Pecan Diseases and Pests and Their Control

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Title: Pecan Diseases and Pests and Their Control
Author: Rosburg, David W., King, D. R.
Language: English
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MP-313
NOVEMBER 1958

PECAN DISEASES AND INSECTS
AND THEIR CONTROL

TEXAS AGRICULTURAL EXPERIMENT STATION ...
TEXAS AGRICULTURAL EXTENSION SERVICE
College Station, Texas

Key to Pecan Diseases

DISEASES OF THE LEAVES
Olive spots on underside page 5 Scab
Downy, buff, or greenish-yellow lesions page 7 Downy Spot
Small, reddish-brown to gray spots on page 6 Brown Leaf Spot
underside
Dark brown to black lesions on veins page 6 Vein Spot
and stems
Tiny white tufts of fungal growth on page 9 Articularia Leaf Mold
underside
Small olive green velvety spots. By page 7 Leaf Blotch
midsummer, black pimple-like dots
appear in the spots
Leaflets yellowish, mottled, narrowed page 8 Rosette
and crinkled with reddish-brown spots,
may be perforated
Broomy type of twig growth, bunching of page 8 Bunch Disease
leaves
DISEASES OF THE NUTS
Small black sunken or raised spots page 5 Scab
which may fuse to cover entire surface
of shuck
Pink spore masses on shuck surface page 9 Pink Mold
DISEASES OF THE ROOTS
Galls of various sizes on larger roots page 7 Crown Gall
Splitting and deterioration of bark of page 10 Cotton Root Rot
infected roots, strands of buff-colored
fungal growth may be present
NONPARASITIC PLANTS ON THE LIMBS AND BARK
Whitish-gray mosslike masses on the bark page 9 Lichens
Accumulations of grayish strands page 9 Spanish Moss, Ball Moss
hanging from limbs and twigs or
ball-like growth on limbs and branches

Key to Pecan Insects

INSECTS ATTACKING THE NUTS
Olive-green caterpillars up to ½ inch page 10 Pecan Nut Casebearer
long feeding in the nuts, or later in
the season, in the shucks
White caterpillars up to ⅜ inch long page 11 Hickory Shuckworm
tunneling in the shucks
White legless grubs feeding in the nuts page 12 Pecan Weevil
in late summer
Green or brown bugs sucking the sap page 12 Stink Bugs and Plant
from the nuts Bugs
INSECTS ATTACKING THE FOLIAGE
Soft-bodied yellow insects producing page 13 Aphids
honeydew or small black insects causing
yellow blotches on the foliage
Tiny green arthropods in webs near the page 13 Mites
midrib, leaves appear scorched
Caterpillars feeding in gray cases page 14 Pecan Leaf Casebearer
about ½ inch long in the spring; small
winding blotches produced in the leaves
in the summer
Olive-green caterpillars tunneling in page 10 Pecan Nut Casebearer
the shoots in the early spring
Tiny caterpillars in light brown page 15 Pecan Cigar Casebearer
cigar-shaped cases about ¼ inch long
Galls on the leaves, twigs and nuts page 14 Pecan Phylloxera
Leaves eaten in the early spring by a page 14 Sawfly
light green caterpillar which leaves
the midribs and veins intact
Beetles feeding on the foliage at night page 15 May Beetles
Caterpillars in large white webs page 15 Fall Webworm
encasing entire branches
Caterpillars with long soft hairs page 16 Walnut Caterpillar
feeding in colonies on the foliage
without producing webs
Dark gray, active caterpillars up to 3 page 16 Pecan Catocala
inches long feeding on the foliage in
early spring
Masses of frothy white foam enclosing page 16 Pecan Spittlebug
tiny, light green insects in the spring
Tiny greenish caterpillars feeding in page 16 Pecan Bud Moth
the terminals and axils of the buds on
young pecan trees
INSECTS ATTACKING THE LIMBS, TRUNK AND TWIGS
Beetle girdling twigs and limbs in late page 17 Pecan Twig Girdler
summer and fall
Holes about ⅛ inch in diameter in dying page 17 Red-shouldered
limbs Shot-hole Borer
White borers with an enlargement behind page 17 Flatheaded Borers
the head tunneling underneath the bark
of trunk and limbs
Limbs encrusted with scales, which page 18 Obscure Scale
closely resemble the color of the bark

CONTENTS

Key to Pecan Diseases 2
Key to Pecan Insects 2
Spray Schedule for the Control of Pecan Diseases and Insects 4
Introduction 5
Pecan Diseases and Their Control 5
Scab 5
Brown Leaf Spot 6
Vein Spot 6
Leaf Blotch 7
Crown Gall 7
Downy Spot 7
Bunch Disease 8
Rosette 8
Lichens 9
Articularia Leaf Mold 9
Pink Mold 9
Spanish and Ball Moss 9
Cotton Root Rot 10
Pecan Insects and Their Control 10
Pecan Nut Casebearer 10
Hickory Shuckworm 11
Pecan Weevil 12
Stink and Plant Bugs 12
Aphids 13
Mites 13
Pecan Leaf Casebearer 14
Pecan Phylloxera 14
Sawflies 14
May Beetles 15
Pecan Cigar Casebearer 15
Fall Webworm 15
Walnut Caterpillar 16
Pecan Catocala 16
Pecan Spittlebug 16
Pecan Bud Moth 16
Twig Girdler 17
Red-shouldered Shot-hole Borer 17
Flatheaded Borers 17
Obscure Scale 18
Application of Fungicides and Insecticides 18
Spray Equipment 18
Literature Cited 19

SPRAY SCHEDULE FOR THE CONTROL OF PECAN DISEASES AND INSECTS

Name of spray and Insect or Spray materials, Remarks
time of application disease to be per 100 gallon
controlled

