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Walnuts: Calendar of Operations

for Home Gardeners


Pamela M. Geisel is UC Cooperative Extension Farm Advisor in Environmental Horticulture for

Fresno County; Carolyn L. Unruh is UCCE staff writer for Fresno County; and Paul Vossen is


UCCE Farm Advisor in Fruits, Vegetables, and Marketing for Sonoma and Marin Counties.


University of California

Agriculture and Natural Resources

Publication 7263


Walnuts make lovely shade trees, in addition to pro-

ducing a delightful nut. Various types of walnuts are

grown in California, but the most popular are the

English varieties. They have a moderate chilling

requirement of about 500 to 1,000 hours. Shoots and

flowers of the early varieties can be damaged by late

spring frosts in cold areas. They do best in deep, well-

drained, medium-textured soils. Walnut trees require

regular irrigation for a quality nut crop, but once

established they can tolerate periods of drought. They

generally do poorly when planted in lawns: frequent

irrigations promote root diseases to which walnut

trees are susceptible.


Winter Dormant Season

1.Prune mature trees by thinning out limbs in


crowded parts of the canopy to let light into the

whole tree. Remove broken and dead branches.


2.Remove and destroy old nuts on trees and on

the ground to kill resident larvae of codling

moths and navel orangeworms and to help

reduce damage from these insects the following

year.


Spring Bloom Season

1.Spray for blossom blight when female flowers


appear (they appear as tiny green nuts with

feathery pistils) and at 10- to 14-day intervals

until rainy weather stops. Use bordeaux or

another fixed-copper material and provide thor-

ough coverage of the whole tree. Blossom blight

appears in June as black discoloration at the

blossom end of nuts, and later as black, hollow

nuts.


2.If scale is a problem, monitor the scale popula-

tion and treat with narrow-range oil when the

crawlers appear. Do not apply oil when temper-

atures go above 90°F, and do not use it in trees

that have been stressed by drought, heavy scale

populations, or other factors. Irrigate the trees

well prior to oil application.


3.Remove all weeds from around the base of the

trees, and keep this area dry in summer to

reduce root and crown rot problems.


4.Fertilize mature trees with about 8 to 10 pounds

of ammonium sulfate (depending upon tree size)

just before or during a rain or the first irrigation.


5.In very hot regions, paint the trunks and lower

branches of newly planted young trees with a 1:1

mixture of white interior latex paint and water to

prevent sunburn injury and to reduce borer

infestations.


Summer Growing Season

1.To reduce the incidence of codling moth and


navel orangeworm in the current growing sea-

son, gather and destroy any damaged immature

nuts that fall to the ground or remain on the tree.

Clean-up is especially important in May and

June.


2.If you use drip irrigation, apply just the amount

of water needed to replace what is used by the

tree and lost from the soil through evaporation. If

you use sprinkler or flood irrigation, water about

every three to four weeks during the summer

months. Young, small trees will need about 4 to

12 gallons of water per day, and large trees about

30 to 50 gallons per day. In garden settings some

of this demand is usually met by water applied

to nearby plants. Water requirements will vary

depending on your soil type and environmental

conditions. Irrigate at the drip line, well away

from the trunk of the tree.


3.Walnut husk fly larvae may cause considerable

damage to the green outer hull of walnuts, but

rarely do they affect the kernels inside the shells.

If walnut husk fly attacks have a history as a

recurring problem, spray with malathion at 21-

day intervals beginning about August 1. The

effectiveness of walnut husk fly sprays is signifi-

cantly increased if you add molasses to the spray

at 1 to 1.5 times the amount of malathion. For

example, if the label recommends 2 teaspoons

per gallon of malathion, add 3 teaspoons of

molasses as well. Always follow the label-recom-

mended rates for malathion and other chemicals.

When using a malathion-molasses mix, it is gen-

erally sufficient to spray just the lower 1/3 to 1/2

of the tree.


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California, Agriculture and Natural Resources, 300 Lakeside Drive, 6thFloor, Oakland, CA 94612-3550; 510-987-0096. For informa-

tion on how to obtain this publication and other ANR CS products, call 800-994-8849.


pr-1/02-JWC/CY


This publication has been anonymously peer reviewed for technical accuracy by University of

California scientists and other qualified professionals. This review process was managed by the

ANR Associate Editor for Pomology, Viticulture, and Subtropical Horticulture.


Autumn

1.To keep worm damage to a minimum, harvest


nuts as early as possible. Shake or pole the trees

when the green hulls begin to crack and separate

from the shells. Remove the hulls as soon as pos-

sible after harvesting and discard them. Wear

gloves to avoid staining your hands.


2.Place the hulled walnuts in a warm, well-venti-

lated area to dry. Store in-shell nuts in a cool, dry

place in sealed plastic bags after they have been

frozen for a few days to kill any insect eggs that

may have been present. You can shell walnuts

when the kernels have dried enough so that they

break easily when bent. Shelled nuts may be

stored for several months to a year in the refrig-

erator or freezer. In general, storage life for

shelled nuts is shorter at room temperature than

in a refrigerator or freezer.


For More Information


Cousult these UC IPM Pest Notes online at
http://www.ipm.ucdavis.edu:


Aphids

Bordeaux Mixture

Codling Moth

Scales

Spider Mites

Walnut Husk Fly


You’ll also find detailed information on many aspects of

fruit and nut tree care in these titles and in other publi-

cations, slides sets, and videos from UC ANR:


California Master Gardener Handbook, publication 3382

Drip Irrigation in the Home Landscape, publication 21579

Pests of the Garden and Small Farm, publication 3332

Pruning Fruit and Nut Trees, publication 21171

Sweet Cherries for the Home Grounds, publication 2951

The UC Guide to Solving Garden and Landscape Prob-

lems, CD-ROM 3400

ORDERING


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orders by mail, phone, or fax, or request a printed cata-

log of publications, slide sets, and videos from


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Agriculture and Natural Resources

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Visit the ANR Communication Services website at
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Publication 7263


© 2002 by the Regents of the University of

California, Division of Agriculture and Natural

Resources. All rights reserved.


2 • Walnuts: Calendar of Operations for Home Gardeners


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http://anrcatalog.ucdavis.edu/
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WARNING ON THE USE OF CHEMICALS

Carefully follow all precautions and safety recommendations given on the container label. Store all chemicals in

their original labeled containers in a locked cabinet or shed, away from foods or feeds, and out of the reach of chil-

dren, unauthorized persons, pets, and livestock.

Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens con-

taining fruits and/or vegetables ready to be picked.

Mix and apply only the amount of pesticide you will need to complete the application. spray all the material

according to label directions. Do not dispose of unused material by pouring down the drain or toilet. Do not pour

on ground: soil or underground water supplies may be contaminated. follow label directions for disposing of con-

tainer. Never burn pesticide containers.

PHYTOTOXICITY: Certain chemicals may cause plant injury if used at the wrong stage of plant development or

when temperatures are too high. Injury may also result from excessive amounts or the wrong formulation or from

mixing incompatible materials. Inert ingredients, such as wetters, spreaders, emulsifiers, diluents, and solvents,

can cause plant injury. Since formulations are often changed by manufacturers, it is possible that plant injury may

occur, even though no injury was noted in previous seasons.


Funding for this publication was made possible through a grant from the Elvenia J. Slosson Fund.


Walnuts: Calendar of Operations for Home Gardeners • 3


Introduction

Winter Dormant Season

Spring Bloom Season

Summer Growing Season

Autumn

For More Information

WARNING ON THE USE OF CHEMICALS


Text7: ISBN 978-1-60107-054-8

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