Wash- been heavily planted in California for more thanington, Oregon, and Northern California (16). 20 years, and those orchards are now mature andBartletts remain the most popular pear variety bearing, more than meeting local demand andgrown commercially in the U.S., outnumbering causing price drops in some areas.all other species combined. On the other hand, outside of California, AsianBartlett pear production has been declining pear growers that serve a retail clientele—espe-slightly since 2000, resulting in higher prices for cially a local Asian-American population—reportproducers who continue to grow them (15). In brisk sales and good prices from locations acrossgeneral, pear prices tend to fluctuate based on the country (3, 4). Offering taste sampling of fruit,crop size—which can be highly variable on ac- where practical and allowed by local health regu-count of weather and fruit set rates—and on the lations, is probably a good idea for building mar-number of growers producing pears in a given kets, since so many Americans are still unfamil-year. Fluctuation in the organic market is also iar with Asian pears. //ORGANIC PEAR PRODUCTION PAGE 7
  8. 8. Asian pears are breaking out of their niche to join 10) Elkins, R.B., R. A. Van Steenwyk, L. G.the mainstream market, and may represent an Varela, and C. Pickel. 2001. UCopportunity for producers as market awareness IPM Pest Management Guidelines: Pearand demand continue to grow. Psylla. UC DANR Publication 3339. Accessed August 2002. <http://References r603301111.html>.1) Agrios, G. 1978. Plant Pathology. Aca- demic Press, New York, NY. p. 457–463. 11) Anon. 2002. Organic pears are a viable opportunity for Michigan growers. IPM2) Hall-Beyer, Bart, and Jean Richard. 1983. Report. Spring. p. 1. Accessed August Ecological Fruit Production in the North. 2002 at < Jean Richard Publishing Co., Trois-Rivieres, ipm/ipmrptv8n1.htm>. Quebec, Canada. p. 33–34. 12) Anon. 1999. Pea patch diverts stinkbugs.3) Jones, Terry, and Ed Fackler. 1995. Asian Common Ground. Autumn. p. 4. pears—A past & future in Kentucky. Pomona. Fall. p. 31–35. 13) Gowan Company P.O. Box 55694) Ames, Guy. 2000. Personal communica- Yuma, AZ 85366-5569 tion. 1-800-883-1844 ext. 2 Anon. 2000. The National List of Allowed and Prohibited Substances Description of 14) University of California Statewide Regulations General Requirements. Ac- Integrated Pest Management Project. cessed August 2002. <http:// 1991. Integrated Pest Management for Apples & Pears. University of California FinalRule.html>. Division of Agriculture and Natural Resources. Publication 3340. Oakland,6) Steiner, Paul W. 1995. Maryblyt beats CA. p. 116. fire blight. American Fruit Grower. February. p. 30–31. 15) Perez, Agnes. 2001. Smaller 2001 U.S. Pear Crop to Boost Prices. Agricultural7) Nufarm USA Corporate Headquarters O u t look. November 2001. p.4. 150 Harvest Drive, Suite 200 Burr Ridge, IL 60527 16) Foreign Agricultural Service. 1999. World 630-455-2000 Fax: 866-241-0612 Pear Situation. FAS Online. Accessed July 2002. < Elkins, R.B., and W. D. Gubler. 2001. circular/1999/99-04/pear.htm>. Plant Pathology, UC IPM Pest Man- agement Guidelines: Pear. UC DANR 17) Pear Bureau Northwest Publication 3339. Accessed August 2002. 4382 SE International Way Ste. A < Milwaukie, OR 97222-4635 r603100111.html>. 503-652-9720 Jones, Alan, and Turner B. Sutton. 1996. Diseases of Tree Fruits in the East. NCR 45. Michigan State University, East Lansing, MI. p. 22–23.PAGE 8 //ORGANIC PEAR PRODUCTION
  9. 9. The occurrence of disease—any disease on anyplant or animal—is dependent on three factors:1) a susceptible host; 2) the presence of the dis-ease-causing pathogen; and 3) a suitable envi-ronment for infection and disease development(the “disease triangle;” see Figure 1). This factis very important to understanding fireblight in-cidence in pear orchards, especially in terms ofmanaging this potentially devastating disease indifferent parts of the country.
  10. 10. resistant,” he or she is speaking in relative terms. which is especially prone to infection and seemsUsually we read or hear something like “some- to provide the disease its fastest entry into thewhat resistant,” “very resistant,” “moderately re- wood.sistant,” “slightly susceptible,” etc. To furthercomplicate matters, different researchers use dif- Another practice that can be adjusted to alter theferent rating scales to describe resistance/suscep- orchard environment is pruning, which cantibility—there is no agreed-upon standard. For “open up” a tree to allow more rapid drying ofexample, some published studies rely on a “1 to plant tissues and thus prevent disease. However,10” scale, which is usually based on a visual esti- a grower in a different situation might need tomate of damage, while others may use more ab- reduce pruning in order to avoid fostering the lushsolute measurements, such as the centimeters of shoot growth (which is more susceptible toshoot tissue affected by fireblight. fireblight) that usually follows heavy pruning.Regardless of the failings of the various rating There is considerable interplay, of course, be-systems, the phenomenon of differential resis- tween the faces of the disease triangle. It is espe-tance/susceptibility is real—pear cultivars vary cially important to understand that given highgreatly in their reaction to the presence of Erwinia levels of inoculum and the proper environmen-amylovora. Some cultivars, such as Magness and tal conditions, medium levels of varietal resis-Shinko, will only rarely suffer any fireblight tance can be overcome. For example, Shin-Li—strikes, and, if they do, the blight will rarely in- released by the University of California astrude into any wood older than one year. In con- “fireblight resistant”—is relatively resistant intrast, when all three factors of the disease triangle the climate of California, but can suffer severeconspire, fireblight can kill even some older trees fireblight infection in the Southeast if not ad-of susceptible European cultivars in a single year. equately protected by spraying. If you plant Bartlett in South Carolina, for another example,The second face of the triangle, presence of the and don’t spray, you can watch the disease tri-pathogen, is the one that seems to prompt most angle imitate the Bermuda Triangle, as your treesof our efforts as growers. When we spray cop- disappear one-by-one and year-by-year.per, Blight Ban™, or one of the antibiotics, weare trying to reduce or exclude (in the case ofBlight Ban) the pathogen from potential infec- By Martin Guerena and Holly Borntion sites. There is also a geographic component NCAT Agriculture Specialiststo this part of the triangle, as E. amylovora is much Updated by Tracy Mummaless prevalent in some parts of the world than inothers. Edited by Richard Earles Formatted by Cynthia ArnoldThe third face of the triangle—an environmentconducive to the disease—is also related to ge- April 2003ography, mostly by climate. Where the climateis warm and wet, expecially in the spring,fireblight infection and development are favored.The more arid parts of the western U.S. are notnearly as prone to fireblight problems as most of The electronic version of Organic Pear Productionthe East. But these large climatic and geographic is located at: HTMLfeatures are not the only components of a dis- or disease-suppressive environ- PDFment—the orchardist can manipulate parts of the micro-environment to help suppress dis-ease development. For example, reducing fer- IP167tilization can limit fast-growing succulent tissue,PAGE 10 //ORGANIC PEAR PRODUCTION