Prepollination Scab, downy Zineb,[A] 2 pounds If phylloxera is a
spray, when first spot, vein spot problem, see page
leaves are 14.
one-third grown
First cover spray, Scab, downy Zineb, 2 pounds
when tips of small spot, vein
nuts have turned spot, leaf
brown and nut blotch, brown
casebearer eggs are leaf spot
observed
Pecan nut 3 pounds 50 percent
casebearer, wettable DDT, or 1
pecan leaf pound 25 percent
casebearer wettable parathion,
or 1 pint nicotine
sulfate plus 2
quarts summer oil,
or 5 pounds 40
percent wettable
toxaphene, or 3
pounds 25 percent
wettable malathion
Rosette Zinc sulfate, 2 If rosette is a
pounds problem, include
zinc sulfate in
spray.
Second cover spray, Scab, downy Zineb, 2 pounds
3 to 4 weeks after spot, vein Zinc sulfate, 2
first cover spray spot, leaf pounds
blotch, brown
leaf spot
Rosette
Third cover spray, Scab, brown Zineb, 2 pounds If aphid or mite
3 to 4 weeks after leaf spot, infestations are
second cover spray liver spot, severe, use
aphids, mites insecticides
recommended on page
13.
Walnut If walnut
caterpillar, caterpillars or
fall webworm fall webworms are a
problem, use
insecticides
recommended on
pages 15 and 16.
Rosette Zinc sulfate, 2
pounds
Fourth cover spray Pecan weevil 6 pounds 50 percent For control of
wettable DDT weevils, apply
spray when as many
as three weevils
can be jarred from
a tree. If scab is
present add 2
pounds zineb to DDT
spray.

[A]Zineb. Zinc ethylene bis dithiocarbamate. Manufactured by Rohm & Haas
Co., trade name Dithane Z-78: E. I. DuPont Co., trade name Parzate.

Pecan Diseases and Insects and Their Control

David W. Rosberg and D. R. King

Respectively, associate professor, Department of Plant Physiology and
Pathology, and associate professor, Department of Entomology.

The pecan tree must be protected from attack by the many destructive
diseases and insects that affect it to produce a bountiful nut crop.

The diseases that affect the pecan, especially those caused by fungi,
are rapidly spread throughout the trees in an orchard in the early
spring. During this season of frequent rains, the spores of the disease
fungi germinate and invade the young tender tissues of the shoots,
leaves and nuts. Under conditions of prolonged damp weather, when the
humidity remains high, the disease organisms reproduce at a rapid rate
and cause severe shedding of leaves and nuts.

Pecans are attacked by more than 20 species of insects that cause damage
to leaves, nuts, twigs, buds, branches and even the bark. The
development of commercial pecan acreages has provided ideal conditions
for the increase in severity of both disease and insect damage because
of the abundant food supply in a concentrated planting of pecans. In its
natural habitat the pecan is less subject to the devastations of
diseases and insects.

The many destructive insects and diseases must be controlled for
successful pecan production. The pecan grower must also understand the
nature and habits of the various disease and insect pests that threaten
his crop and use certain cultural practices which help to reduce damage
from diseases and insects.

_Pecan Diseases and Their Control_

The diseases which affect the pecan are of four different types: namely
fungus, bacterial, virus and physiological. The fungus diseases, the
most numerous and widespread, are caused by small microscopic molds.
Approximately 12 different fungus organisms cause harmful diseases of
the pecan.

The bacterial disease organisms, unlike the disease producing fungi, are
single celled and can be seen only under a microscope. Bacterial
diseases are fewer and of less economic importance than fungus diseases.

Virus diseases are caused by extremely small agents which can be seen
only under special ultra-microscopes such as the electron microscope.
Plant viruses are protein substances, but their exact nature is unknown.

Physiological disorders (sometimes called physiological diseases) are
caused by a variety of environmental conditions. A physiological
disorder in a pecan tree may result from infertile soil, excessive
moisture, or the absence or degree of available nutritional mineral
elements to the growing tree. These various environmental factors have
special adverse effects, manifested by specific symptoms caused by
insufficient levels of a given nutritional mineral element or elements,
which are easily corrected by supplying the tree the necessary mineral
elements either through soil application or foliage sprays.

SCAB

Pecan scab, caused by the fungus _Cladosporium effusum_ (Wint.) Demaree,
is the most destructive disease of pecans in Texas. The fungus invades
the young rapidly growing shoots and leaves and later the developing
nuts. Severely infected nuts on highly scab-susceptible varieties fall
or fail to develop, resulting in a total nut crop loss. Early season
defoliation often occurs in seasons of frequent rains and high humidity
which facilitate the rapid development and spread of the scab fungus.

The scab fungus overwinters in infected shoots and in old shucks and
leaves in the trees. In the spring when temperature and moisture
conditions become favorable, the fungus begins to grow in the shoot
lesions, old leaves and shucks, and within a few days produces great
numbers of spores. These spores are spread by wind and rain to newly
developed leaves where they germinate and invade the tender tissues,
initiating primary infection. The fungus produces a great abundance of
spores on the surface of these primary infection sites and spreads
throughout the tree and infects young shoots, leaves and nuts.

On the leaves, primary infection lesions occur on the lower leaf
surfaces and are characteristically olive brown, somewhat elongated in
shape and vary in size from a barely discernible dot to lesions
one-fourth inch or more in diameter. Frequently, adjacent lesions
coalesce, forming large very dark lesions. Primary scab lesions commonly
occur on or along the leaflet veins but often may be found between the
veins on the underleaf surface. On the nuts, scab lesions appear as
small black dots, which are elevated or sunken in older infections.
Adjacent lesions on the nuts may coalesce forming large sunken black
lesions, Figure 1. When infection is severe, the entire nut surface is
black in appearance, development is arrested and the nuts drop
prematurely.

[Illustration: Figure 1. Scab lesions on leaves and nuts of Delmas
variety. Note concave lesions and overall scabby appearance of
severely infected nuts.]

[Illustration: Figure 1. Infected nuts.]

Pecan varieties vary in their susceptibility to scab disease. Among the
highly susceptible varieties are: Burkett, Delmas, Schley, Moore,
Halbert and most western varieties. Moneymaker, Success and Curtis are
moderately resistant. Mahan, Stuart and Desirable varieties are highly
resistant to the scab fungus. However, this character of resistance
varies, depending on the area of the state, local environmental
conditions and the particular strain of the scab fungus present.

