Organic Pear Production

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 (see
NCAT Agriculture Specialists the Further Resources
Updated by Tracy Mumma section at the end of this
April 2003 document). For cultural
information more spe-
Introduction cific to organic produc-
©WWW.clipart.com 2003
tion (organic fertiliza-
In most of the U.S., pears may be the easiest of tion, organic weed control, etc.) request
the tree fruits to produce organically or with ATTRA’s Overview of Organic Fruit Production.
minimal spraying. Pears’ fertility requirements
are not high, they are adapted to a wide range of Pears have most of the same pest and disease
climates 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 and
Standard 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 and
information 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 diseases
mation 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 ................................................... 9
ATTRA is the national sustainable agriculture information service, operated by the National Center
for 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. 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 if
Fireblight scorched. Most branch tips, once infected, wilt
rapidly, taking on the characteristic shape of a
Fireblight, caused by the bacterium Erwinia “shepherd’s crook.” The bacteria gain entry to
amylovora, is one of the most serious and eco- the tree through blossoms or lush new growth
nomically 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 and
larly troublesome in the humid eastern United roots, it can kill the tree; however, in resistant
States. Infection is triggered by heat and mois- varieties the bacteria rarely invade beyond young
ture, 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 to
aphids, psylla, or other insects, and can also be infect more trees the next year. If on a warm day
spread 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. Choosing fireblight-resistant pear cultivars is a good
start to managing fireblight, but it is by no means
a panacea (see the Appendix “Fireblight, Disease
Resistance, and the Disease Triangle”). There are
several European-type pears with a comparatively
high level of fireblight resistance (Ayres, Magness,
Potomac, Warren, Maxine, Moon Glow, Tyson,
Honeysweet, Kieffer, Blake’s Pride, Shenandoah
etc.) that are adapted to most of the contiguous
United States. Clapps, Bartlett, Comice, Anjou,
Bosc, and most other cultivars that are not ex-
pressly described as “fireblight resistant” in a
nursery 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. 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 at
fection events and symptom development for higher-than-normal temperatures, the disease
most phases of fireblight. Further information increases the incidence of freeze damage during
on 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 them
afrsweb.usda.gov/fireblight/fb8.htm>. In the more susceptible to frost injury (8). Of the Asian-
Pacific Northwest the similar but freely-distrib- pear cultivars mentioned above, Shinko and Ya
uted Cougarblite Model <http:// Li are moderately resistant to P. syringae.
www.ncw.wsu.edu/models.htm> is more often
used to help time spraying, and elsewhere other Controlling this disease is difficult because its
degree-hour models from local sources may be occurrence is widespread on many plant species
more appropriate. and not easily predicted; once symptoms appear,
control efforts are too late. Protecting orchards
Once fireblight infection has occurred, there is from frost damage can limit injury. An early
no spray or other treatment, beyond quickly cut- application of BlightBan® A506 can help reduce
ting 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 also
son. If you do cut during the growing season, been used in Oregon, where cool wet weather
remove all blighted twigs, branches, and cankers makes blossom blast a particular problem in pear
at least 8 inches—some sources recommend 12— production. Streptomycin or terramycin applied
below the last point of visible infection, and burn at early bloom to control fire blight also help to
them. 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 is
household bleach or Lysol to 4 parts water) to somewhat different.
help avoid transmitting the disease from one
branch to another, although there is some dis- Pear scab
agreement about the effectiveness of disinfection.
Lysol is less corrosive than bleach to the metal Pear scab (Venturia pirina), a fungal disease
parts 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 as
tant carried in an apron rather than a plastic hol- apple scab is on apples. Nevertheless, it can cause
ster 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. Organic
of 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 Organic
Blossom blast and Low-spray Apple Production for details, includ-
ing the use of the Mills Table to predict infection
Another bacterial disease, blossom blast (causal periods.
organism: Pseudomonas syringae, not to be con-
fused with Psedomonas fluorescens discussed Other diseases
above), may afflict pears, usually as a blossom
blight resulting in reduced fruit set. It can also Two foliar diseases, fabraea leaf spot (Fabraea
cause twig dieback and bark cankers, and may maculata) and mycosphaerella leaf spot
lead to severe wood damage of Asian-pear culti- (Mycosphaerella pyri), are usually no problem in
PAGE 4 //ORGANIC PEAR PRODUCTION

