Table of Contents
Reid, W. 1990. Eastern black walnut: Potential for commercial nut producing
cultivars. p. 327-331. In: J. Janick and J.E. Simon (eds.), Advances in new
crops. Timber Press, Portland, OR.
Eastern Black Walnut: Potential for Commercial Nut Producing Cultivars
- GENETIC TRAITS IMPORTANT FOR IMPROVED NUT PRODUCTION
- Lateral Bud Fruitfulness
- Late Leafing
- Anthracnose Resistance
- Precocity and Productivity
- Nut Quality
- CURRENTLY AVAILABLE CULTIVARS
- FUTURE PROSPECTS FOR CROP DEVELOPMENT
- Table 1
- Fig. 1
The Eastern black walnut, Juglans nigra L., is valued for both the fine
cabinet wood it produces and the high quality edible nuts it bears. Juglans
nigra is found growing throughout the Eastern U.S. (Fig. 1). The range of
this species extends from Kansas eastward to the Atlantic seaboard, from
Minnesota to Texas in the West, and from New England to Northern Florida in the
East (Fowells 1965). Within their native distribution, black walnuts grow in a
wide range in climatic conditions (Funk 1979). Black walnuts are found growing
in USDA plant hardiness zones 4 through 8 and are adapted to growing seasons
that range from 140 to 280 days. Rainfall within the native range varies from
178 cm/year in the Appalachian mountains to 64 cm/year in northern Nebraska.
Trees can be found growing in many different sites but they grow best in deep,
well-drained alluvial soils.
The fruit produced by the black walnut is a drupe-like nut surrounded by a
fleshy, indehiscent exocarp. The nut has a rough, furrowed, hard shell that
protects the edible seed. Fruits are usually produced in clusters of 2 to 3
and are borne on the terminals of the current season's growth. The seed is
sweet, oily and high in protein.
Over 10,000 metric tons of black walnuts are harvested annually in the United
States. This production is based entirely on hand harvested nuts from seedling
trees growing in native stands throughout the Midwest and Northeast. Harvested
nuts are brought to local buying stations where they are hulled and bagged for
shipment to a commercial sheller. Until recently only one commercial sheller,
Hammons Products Co., Stockton, Missouri, bought and processed black walnuts.
In 1988 a second firm, Indiana Walnut Products Co., West Lafayette, began
buying and shelling nuts. Sixty percent of commercially processed black walnut
kernels are packaged for the retail trade, 30% are used in the manufacture of
ice cream while the remaining 10% are used in commercial baking and candy
making (Hammons 1973). Well-managed, seedling black walnuts produce nuts
averaging 20% kernel (Zarger 1946) but in commercial shelling operations only 6
to 10% usable nut meat is recovered. In contrast, over 40% nut meat is
recovered in the commercial shelling of Persian walnuts. The low kernel yields
for black walnut has forced shellers to develop products manufactured from
their main waste product, walnut shells. Ground black walnut shells are used
for metal cleaning and polishing, oil well drilling, and as an ingredient in
paint, explosives, and make-up (Cavende 1973). Utilization of the shell has
been the primary reason a black walnut industry based on seedling nuts has
'Thomas', the first black walnut selected for nut production, has been
propagated since 1881 (Heiges 1896). Since that time over 750 cultivars have
been selected and named. For the most part these cultivars were selected by
amateur nut growers from the native population solely on the basis of nut
quality characteristics. Although black walnut is not a new crop, the growing
of walnut trees solely for nut production remains the passion of backyard
enthusiasts. The commercial production of black walnuts from orchards of
superior nut producing cultivars is nonexistent.
Black walnut is an under-exploited crop. All genetic improvement programs for
black walnut have concentrated on increasing its value for limber (Beineke
1983) and not for nut production. The potential for generic improvement in nut
yield, percent kernel and kernel quality is great. Even under the low level of
selection pressure applied by amateur nut growers, cultivars have been
identified that exhibit one or more of the important generic traits needed for
further crop improvement.
Black walnut has great genetic potential for improved nut yield and quality The
extensive naive range of this species has ensured a large gene pool from which
advanced selections can be made. Generic traits that would lead to advances in
a tree improvement program include: lateral bud fruitfulness, late leafing,
resistance to the anthracnose fungi, Gnomonia leptostyla, (Fr.) Ces.
& Not., precocity and productivity and improved nut quality.
The selection of clones that produce pistillate flowers on lateral buds has
resulted in significant yield increases in Persian walnut, J. regia
(Ramos et al. 1984). Lateral bearing Persian walnut cultivars tend to be more
precocious and are better suited to high yielding, high density plantings. The
lateral bearing characteristic is also found in black walnut (Sparks 1982).
Black walnut trees exhibiting this characteristic have a profusion of short,
spur type branches distributed along main scaffold limbs. With this growth
pattern, both leaves and nuts are borne throughout the tree canopy resulting in
increased yield potential. The heritability of the lateral bearing
characteristic is unknown for black walnut but Hansche et al. (1972) found this
trait to have a moderate level of heritability in Persian walnut.