Scab disease development is favored by rainy periods and cloudy days
when the humidity remains high and leaf surfaces are wet. Under these
conditions, spores of the fungus in contact with the wet leaf surface of
a pecan leaflet or nut germinate rapidly, invade the tender tissues and
initiate infection within 6 hours. Lesions resulting from these
infection sites, become visible to the naked eye within 7 to 14 days,
depending on environmental conditions. A period of warm dry weather
after infection occurs may retard lesion development.

_Control._—The control of pecan scab disease depends primarily on the
protection of tender leaf, nut and shoot surfaces with proper
application of an effective fungicide. A protective film of fungicide
chemical prevents scab fungus infections by killing the spores
immediately after their germination, thereby preventing invasion of
susceptible tissues. Unfortunately, once the fungus has invaded the
tissues it becomes protected from chemical attack and produces spores in
great abundance. Therefore, thorough coverage of leaf, nut and shoot
surfaces with a fungicide chemical must be maintained to prevent
secondary infections, ([6], [10], [11]).

Sanitation measures, such as removal of old attached shucks and leaf
stems in trees and plowing or disk harrowing under fallen leaves and
shucks help reduce primary infections. See spray schedule, page 4, for
scab disease control.

BROWN LEAF SPOT

The brown leaf spot disease fungus _Cercospora fusca_ (Heald and Walf)
Rand affects only mature leaves and usually does not appear until the
latter part of May or mid-June. Primary lesions develop on the lower
leaf surfaces as small dots, which gradually enlarge and become reddish
brown with a grayish cast. The shape of the lesions may be circular or
irregular, especially where two or more lesions develop adjacent to one
another, Figure 2. In seasons favorable for brown leaf spot development
pecan trees may be completely defoliated within 3 to 4 months if the
disease is not controlled. Most pecan varieties which are maintained in
a vigorous state of growth are resistant to brown spot disease.

_Control._—See spray schedule, page 4.

VEIN SPOT

Vein spot disease is caused by the fungus _Gnomonia nerviseda_. The
symptoms of the disease are similar to the leaf lesion symptoms of scab
disease, but vein spot disease, unlike scab disease, affects only the
leaves. Lesions of vein spot disease develop on the veins or stems of
leaflets and leaves, are usually less than one-fourth inch in diameter
and are characteristically dark brown to black. Leaflets and leaf stems
which are severely affected drop, resulting in premature defoliation.

The fungus lives in fallen leaves over the winter. The following spring
when temperature and moisture conditions are favorable, spores formed in
special structures called perithecia are forcibly discharged into the
air and carried by wind currents to the newly formed spring foliage,
initiating primary infections.

_Control._—See spray schedule, page 4.

LEAF BLOTCH

Leaf blotch disease is caused by the fungus _Mycosphaerella dendroides_
(Cke.) Demaree and Cole. The disease occurs mainly in trees of poor
vigor, which may be due to neglect, infertile soil, rosette or
overcrowding. Nursery trees are particularly susceptible to the disease.

The fungus overwinters in fallen leaves. In the early spring, large
numbers of spores produced in the old leaves on the ground are carried
by wind currents to the young leaves in the tree, where they germinate
and rapidly invade the tender leaf tissue.

The disease symptoms first appear on the undersurface of mature leaves
in early summer, as small olive-green velvety spots. By midsummer black
pimplelike dots become especially noticeable in the leaf spots after the
surface spore masses have been removed by wind and rain, giving the
diseased areas of the leaves a black, shiny appearance. When the disease
is severe, infected leaflets are killed, which causes defoliation of the
trees in late summer or early fall and results in reduced tree vigor and
increased susceptibility to disease and insect attack.

_Control._—Leaf blotch disease can be controlled effectively in the
early spring by disking under old fallen leaves that harbor the fungus
pathogen.

In areas where a spray program for the control of scab disease is
carried out, leaf blotch usually is not a damaging disease. In
localities where leaf blotch disease occurs in the absence of other
pecan diseases, two applications of fungicide will control the disease
effectively. The first spray should be applied after pollination when
the tips of the nutlets have turned brown and the second spray
application should be made 3 to 4 weeks later. See spray schedule, page
4.

CROWN GALL

Crown gall disease, caused by the bacterium _Agrobacterium tumefaciens_
(E. F. and Town.) Conn., often is damaging to pecan trees. Nursery trees
as well as trees in bearing pecan orchards are susceptible to the
disease.

[Illustration: Figure 2. Brown leaf spot diseased pecan leaflet
showing typical symptoms. Lesions are circular to irregular in
shape.]

The development of galls is confined primarily to larger roots near the
base of the tree trunk, although small roots may become infected and
galls develop on them. The smaller galls are under the soil surface and
cannot be detected unless the soil is carefully removed from around the
roots, Figure 3. Large galls, often 10 to 18 inches in diameter, develop
on larger roots and may protrude well above the surface of the soil.

[Illustration: Figure 3. Crown gall disease symptoms on young
infected pecan tree.]

Galls on nursery trees develop at or below the soil surface on the
taproot and larger secondary roots.

_Control._—All infected nursery trees should be dug and immediately
burned. Crown gall-diseased orchard trees sometimes can be saved by
digging the soil from around large roots and removing the exposed galls.
Where galls were removed, the damaged root surfaces should be painted
with a creosote-coal tar mixture (one part creosote to three parts coal
tar) to prevent spread of the disease[9]. Cultivation of the soil around
the trunk base of infected trees should be avoided to prevent root
wounds and spreading of the crown gall pathogen.

DOWNY SPOT

Downy spot disease, caused by the fungus _Mycosphaerella caryigena_
(Ell. and Ev.) Damaree and Cole, attacks all pecan varieties. Only
leaves are susceptible to the disease. Primary infection of new leaves
in the spring occurs from spores produced in specialized fruiting bodies
in old overwintered leaves. The downy spots appear usually during the
summer months on the lower surfaces of leaflets. The downy character of
the lesions is due to the production by the fungus of thousands of
minute spores on the surface of each spot. The spores are spread by wind
and rain to adjacent leaves and to neighboring trees. After spore
dissemination is complete, the lesions visible from both leaf surfaces
are one-eighth to one-fourth inch in diameter and greenish yellow. Later
in the season the lesions turn brown due to the death of the leaf cells
in the diseased area.

Moneymaker and Stuart varieties are most susceptible to downy spot
disease although all pecan varieties are moderately to slightly
susceptible.