5. sprayed orchards but can reach damaging levels control has made organic pear production viable
in unsprayed ones (9). Susceptible cultivars, for the first time in states like Michigan (10). The
which include nearly all European pears, can be psylla also has a number of natural enemies such
defoliated, 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 and
ketable 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 combined
maladies 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 bugs
information on Surround is available in ATTRA’s
Insect IPM in Apples: Kaolin Clay. Stink bugs, tarnished plant bug, and other true
bugs (insects in the order Hemiptera) will readily
Insect and Mite Pests feed on pears throughout the growing season.
Early feeding damage may result in a pucker or
Many 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-called
More information on dealing with these pests can “stone cells” immediately beneath the feeding
be 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 affected
larly affect pears are discussed below. Proper fruit.
pest identification and orchard scouting are key
to implementing successful IPM programs. Some fruit and nut growers reduce true-bug
ATTRA’s Biointensive Integrated Pest Management damage by maintaining unmown leguminous
(IPM) publication provides additional informa- trap crops (clovers, vetches, peas, etc.) near the
tion. 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 the
crop’s most significant insect pest. In conjunc- relatively new biological insecticides derived
tion with fireblight, pear psylla is largely respon- from the seeds of the neem tree are effective
sible 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 Organic
fruit 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 pome
count 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 Gowan
weaken trees in areas of heavy infection. Company (13).
Although the psylla develops resistance to insec- Mites
ticides, it can usually be controlled either with
dormant oil sprays or with sulfur sprays (but not In high enough numbers, pearleaf blister mites
a combination of the two, which damages plants.) (Phytoptus pyri) and pear rust mites (Epitrimerus
Insecticidal soap can reduce active populations pyri) can reduce the photosynthetic efficiency of
during the growing season. Fortunately, the re- leaves and cause russeting on fruit. Both species
cently-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 natural
psylla. In fact, use of Surround for pear psylla predators. These predators—including green
//ORGANIC PEAR PRODUCTION PAGE 5

6. lacewings, predatory mites, and various species
Peshastin Creek Growers Areawide
of ladybird beetles, as well as bigeyed bugs,
Organic Project
minute pirate bugs, and predatory thrips—will
In a Washington valley, twelve family-owned
usually control mite outbreaks if they are not dis-
orchards with approximately 300 acres of
rupted by dust or pesticides. Orchard monitor-
pears have joined together to establish
ing can help establish whether adequate num-
an areawide insect pest management
bers 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 Miller
Neither horticultural oils nor other materials
Co-Chairpersons
approved for organic production provide eco-
P.O. Box 55
nomic control of damaging populations.
Peshastin, WA 98847
(509)548-4207
Another pest that contributes to poor yields and
nichorch@rightathome.com
smaller fruit is the spider mite. Dormant horti-
http://entomology.tfrec.wsu.edu/
cultural oils and insecticidal soaps can both help
pearent/pcg%20home%20page.htm
control 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. commercial
more sensitive to mite feeding than Asian pears,
orchards.
and any pear that is drought-stressed will be
more susceptible to mite damage (14).
Asian pears are slightly less cold-hardy than Eu-
ropean types; they may suffer tissue damage at
Other insects
temperatures below –10° F but are generally
hardy to –20°, making them best adapted to
Other insect pests that may affect pears include
USDA climatic zones 5–9. Most Asian pears
codling 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 to
Organic and Low-spray Apple Production publica-
freezing in areas with a highly variable spring
tion. The pear slug (actually a sawfly larva)
climate.
causes leaf damage; it can be controlled with a
forceful 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 significant
bud moth, variegated leafroller, and redbanded
difference is the common tendency for many of
leafrollers—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 soon
ing disruption tools that are effective for some
after bloom. Shinko, a popular cultivar because
leafrollers 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 quality
Asian Pears will suffer. On the other hand, thinning to pro-
mote fruit size may result in reduced yield per
Because 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 European
are also known as Oriental pears, nashi, sand pears is that Asian pears ripen on the tree—they
pears, apple pears, or salad pears. The more than do not have to be picked and then cured like
1,000 varieties of Asian pear range widely in European pears. This is an advantage for most
PAGE 6 //ORGANIC PEAR PRODUCTION

