WalnutsWalnuts

By Melissa ClarkBy Melissa Clark

The Origin of WalnutsThe Origin of Walnuts

Walnuts are native to Asia, Europe, and Walnuts are native to Asia, Europe, and North America--having predated the North America--having predated the separation of continents 60 million years separation of continents 60 million years ago.ago.

Persian walnuts are supposed to have Persian walnuts are supposed to have originated in southeast Europe and originated in southeast Europe and warm parts of Asia.warm parts of Asia.

In 16In 16thth Century England they were called Century England they were called WAL WAL nuts, from “WAL” meaning nuts, from “WAL” meaning “foreign.”“foreign.”

Importation to SJVImportation to SJV

Walnuts came to the new world with Walnuts came to the new world with English settlers, and to California via English settlers, and to California via missionaries.missionaries.

Today, walnut production is almost entirely Today, walnut production is almost entirely located in the San Joaquin/Sacramento located in the San Joaquin/Sacramento valleys of California.valleys of California.

Over 5,000 growers and 52 processors Over 5,000 growers and 52 processors make up a highly organized and productive make up a highly organized and productive industry. industry.

There are 17 recognized species--all edible.There are 17 recognized species--all edible.

PollinationPollination

Most walnuts are self-fertile, but Most walnuts are self-fertile, but sometimes require another cultivar sometimes require another cultivar for pollination.for pollination.

Too much cross pollination results in Too much cross pollination results in a condition known as flower a condition known as flower abscission.abscission.

Walnuts are wind pollinated and Walnuts are wind pollinated and pollen will carry about 250-300ft in pollen will carry about 250-300ft in mature orchards.mature orchards.

SoilsSoils

The best soils are deep, well-drained silt The best soils are deep, well-drained silt loams with pH 6 to 8, as found in central loams with pH 6 to 8, as found in central valleys of California.valleys of California.

Walnuts and related species are generally Walnuts and related species are generally deep-rooted (9-12 ft), and strongly tap-rooted, deep-rooted (9-12 ft), and strongly tap-rooted, if no restrictive layers are present in soils. if no restrictive layers are present in soils.

Irrigation is necessary in the arid climates Irrigation is necessary in the arid climates walnuts are grown. Up to 4 acre-feet of water walnuts are grown. Up to 4 acre-feet of water are applied per year in California.are applied per year in California.

ClimateClimate

In California, trees are considered cold hardy In California, trees are considered cold hardy to 12-15°F.to 12-15°F.

Rainfall in spring at bud break, or in mid-Rainfall in spring at bud break, or in mid-summer greatly increases the severity of summer greatly increases the severity of walnut blight.walnut blight.

High temperatures and/or high sunlight can High temperatures and/or high sunlight can cause sunburn, darkening, and shriveling of cause sunburn, darkening, and shriveling of kernels.kernels.

Temperatures too cool in summer can result in Temperatures too cool in summer can result in inadequate kernel development or "nut fill".inadequate kernel development or "nut fill".

FruitFruit

Nuts are borne singly or in clusters of 2-3 on Nuts are borne singly or in clusters of 2-3 on shoot tips. A green, fleshy shuck surrounds the shoot tips. A green, fleshy shuck surrounds the nut, which splits irregularly at maturity. nut, which splits irregularly at maturity.

The shell is rough, wrinkled or furrowed, and The shell is rough, wrinkled or furrowed, and thin.thin.

Nut size ranges from 32-45 nuts/lb in Persian Nut size ranges from 32-45 nuts/lb in Persian walnut, and 22-35 nuts/lb in black walnut.walnut, and 22-35 nuts/lb in black walnut.

Walnuts mature from 4.5-5 months after Walnuts mature from 4.5-5 months after flowering, and are harvested in September-flowering, and are harvested in September-October.October.

Pest ControlPest Control Aphid feeding can reduce tree vigor and Aphid feeding can reduce tree vigor and

nut size, yield, and quality. nut size, yield, and quality. In most orchards, walnut aphids are kept In most orchards, walnut aphids are kept

below damaging levels by an introduced below damaging levels by an introduced parasitic wasp.parasitic wasp.

First generation codling moth larvae First generation codling moth larvae reduce yield directly by causing nutlets reduce yield directly by causing nutlets to drop from the tree.to drop from the tree.