_Control._—Disk under old fallen leaves in the early spring before the
leafbuds begin to swell. This practice covers the leaves with soil and
prevents the discharge of spores into the air, thereby controlling
primary infection of new leaves. In seasons when heavy rains make early
spring disking impossible, downy spot disease can be controlled by
spraying the trees as indicated in the spray schedule on page 4.

BUNCH DISEASE

Although the cause of bunch disease is not known, evidence indicates it
is an infectious disease, which suggests that the causal agent may be a
virus.

Trees affected with bunch disease show the bunching symptom, which is
due to excessive growth of slender succulent twigs from lateral buds
that normally remain dormant. In moderately affected trees one or
several branches will show the “bunch” growth symptom. Bunching in
severely affected trees may involve all main branches which produce
thick masses of sucker-like growth and few, if any, nuts.

Observations indicate that the Stuart variety is the most resistant to
bunch disease.

[Illustration: Figure 4. Rosette die-back symptoms of pecan tree
showing severe zinc deficiency.]

_Control._—There is no known effective control for bunch disease. Early
detection of the first symptom of bunch and pruning out of the affected
branch may prevent spread of the disease throughout the tree. When the
tree is severely affected, and limbs are involved, the tree should be
destroyed to protect nearby healthy trees from infection.

For propagation purposes, all bud or scion wood should be taken only
from bunch disease-free trees.

ROSETTE

Rosette is a nutritional deficiency disease caused by certain soil
conditions which make zinc unavailable to the pecan tree. All pecan
trees require zinc for growth.

Trees showing the first symptom of zinc deficiency have yellowed tops.
The individual leaflets when examined are yellowish and mottled. The
next season the foliage may be yellowish and the leaflets narrowed and
crinkled. More severely affected trees produce foliage which is a
yellowish to reddish-brown overall color, and the leaflets are very
narrow with reddish-brown spots and may be perforated. Shoots are much
shortened and the leaves are produced in compact bunches of dense
foliage.

Trees affected by rosette for several seasons have many dead shoots and
small branches from the dying-back of each season’s growth, Figure 4.
Such trees are greatly stunted, of poor vigor and produce few, if any,
nuts.

_Control._—Rosette is controlled readily by applying zinc sulfate to the
tree either as a foliage spray or in the dry form as a soil application.
Where a disease and insect spray control program is being carried out,
zinc sulfate may be added to the spray mixture.

Foliage spray. Two pounds zinc sulfate (36 percent) per 100 gallons of
water.

First application: after pollination when tips of nutlets turn brown.

Second application: 3 to 4 weeks later.

Third application: 3 to 4 weeks later.

Soil application. Application of zinc sulfate to the soil, particularly
in a large orchard is a more expensive operation, but it provides longer
protection against rosette.

In highly alkaline soils, or soils that readily fix zinc and make it
unavailable to the tree, foliage spray applications of zinc sulfate are
more economical because of the excessive rates required to supply
available zinc through the soil.

Rate of application of zinc sulfate: Mildly rosetted trees—apply 5
pounds zinc sulfate (36 percent) annually for 2 to 3 years. Severely
rosetted trees—apply 5 to 10 pounds zinc sulfate (36 percent) annually
until rosette symptoms disappear.

Time and method of application: Apply zinc sulfate to the soil around
trees in late February or early March. Broadcast zinc sulfate under the
tree from the trunk to several feet beyond the limb canopy. Disking,
harrowing, or any operation that mixes the zinc sulfate with the soil,
is desirable to prevent washing away and surface soil fixing of zinc.

LICHENS

Lichens commonly are found growing on the branches and trunks of pecan
trees, especially in humid areas and river bottom orchards having poor
air drainage.

Lichens are nonparasitic to the pecan tree, but merely attach themselves
to the bark surfaces. Lichens grow equally well on rocks, fence posts,
bricks and other objects. There are several types of lichens that occur
on pecan trees, none of which are damaging except perhaps in appearance
to the trees in cases of extremely heavy infestations, Figure 5.

[Illustration: Figure 5. Lichens commonly found on the bark of pecan
trees. Left, a fan-shaped type. Right, an erect-branched type.]

_Control._—The occurrence of lichens in trees regularly sprayed with
copper-containing fungicides is rare.

ARTICULARIA LEAF MOLD

Articularia leaf mold caused by the fungus _Articularia quercina_ (PK)
Hoehn is a disease of minor occurrence and importance. The disease
occurs most commonly following rainy periods and in areas of high
relative humidity in the leaves of trees of poor vigor.

The fungus produces on the lower surfaces of the leaves a conspicuous
growth of white tufts which contain masses of spores, Figure 6.

[Illustration: Figure 6. Articularia leaf mold fungus, showing white
tufts on lower leaf surfaces of pecan leaflets.]

_Control._—Articularia leaf mold does not occur in trees or in orchards
which have been sprayed for disease control.

A single application of fungicide such as zineb at 2 pounds per 100
gallons of water when the disease is first detected is usually
sufficient to control Articularia leaf mold disease.

PINK MOLD

Pink mold, _Cephalothecium roseum_ Corda, usually occurs on nuts
infected with the scab fungus. The pink mold fungus apparently enters
the nuts through scab lesions on the shucks and continues to produce
masses of pink spores on shuck surfaces until late fall. The fungus
sometimes invades the kernel of thin-shelled pecan varieties causing
“pink rot” which is characterized by an oily appearance of the nut shell
and a rancid odor.

_Control._—Pink mold rarely occurs on the shucks of nuts in the absence
of scab disease. In areas where scab disease control is regularly
practiced pink mold is not a problem.

SPANISH AND BALL MOSS

Spanish moss, _Tillandsia usneoides_, and Ball moss, _Tillandsia
recurvata_ L., are not parasitic to the pecan tree and are similar to
lichens in that they both derive their food from the air, rain or
atmospheric moisture.

Neglected orchards in areas of high humidity or poor air drainage are
most troubled with Spanish moss and Ball moss. When large and excessive
growths of Spanish moss develop in pecan trees, the shading effect to
the leaves is detrimental to tree vigor, bearing and growth, Figure 7.