Black walnut is quite susceptible to freezing temperatures once growth begins
in the spring. Entire shoots are killed by temperatures below -2°C.
Pistillate flowers are borne on the terminals of these frost tender shoots and
a late spring frost can destroy all potential for nut production. Late leafing
clones can avoid yield losses due to frost. Date of leafing in black walnut
has a high degree of heritability (Kucera et al. 1974) but leafing dates for
currently propagated cultivars are unknown. In addition to frost avoidance,
late leafing black walnut clones may avoid infections by the walnut blight
bacterium, Xanthomonas campestris pv juglandis in the same manner
as late leafing Persian walnut cultivars (Forde 1975). Further, immature or
expanding black walnut leaves have shown the greatest resistance to infection
by the anthracnose fungi (Cline and Neely 1984), thus the late leafing
characteristic may also contribute to anthracnose infection avoidance.
The anthracnose fungus attacks leaves, new shoots and fruit of the black
walnut. Initial foliar infections begin shortly after full leaf expansion
during extended periods of leaf wetness (Kessler 1984). The disease progresses
rapidly in mid-summer and results in premature defoliation by late August This
premature leaf drop is one of the major causes of poor kernel fill (Reid 1986)
and alternate bearing (Sparks 1979) in black walnut. Complete resistance to
the anthracnose fungi has not been found although a wide range in
susceptibilities exists (Beineke and Masters 1973, Berry 1960). The 'Thomas'
and 'Ohio' black walnut cultivars have been noted for their anthracnose
resistance, although both cultivars will contract the disease under conditions
of high disease pressure (Berry 1960). Heritability for anthracnose resistance
is high (Beineke and Masters 1973) indicating genetic gains in resistance to
this devastating disease can be made.
High development costs for establishing a walnut orchard demand the planting of
cultivars that bear large crops at an early age. Cultivars displaying lateral
bud fruitfulness generally come into production well in advance of non-lateral
bearing cultivars. The precocity and productivity of black walnut cultivars
have not been studied but should be prime considerations in selecting new
cultivars. If lateral bearing black walnuts are similar to lateral bearing
Persian walnuts, first commercial yields should be expected in the fifth year
after establishment. Mature orchards should be able to produce more than 2
t/ha of hulled walnuts.
Nut quality characteristics have been the primary focus of the evaluation of
black walnut cultivars. Over 400 cultivars have been named and their nuts
evaluated for nut weight and percent kernel (Berhow 1962; Zarger 1945). Nut
samples are evaluated annually by many State nut growers associations. Results
from 28 years of nut evaluations in Kansas are summarized for selected
cultivars in Table 1.
Shell thickness and structure are the most important determinant of percent
kernel and nut crackability. The highest quality walnuts have a thin outer
shell with no internal convolutions protruding into the nut meat. The inner
shell partition between kernel halves should be very thin to allow easy removal
of kernel pieces. Most thin shelled black walnut cultivars yield over 30%
kernel. The heritability of a thin shell has not been studied for black walnut
but in Persian walnut, heritability for shell thickness is high (Hansche et al.
Kernel quality and plumpness is strongly influenced by tree care and harvesting
practices (Chase 1941), but with trees receiving optimum care, wide differences
in kernel quality still exist between cultivars. High quality walnuts have
light colored kernels with an absence of kernel veins. Dark colored or
strongly veined kernels are associated with rancidity by consumers. Kernel
color and venation are under a moderate level of genetic control in Persian
walnut (Hansche et al. 1972) and a similar level of heritability should be
expected for black walnut.
Several currently available cultivars deserve further evaluation for their
potential as commercial orchard trees. Cultivars that bear nuts on laterals
branches and produce nuts with more than 30% kernel are the primary candidates
for commercial plantings. These cultivars include, 'Cranz', 'Football 11', and
'Sparks 127' (Table 1). 'Clermont', 'Kwik-Krop', and 'Sparrow' have been noted
for their consistent productivity and should be evaluated further. Black
walnut cultivars are not widely available from commercial nurseries and initial
trials will most probably be developed by field grafting seedling rootstocks.
Large areas of crop land in the Midwest are suited to the production of black
walnut (Noweg and Kurtz 1985). Lands no longer suitable for profitable corn or
soybean production often provide adequate sites for black walnut orchards. The
technology for the cultivation and mechanical harvesting of this crop currently
exists because techniques and equipment can be easily adapted from the Persian
walnut industry A well developed market and marketing system based on seedling
black walnuts is already in place and could rapidly change to accommodate thin
shelled, high quality cultivars.
Commercial black walnut orchards based on thin shelled cultivars have not been
developed due to the lack of cultivar performance data and undemonstrated crop
profitability. Large trial plantings of currently available cultivars that
become financially successful will be necessary to stimulate a black walnut
orchard industry. The incorporation of additional positive traits into walnut
cultivars will only be made after an established black walnut industry demands
further crop improvement.
- Beineke, W.F. 1983. Genetic improvement of black walnut for timber production.
Plant Breed Rev. 1:236-266.