Management include pheromone mating Management include pheromone mating disruption, insecticide sprays, and disruption, insecticide sprays, and biological control.biological control.

Crown Gall ControlCrown Gall Control

Crown gall appears as rough, Crown gall appears as rough, abnormal galls at or below the soil abnormal galls at or below the soil surface on roots or trunk.surface on roots or trunk.

Young trees become stunted and Young trees become stunted and older trees often develop secondary older trees often develop secondary wood rots.wood rots.

The incidence of crown gall can be The incidence of crown gall can be reduced by planting non-infected, reduced by planting non-infected, "clean" trees. "clean" trees.

Walnut Blight ControlWalnut Blight Control

In walnut blight, one to several black In walnut blight, one to several black lesions may appear on catkins.lesions may appear on catkins.

Infected nuts develop black, slightly Infected nuts develop black, slightly sunken lesions at the flower end and sunken lesions at the flower end and on the sides of the nut as it matures.on the sides of the nut as it matures.

In orchards with histories of walnut In orchards with histories of walnut blight damage, protective blight damage, protective treatments during prolonged wet treatments during prolonged wet springs are necessary for adequate springs are necessary for adequate protection. protection.

ProductionProduction United StatesUnited States (2002 USDA) - 282,000 (2002 USDA) - 282,000

MT or 564 million lbs of in-shell nuts. MT or 564 million lbs of in-shell nuts. Walnuts are produced commercially in 48 Walnuts are produced commercially in 48

countries on 1,527,000 acres.countries on 1,527,000 acres. There are about 200,000 acres of walnuts There are about 200,000 acres of walnuts

in California's central valley.in California's central valley. Exports are equivalent to 18% of total Exports are equivalent to 18% of total

production. Principal destination production. Principal destination countries are Japan, Germany, Spain, Italy countries are Japan, Germany, Spain, Italy and Israel.and Israel.

Economic ValueEconomic Value The industry value is $305 million, The industry value is $305 million,

fluctuating between $275-380 million fluctuating between $275-380 million over the last decade.over the last decade.

In Tulare County in 2004, walnut crops In Tulare County in 2004, walnut crops were valued at $70,609,000.were valued at $70,609,000.

Yield averages 2820 lbs/acre, but some Yield averages 2820 lbs/acre, but some orchards can produce up to 6000 orchards can produce up to 6000 lbs/acre.lbs/acre.

Prices paid to growers are 54 ¢/lb, on the Prices paid to growers are 54 ¢/lb, on the low end of the 50 to 79 ¢/lb range over low end of the 50 to 79 ¢/lb range over the last decade. the last decade.

Cost of Local ProductsCost of Local Products

Whole walnuts sold in bulk: $1.27/lbWhole walnuts sold in bulk: $1.27/lb Whole walnuts sold in a 1lb. Whole walnuts sold in a 1lb.

package: $1.88package: $1.88 Shelled walnuts sold in a 1lb. Shelled walnuts sold in a 1lb.

package: $3.87package: $3.87

(source: Food Max, Visalia Ca.)(source: Food Max, Visalia Ca.)

Cultural UsesCultural Uses

The wood is heavy and fine-grained, The wood is heavy and fine-grained, used mostly for furniture and gun used mostly for furniture and gun stocks. stocks.

The husk yields a valuable oil and a The husk yields a valuable oil and a yellow dye when pressed; the oil is yellow dye when pressed; the oil is used in soaps, paints, and dyes.used in soaps, paints, and dyes.

Shells are ground and used as anti-Shells are ground and used as anti-skid agents for tires.skid agents for tires.

Medicinal UsesMedicinal Uses

Black walnut tincture, an extract made with Black walnut tincture, an extract made with grain alcohol, is an antiseptic that is high in grain alcohol, is an antiseptic that is high in iodine used for treating fungus conditions.iodine used for treating fungus conditions.

It is derived from fresh green hulls of the It is derived from fresh green hulls of the black walnut tree and is said to kill adult black walnut tree and is said to kill adult and developmental stages of at least 100 and developmental stages of at least 100 parasites.parasites.

  Ellagic acid is found in leaves and fruits; it Ellagic acid is found in leaves and fruits; it is being studied for use as a cancer therapy is being studied for use as a cancer therapy drug.drug.

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