_Control._—The Spanish moss plant like the pecan tree requires sunlight
for vigorous growth. A pecan tree kept in a vigorous state of growth
produces dense foliage that effectively shades accumulations of Spanish
moss and retards its growth.

Spanish moss is not a problem in pecan trees in orchards which are
sprayed with fungicide for disease control. Both Spanish moss and Ball
moss can be controlled by spraying pecan trees with 6 pounds of lead
arsenate per 100 gallons of water[3]. Do not allow livestock to graze in
orchards sprayed with lead arsenate.

COTTON ROOT ROT

Cotton root rot disease is caused by the fungus _Phymatotrichum
omnivorum_ (Shear) Dvgg., a soil-inhabiting pathogen that attacks a wide
range of host plants including the pecan.

The roots of the pecan tree are invaded during the summer when growth of
the fungus in the soil is most active. The infected roots are killed,
disrupting the transportation of water to the leaves, Figure 8. Trees
diseased by cotton root rot produce yellow foliage, and shedding of
leaflets occurs during dry periods. Diseased trees usually die 1 to 3
years after becoming infected.

[Illustration: Figure 7. Spanish moss accumulation in pecan trees
reduces vigor from excessive shading.]

[Illustration: Figure 8. Cotton root infected with cotton root rot
fungus. Note the splitting and general deterioration of the root.]

_Control._—An effective control for cotton root rot disease has not been
developed.

New orchards should not be planted in soil having a history of cotton
root rot disease.

_Pecan Insects and Their Control_

PECAN NUT CASEBEARER

The pecan nut casebearer, _Acrobasis caryae_ Grote, is the major pest of
pecans in Texas. Early in the spring, the overwintered generation feeds
first in the buds and then in the developing shoots, causing them to
wilt and die. Succeeding generations feed on the nuts during the late
spring and summer, Figure 9. Severe infestations may destroy the entire
crop of pecans.

The adult is a light gray moth which is about one third inch in length.
The wings are gray, and the forewings have a ridge of dark scales across
them about one-third the distance from the base. The moths fly at night
and spend the day in concealment.

The young larvae are white to pink, but later become olive gray to green
and attain a length of about one-half inch.

This insect passes the winter as a partially grown larva in a tiny
silken cocoon called a hibernaculum, which is usually attached to a bud,
Figure 10. In the spring, the larvae feed for a short time on the buds,
after which they tunnel in the developing shoots until they reach
maturity, Figure 11. Pupation usually occurs in these burrows, and the
moths emerge in late April and May.

Two or 3 days after the adults emerge, they deposit eggs on the tips of
the nuts, Figure 12. Each female may deposit from 50 to 150 eggs. The
eggs, which are just visible to the naked eye, are greenish white when
they are deposited but assume a reddish appearance a few days later. The
first-generation larvae hatch from the eggs in 4 or 5 days and migrate
to the buds below the nuts to feed. After a day or two, they enter the
nuts, usually at the base, and feed in them, each larva frequently
destroying an entire cluster. Bits of frass and webbing may be observed
projecting from the injured nuts. Upon reaching maturity, the larvae
pupate in the nuts and emerge as adults in June and early July.

[Illustration: Figure 9. Injury to nuts caused by first generation
larvae of the pecan nut casebearer.]

The adults deposit eggs in grooves on the tips or bases of the nuts.
Second-generation larvae which hatch from these eggs also feed in the
nuts. Less injury is produced by this generation because the nuts are
larger and each larva requires only one or two nuts to complete its
development. Pupation takes place in the hollowed out nuts, Figure 13,
and the moths emerge from late July to early September.

A third generation usually follows, but the shells of the nuts have
become hard, and only a few of them are penetrated by the larvae.
Instead, they feed in the shucks. A number of third-generation larvae
construct hibernacula, while the remainder pupate and appear as adults,
emerging from late August to October. These adults deposit eggs, which
hatch into fourth-generation larvae. If nuts are available, their shucks
constitute the principal food of the larvae of this generation. In the
absence of nuts, the larvae feed on buds and leaf stems. Overwintering
hibernacula are constructed by the partially grown larvae by the middle
of November[2].

_Control._—The necessity for control of this pest may be determined by
examination of the trees when the shoots appear in the spring. If a
number of them are wilted, the following control measures probably will
be required.

A spray application should be made when eggs of the first generation
appear on the tips of the young nuts in late April or May. The period of
egg deposition usually coincides with the completion of pollination, at
which time the tips of the nuts turn brown. Satisfactory control may be
obtained by using any of several insecticides. See spray schedule, page
4.

Ordinarily, only one application of spray is required to control the nut
casebearer. However, if trees surrounding the treated area are not
sprayed, moths may enter the sprayed area and a serious infestation of
second-generation larvae may develop. Under these circumstances, a
second spray may be required in June or early July when
second-generation eggs are deposited[6], [11].

HICKORY SHUCKWORM

The hickory shuckworm, _Laspeyresia caryana_ (Fitch), frequently causes
severe injury to pecans. In the late summer and fall the shucks are
tunneled out. As a result, the nuts are slower to mature and the kernels
do not develop properly. The shucks stick to the nuts and fail to open,
thus increasing the difficulty of harvest.

The adult shuckworm is a dark, grayish-black moth with a wing span of a
little over one-half inch. The larva is white with a light brown head.
It attains a length of three-eighths inch at maturity.

The winter is passed by the larvae in fallen pecan or hickory shucks.
They pupate in late winter and emerge as adults during the spring. The
adults deposit eggs principally on hickory trees on the leaves and young
nuts, and the larvae feed in developing nuts in early summer.

Succeeding generations develop in pecan shucks. Before pupating, the
larvae cut a hole to the outside, and then spin a cocoon. When the moth
emerges, the empty pupal skin is left projecting from the hole and can
be seen afterward on the shuck. As many as five generations may be
completed each year before the last generation larvae go into
hibernation.

_Control._—No economical chemical control for the shuckworm has been
developed. Cultural measures will aid in reducing populations. Plowing
during July and August to turn under the infested shucks is relatively
effective. The larvae are unable to mature in the decaying shucks, and
the adults cannot emerge from the soil. Care should be taken to
completely cover the fallen shucks, but the depth of plowing should be
regulated or damage to the roots will result.