- Beineke, W.F. and C.J. Masters. 1973. Black walnut progeny and clonal tests at
Purdue University Proc. 12th South. Forest Tree Improvement Conf., Baton Rouge,
LA. p. 233-242.
- Berhow, S. 1962. Black walnut varieties-a reference list. Northern Nut Growers
Assoc. Annu. Rpt. 53:63-69.
- Berry F.H. 1960. Etiology and control of walnut anthracnose. Maryland Agric.
Expt. Sta. Res. Bul. A-113.
- Cavender, C.C. 1973. Utilization and marketing of shells. p. 77-78. In: Black
walnut as a crop. USDA Forest Serv. Gen. Tech. Rpt. NC-4.
- Chase, S.B. 1941. Effect of handling methods on the color and flavor of black
walnut kernels. Northern Nut Growers Assoc. Annual Report. 32:34-37.
- Cline, S. and D. Neely. 1984. elationship between juvenile-leaf resistance to
anthracnose and the presence of juglone and hydrojuglone glucoside in black
walnut. Phytopathology 74:185-188.
- Forde, H.I. 1975. Walnuts, p. 439-455. In: J. Janick and J. Moore (eds.).
Advances in fruit breeding. Purdue Univ. Press, West Lafayette, IN.
- Fowells, H.A. 1965. Silvics of forest trees of the United States. USDA
Agriculture Handb. 71. p. 203.
- Funk, D.T. 1979. Black walnuts for nuts and timber. p. 51-73. In: R.A. Jaynes
(ed.), Nut tree culture in North America. Northern Nut Growers Association,
- Hammons, R.D. 1973. Utilization and marketing of nuts. p. 75-76. In: Black
walnut as a crop. USDA Forest Serv. Gen. Tech. Rpt. NC-4.
- Hansche, P.E., V. Beres, and H.I. Forde. 1972. Estimates of quantitative
generic properties of walnut and their implications for cultivar improvement.
J. Amer. Soc. Hort. Sci. 97:279-285.
- Heiges, S.B. 1896. Nut culture in the United States. USDA Gov. Printing Office,
- Kessler, K.J. 1984. Similarity of annual anthracnose epidemics in young
Juglans nigra plantations from 1978 through 1982. Plant Dis.
- Kucera, J.M., C.F. Bey, and F.H. Kung. 1974. Genetic gain for five traits in
black walnut. Proc. 9th Central States Forest Tree Improvement Conf., Ames, IA.
- Noweg, T.A. and W.B. Kurtz. 1985. Eastern black walnut on retired croplands in
the corn belt region: an economic analysis. Northern Nut Growers Assoc. Annu.
- Ramos, D., G. McGranahan, and L. Hendricks. 1984. Walnuts. Fruit Var. J.
- Reid, W. 1986. Reasons for poor kernel filling. Northern Nut Growers Assoc.
Annu. Rpt. 77:37-38.
- Sparks, A. 1982. Lateral bearing black walnuts. Northern Nut Growers Assoc.
Annu. Rpt. 73:33-34.
- Sparks, D. 1979. Physiology-site, growth, flowering, fruiting, and nutrition.
p. 211-239. In: R.A. Jaynes (ed.), Nut tree culture in North America. Northern
Nut Growers Assoc., Hamden, CT.
- Zarger, T.G. 1945. Nut-testing, propagation, and planting experience on 90
black walnut selections. Northern Nut Growers Assoc. Annu. Rpt. 36:23-30.
- Zarger, T.G. 1946. Yield and nut quality of the common black walnut in the
Tennessee valley. Northern Nut Growers Assoc. Annu. Rpt. 37:118-124.
Table 1. A sample of black walnut cultivars exhibiting genetic traits
important for future crop improvement and their nut quality characteristics.
zAll cultivars listed were discovered as chance seedlings of unknown or
|Cultivar ||State of originz ||Percent |
|No. nuts/kgy ||Notable genetic traits|
|'Bowser' ||Ohio ||30.7 ||65.6 ||High kernel quality|
|'Clermont' ||Ohio ||35.5 ||59.0 ||Productive|
|'Cranz' ||Pennsylvania ||31.4 ||71.9 ||Lateral bearing|
|'Emma K' ||Illinois ||35.3 ||62.0 ||Thin shell|
|'Football 11' ||Missouri ||30.0 ||43.1 ||Lateral bearing|
|'Kwik-Krop' ||Kansas ||31.5 ||58.1 ||Precocious, productive|
|'Ohio' ||Ohio ||26.7 ||64.7 ||Anthracnose resistance|
|'Sauber' ||Ohio ||34.1 ||65.6 ||Thin shell, high kernel quality|
|'Sparks 127' ||Iowa ||31.5 ||64.0 ||Lateral bearing|
|'Sparrow' ||Illinois ||28.7 ||58.3 ||Productive|
|'Thomas' ||Pennsylvania ||24.0 ||51.9 ||Anthracnose resistance|
yMeans of data collected in the years 1959-1987 by the Kansas Nut Growers
||Fig. 1. The natural range of Juglans nigra L. in North America
(Source: Fowells 1965).
Last update August 28, 1997