7. growers, especially growers who are retailing based on these factors, and the premium that
direct to consumers. The fruit can be tree rip- organic growers can expect to receive for their
ened and is ready to eat when picked, or can be product is unpredictable at best.
held in cold storage. You do not have to educate
the 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 winter
many Asian-pear varieties must be carefully pears were consumed by no more than half of
handled 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 Bureau
of Asian pears discolors quickly following rough showed that only 3 out of 10 people have tried
handling, making careful picking and packag- d’Anjou pears, and 2 out of 10 have tried Boscs.
ing a necessity, and mechanical handling risky. One of the obstacles limiting pear consumption
To prevent damage to Asian pears, it may be best is that many consumers do not know how to
to pack them into padded boxes or trays in the ripen them. Providing information on ripening
field where they are picked. may help increase sales (though the Pear Bureau
study also found that most people preferred to
More 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 handled
Economics and Marketing gently, no matter what stage of ripeness they
have reached. Rough handling causes brown
Worldwide, China is by far the world’s largest marks on the skin that may not appear until the
pear-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 to
U.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 a
large scale throughout the United States. How- The market for Asian pears is mixed. Until 1995
ever, because of the prevalence of fireblight in or so, the wholesale market for Asian pears was
the humid eastern and southern states, most pear quite open and prices were high, particularly on
production 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 have
pears produced in the U.S. are grown in Wash- been heavily planted in California for more than
ington, Oregon, and Northern California (16). 20 years, and those orchards are now mature and
Bartletts remain the most popular pear variety bearing, more than meeting local demand and
grown commercially in the U.S., outnumbering causing price drops in some areas.
all other species combined.
On the other hand, outside of California, Asian
Bartlett 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—report
producers who continue to grow them (15). In brisk sales and good prices from locations across
general, 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. 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. UC
opportunity for producers as market awareness IPM Pest Management Guidelines: Pear
and demand continue to grow. Psylla. UC DANR Publication 3339.
Accessed August 2002. <http://
References www.ipm.ucdavis.edu/PMG/
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. IPM
2) Hall-Beyer, Bart, and Jean Richard. 1983. Report. Spring. p. 1. Accessed August
Ecological Fruit Production in the North. 2002 at <http://www.msue.msu.edu/
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 5569
4) Ames, Guy. 2000. Personal communica- Yuma, AZ 85366-5569
tion. 1-800-883-1844 ext. 2
http://www.aza-direct.com/
5) 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
www.ams.usda.gov/nop/NationalList/ 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. Agricultural
7) 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. <http://www.fas.usda.gov/htp2/
8) 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
<http://www.ipm.ucdavis.edu/PMG/ Milwaukie, OR 97222-4635
r603100111.html>. 503-652-9720
http://www.usapears.com/
9) 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. The occurrence of disease—any disease on any
plant 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 fact
is very important to understanding fireblight in-
cidence in pear orchards, especially in terms of
managing this potentially devastating disease in
different parts of the country.

10. resistant,” he or she is speaking in relative terms. which is especially prone to infection and seems
Usually we read or hear something like “some- to provide the disease its fastest entry into the
what resistant,” “very resistant,” “moderately re- wood.
sistant,” “slightly susceptible,” etc. To further
complicate matters, different researchers use dif- Another practice that can be adjusted to alter the
ferent rating scales to describe resistance/suscep- orchard environment is pruning, which can
tibility—there is no agreed-upon standard. For “open up” a tree to allow more rapid drying of
example, 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 to
mate of damage, while others may use more ab- reduce pruning in order to avoid fostering the lush
solute measurements, such as the centimeters of shoot growth (which is more susceptible to
shoot 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 high
greatly 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 as
trude into any wood older than one year. In con- “fireblight resistant”—is relatively resistant in
trast, when all three factors of the disease triangle the climate of California, but can suffer severe
conspire, 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 trees
of our efforts as growers. When we spray cop- disappear one-by-one and year-by-year.
per, Blight Ban™, or one of the antibiotics, we
are trying to reduce or exclude (in the case of
Blight Ban) the pathogen from potential infec- By Martin Guerena and Holly Born
tion sites. There is also a geographic component NCAT Agriculture Specialists
to this part of the triangle, as E. amylovora is much Updated by Tracy Mumma
less prevalent in some parts of the world than in
others. Edited by Richard Earles
Formatted by Cynthia Arnold
The third face of the triangle—an environment
conducive to the disease—is also related to ge- April 2003
ography, mostly by climate. Where the climate
is warm and wet, expecially in the spring,
fireblight infection and development are favored.
The more arid parts of the western U.S. are not
nearly as prone to fireblight problems as most of The electronic version of Organic Pear Production
the East. But these large climatic and geographic is located at:
HTML
features are not the only components of a dis-
http://www.attra.ncat.org/attra-pub/pear.html
ease-promoting or disease-suppressive environ-
PDF
ment—the orchardist can manipulate parts of the http://www.attra.ncat.org/attra-pub/PDF/pear.pdf
orchard micro-environment to help suppress dis-
ease development. For example, reducing fer- IP167
tilization can limit fast-growing succulent tissue,
PAGE 10 //ORGANIC PEAR PRODUCTION