[Illustration: Figure 10. Location of overwintering cocoons, or
hibernacula, of the pecan nut casebearer.]

PECAN WEEVIL

The pecan weevil, _Curculio caryae_ (Horn), is a late-season pest of
pecans in Texas. In years when severe infestations occur, this insect
may destroy a large portion of the pecan crop. The kernels are eaten out
by the larvae.

The adult is a brownish weevil which is about three-eighths inch long.
The female has a snout which is as long as the body; the male’s is
somewhat shorter.

The weevil appears in late August and early September. After the nut
kernels have hardened, the female chews a hole in the shell and deposits
her eggs in little pockets in the nuts. Creamy white grubs hatch from
the eggs and feed inside the nuts during the fall, attaining a length of
about three-fifths inch. When they reach maturity, the grubs chew a hole
about one-eighth inch in diameter in the shell, emerge from the nut and
drop to the ground in late fall and early winter. They burrow in the
soil to a depth of 4 to 12 inches and construct a cell. Some individuals
remain in the larval stage until the following fall when pupation
occurs. Other larvae do not transform to pupae until the succeeding
year. The adults appear during the summer, following pupation. The
entire life cycle requires from 2 to 3 years, most of this time being
spent in the soil.

[Illustration: Figure 11. Overwintered larva of the pecan nut
casebearer and characteristic injury to the developing shoots.]

_Control._—Frequently, certain trees in the orchard are more heavily
infested than others, since the adults usually do not go far from the
tree upon which they developed. The time at which insecticide
applications should be made to control this insect can be determined by
jarring the trees. Begin checking the first week in August. A large
sheet should be placed under a tree and the limbs jarred with a padded
pole. The weevils drop to the ground and remain motionless for a short
period, at which time they may be counted. When three or more weevils
are jarred from each tree, an application of spray containing 6 pounds
of 50 percent DDT wettable powder per 100 gallons of water should be
made[8].

[Illustration: Figure 12. Eggs of the first generation pecan nut
casebearer deposited on the tips of the young nuts.]

STINK AND PLANT BUGS

The adults of several species of stink bugs and plant bugs suck the sap
from young pecan nuts causing an injury known as black pit, in which the
interior of the nuts turns black. The injured nuts fall from the trees
before the shells harden.

Feeding by the insects after shell hardening, Figure 14, produces brown
or black spots on the kernels. Areas affected taste bitter, but the
remainder of the kernel is unaffected.

Stink bugs are familiar to everyone. Plant bugs resemble them and are
usually shades of brown, smaller and narrower in body outline.

Plant bugs and stink bugs overwinter in the adult stage in debris on the
ground. In the spring, the adults are attracted to growing vegetation
such as cover crops or weeds, where they deposit their eggs. The
immature bugs develop on low-growing vegetation. When they reach
maturity, their wings are fully developed and they fly to pecan trees. A
few eggs may be deposited on pecan trees, but the young bugs apparently
are unable to develop on them. Only the adults are present in sufficient
number to inflict economic injury. There may be as many as four
generations each year.

_Control._—Although certain insecticides will control these pests, the
number and frequency of spray applications necessary for control would
not be economical.

Care should be taken to keep weeds down in the orchard during the
growing season. Winter cover crops should be plowed down early in the
spring so they will not be attractive to the adults coming out of
hibernation. If this operation is delayed, the bugs will leave the cover
crop when it is removed and migrate to the trees in large numbers.

APHIDS

These soft-bodied insects appear during the summer and fall. They suck
the sap from the leaves, causing them to turn yellow or brown and fall
to the ground. Heavy infestations may cause defoliation in the late
summer reducing the nut crop in the current and succeeding year.

The black pecan aphid, _Melanocallis caryaefoliae_ (Davis), is about
one-sixteenth inch long when full grown, robust and greenish black. Its
back is decorated with tubercles.

Bright yellow blotches up to one-fourth inch in diameter appear around
the punctures produced by the feeding of this insect.

The yellow aphids, _Monellia_ spp., which attack pecans inflict injury
similar to that caused by the black pecan aphid. However, the large
yellow blotches on the leaves do not result from their feeding. A sticky
substance called “honeydew” is secreted by these insects creating an
ideal medium for sooty mold fungus to develop[5].

Both black and yellow aphids overwinter in the egg stage in crevices in
the bark. In the spring the eggs hatch, and the aphids begin feeding on
the leaves. Many generations are completed each year. Only females,
which may be wingless or winged, are produced during the growing season.
The winged individuals fly to different parts of the tree or to other
trees. In the fall, males and females appear and eggs are deposited
under the bark.

[Illustration: Figure 13. Pupa of the second generation of the pecan
nut casebearer in a hollowed out nut.]

Usually, these insects are not present in sufficient numbers to cause
serious injury until mid or late summer. Infestations earlier in the
season rarely assume damaging proportions. As is the case with mites,
aphid populations may increase, following the application of certain
insecticides applied for the control of the pecan nut casebearer or
following treatment with bordeaux mixture for pecan scab disease
control.

[Illustration: Figure 14. Southern green stink bug on developing
nuts.]

_Control._—When damaging infestations appear, the trees should be
sprayed with either 1 pound of 12 percent gamma BHC wettable powder; or
1 pint of 40 percent nicotine sulfate plus 3 pounds of soap; or 1 pound
of 25 percent parathion wettable powder[9].

MITES

These tiny pests attack the leaves usually on the underside causing
irregular brown areas to appear. Trees which are heavily infested appear
scorched and may lose their leaves in late summer or fall.

Mites usually are light green and are just large enough to be seen
without the aid of a hand lens. They are wingless and feed principally
on the underside of the leaves along the midrib. Colonies of them
produce webs in which molted skins and eggs may be found. The life cycle
of mites is very short and several generations occur each year. Large
populations may develop during the late summer and fall.

The use of certain insecticides for the control of the pecan nut
casebearer or bordeaux mixture for scab control frequently contributes
to increases in mite populations later in the season.

_Control._—Mites may be controlled in three ways when damaging
infestations develop. An application of 2 pounds of wettable sulfur per
100 gallons of water may be made; 6 pounds of wettable sulfur per 100
gallons of water may be added to the spray applied for the control of
the nut casebearer; and repeated applications of zineb included in a
regular spray schedule for pecan scab control will effectively control
mites. However, a single application of zineb is not effective[7].

PECAN LEAF CASEBEARER

On occasion, this insect, _Acrobasis juglandis_ (LeB.), develops to
damaging numbers and causes economic injury. Early in the spring the
larva feeds on unfolding leaves and buds. It may prevent leaf
development for weeks, resulting in a greatly decreased yield of nuts.

The adult is a dark gray moth marked with brown. Its forewings, which
have a spread of about two-thirds inch, are gray with black blotches.
There is a reddish mark near the base of the forewings.

The immature larva is brown, but changes to dark green as it develops to
a length of one-half inch. It has a shiny, brownish black head and is
enclosed in a gray case which completely covers the body and is borne in
a position nearly perpendicular to the leaf on which the larva is
feeding.

The pecan leaf casebearer overwinters as an immature larva in a
hibernaculum around a bud. It emerges in late March or early April as
the buds open. The larvae mature in April, May and June and transform
into pupae within their gray cases, Figure 15. The moths are present
from May until early August. Eggs are deposited during this period on
the underside of the leaves. The larvae which hatch from these eggs
develop slowly, and do not attain a length of more than one-sixteenth
inch during that season. They construct little winding cases in which
they live. Their feeding produces irregular blotches on the leaf
surface, Figure 16. Before the leaves drop in the fall, the larvae
migrate to the buds, and construct their overwintering hibernacula. Only
one generation is completed each year.

_Control._—Control of this insect is accomplished by spraying for the
pecan nut casebearer. See spray schedule, page 4. The insecticides
recommended for nut casebearer control also reduce infestations of the
leaf casebearer.

[Illustration: Figure 15. Overwintered larvae of pecan leaf
casebearer in their cases.]

[Illustration: Figure 16. Summer injury to the leaves by the pecan
leaf casebearer.]

PECAN PHYLLOXERA

The pecan phylloxera, _Phylloxera devastatris_ Perg., and the pecan leaf
phylloxera, _P. notabilis_ Perg., produce galls on the new growth of
pecans. Leaves, twigs and nuts may be affected.

The galls are conspicuous swellings, Figure 17, which attain a size of
from one-tenth to 1 inch in diameter. They are caused by a soft-bodied
insect which is closely related to aphids.

The winter is passed in the egg stage in crevices in the bark. In the
spring, the egg hatches and the tiny nymph feeds on the tender, young
growth, apparently secreting a substance which stimulates the plant
tissues to develop into galls.

After the nymph reaches maturity, a number of eggs are deposited inside
the gall. The young nymphs of the succeeding generation develop within
the gall, which splits open in 1 to 3 weeks, liberating them. Several
generations follow during the summer and fall, as long as there is fresh
young growth on the tree. From 4 to 5 weeks are required for each
generation[4].

_Control._—The dormant oil spray recommended for obscure scale control
will prevent the development of phylloxera. If dormant oil is not
applied, use 2 pints of nicotine sulfate plus 6 pounds of soap; 3 pounds
of 25 percent malathion wettable powder; or two and a half pounds of 10
percent gamma isomer BHC wettable powder per 100 gallons of water when
the leaves are one-third grown.

SAWFLIES

Sawfly larvae, _Periclista_ sp. and others, feed on the foliage of
pecans during April and early May. The larvae, which are light green,
chew holes in the leaves. Usually the midrib and veins are left intact,
giving the leaflets a lacy appearance, Figure 18.

The adults closely resemble wasps, except that they are not
“wasp-waisted.”

[Illustration: Fig. 17. Developing galls of the pecan phylloxera.
Note the open gall on the lower leaf.]

_Control._—The larvae may be controlled with an application of 2 pounds
of 50 percent DDT wettable powder or 1 pound of 25 percent parathion
wettable powder per 100 gallons of water.

[Illustration: Figure 18. Sawfly injury to pecan foliage.]

MAY BEETLES

Many species of May beetles may damage pecans early in the spring. The
beetles appear only at night and spend the day concealed beneath the
surface of the soil. They feed on the young leaves and prevent the
foliage from developing.

Beetles of the most common species are one-half to three-fourths inch
long and shiny dark brown. They are attracted to lights and are observed
commonly on porches or screen doors at night. The larvae are the
grubworms, or white grubs, which feed in the soil on the roots of many
plants.

The female beetle deposits eggs in the soil, where the larva develops.
Most species require two summers for the larva to mature. Pupation is
accomplished in a cell which is constructed in the ground in the fall of
the second year. The beetles emerge the following spring. Both larvae
and adults may be found in the soil during the winter.

_Control._—May beetles are usually a problem in orchards which are not
cultivated because the larvae feed on the roots of the sod cover.
Cultivation of the orchard periodically will reduce the food supply of
the grubs, and smaller infestations of adults will appear the following
year. Where cultivation is not feasible, sprays will control the adults.
Apply 2 pounds of 50 percent DDT wettable powder; 4 pounds of lead
arsenate; or 1 pound of 25 percent parathion wettable powder per 100
gallons of water when damage by this insect is severe[9].

PECAN CIGAR CASEBEARER

The pecan cigar casebearer, _Coleophora caryaefoliella_ (Clem), may be
damaging in some years. The larva feeds on the leaves, producing tiny
holes. It constructs a light brown, cigar-shaped case about one-fourth
inch in length which encases it throughout development.

_Control._—The spray applied for control of the nut casebearer will
usually prevent significant injury by the cigar casebearer. See spray
schedule, page 4.

FALL WEBWORM

The webs produced by the fall webworm, _Hyphantria cunea_ (Drury), are
familiar to everyone. Leaves are eaten by the larvae which live in
loosely woven, dirty white webs, Figure 19.

The adult is a white moth which may have black or brown spots on the
forewing. Its wings have a span of about 1 inch.

The larvae are pale yellow spotted with black. They attain a length of 1
inch when full grown and are covered with long black and white hairs.

The insect overwinters as a pupa in lightly woven cocoons in debris on
the soil or under the bark. In the spring the adults emerge and lay
masses of greenish white eggs on the leaves. The caterpillars which
hatch from the eggs feed on the leaves in colonies under webs which they
construct. After feeding for a month to 6 weeks, the larvae crawl down
the tree and pupate in loose cocoons in debris, under bark, or in loose
soil. Adults appear during the summer and deposit eggs for the second
generation. The larvae of this generation feed extensively until fall,
crawl down the tree and pupate for the winter.

_Control._—Light infestations on a few trees can be eliminated by
pruning out the affected branches and burning them. If this method of
control is not practicable, the trees should be sprayed with 2 pounds of
50 percent DDT wettable powder; 1 pound of 25 percent parathion wettable
powder; or 3 pounds of lead arsenate per 100 gallons of water[9].

[Illustration: Figure 19. Web of the fall webworm on a pecan limb.]

WALNUT CATERPILLAR

During the spring and summer, the walnut caterpillars, _Datana
integerrima_ G. & R. and others, may strip the leaves from branches or
entire small trees. The adult is a moth with a wingspan of 1½ to 2
inches. The forewings are light brown with darker wavy lines. The
hindwings are lighter in color without lines.

The immature larva is reddish brown with narrow yellowish lines that
extend the length of the body. The full-grown larva is almost black with
two grayish lines on the back and two on the sides. Many long, soft gray
hairs are distributed over the body.

This insect overwinters in the pupal stage in the soil. The adult
emerges in the spring and deposits eggs in masses on the underside of
the leaves, Figure 20. The larvae feed in colonies on the leaves for
about 3 weeks. At periodic intervals, the groups of larvae move to the
trunk to molt and, after shedding their skins, they return to the leaves
to feed until the next molt. They do not encase themselves in webs.
There are two generations each year, the first appearing in late spring
and early summer, the second in later summer and fall. Larvae of the
second generation complete development and crawl down to pupate in the
soil.

_Control._—When these insects become abundant enough to defoliate
portions of the tree, they may be controlled by applying a spray
containing 2 pounds of 50 percent DDT wettable powder; 3 pounds of lead
arsenate; or 1 pound of 25 percent parathion wettable powder per 100
gallons of water.

[Illustration: Figure 20. Walnut caterpillar adults and egg mass on
a pecan leaflet.]

PECAN CATOCALA

Several species of catocalas, Figure 21, among them _Catocala maestosa_
Hlst., may strip the leaves of pecans in the spring leaving only the
midribs. The caterpillars are very dark gray and attain a length of
about 3 inches when full grown. They are very active when disturbed and
move with a looping motion. Both the caterpillars and the moths are well
camouflaged. When they rest on the trees during the day, their color so
harmonizes with the color of the bark that they are frequently
indistinguishable.

_Control._—One application of 2 pounds of 50 percent DDT wettable powder
per 100 gallons of water controls this pest. Although the majority of
catocala larvae reach maturity before the time to spray for the nut
casebearer, a number of them will be killed when the recommended spray
is applied for the latter insect.

PECAN SPITTLEBUG

In the spring and early summer a number of buds and small nuts may be
covered with foamy white masses. Inside these masses are several small
insects called spittlebugs, _Clastoptera obtusa_ (Say). The white froth
is produced probably to maintain an artificial high humidity, which is
required for development. The adults resemble leafhoppers and fly
actively during the summer.

This insect has not been known to cause any significant injury on pecans
in Texas.

PECAN BUD MOTH

The pecan bud moth, _Gretchena bolliana_ (Sling.), damages nursery stock
and freshly top-worked pecans. The greenish larvae feed in the axils of
the newly set buds and in the terminals of young trees, causing
extensive branching. There are several generations each year.

[Illustration: Figure 21. Moth of the pecan catocala.]

_Control._—This insect may be controlled by applying a spray containing
2 pounds of 50 percent DDT wettable powder per 100 gallons of water.

TWIG GIRDLER

The adult twig girdler, _Oncideres cingulata_ (Say) (_O. texana_ of some
authors), girdles twigs and branches, weakening them so that they fall
off or die on the tree, Figure 22. This insect is active during the late
summer and early fall. Many twigs may be found on the ground under a
severely infested tree. Secondary branching may occur and the number of
bearing twigs is reduced.

The twig borer is a grayish brown beetle one-half to five-eighths inch
in length with a broad gray band over the middle of the wing covers. Its
head is reddish brown and bears a pair of long antennae, which extend
beyond the abdomen on the male.

The larva is a white legless grub about three-fourths inch long when it
reaches maturity.

This insect overwinters as a partially grown larva in a twig on the tree
or ground. It develops rapidly in the spring feeding in the twig.
Following pupation, the adult emerges in late August or early September.
The female systematically girdles twigs and deposits eggs in the severed
portion since the larva is unable to develop in healthy sapwood. The
eggs hatch in a few weeks into larvae which remain small until the
following spring when they complete development, pupate and emerge as
adults in the late summer and fall. There is one generation annually,
although some individuals require 2 years to mature[1].

_Control._—Infestations may be reduced by removing girdled branches from
the trees and the ground and burning them.

Chemical control is also effective. The trees should be sprayed with 4
pounds of 50 percent DDT wettable powder per 100 gallons of water when
the first injured branches are observed in late August or early
September. Two or three applications at 2-week intervals may be required
for most effective control[9].

RED-SHOULDERED SHOT-HOLE BORER

The red-shouldered shot-hole borer, _Xylobiops basilare_ (Say), and
other shot-hole borers also injure trees in a devitalized condition. The
larvae feed in wood, pupate and emerge as adults through round holes
about one-eighth inch in diameter in the bark. Many of these holes may
be observed in close proximity to each other.

_Control._—Since this insect feeds on dying or dead wood, prunings and
dead limbs should be removed from the orchard and burned.

Adequate fertilizer and water will keep trees in a healthy condition and
prevent injury by this pest.

FLATHEADED BORERS

The flatheaded apple tree borer, _Chrysobothris femorata_ (Oliv.), and
other species of flatheaded borers attack unhealthy or recently
transplanted pecan trees by burrowing in the bark and sapwood of the
large branches and trunk. Their presence is indicated by the appearance
of darkened, depressed areas in the bark from which traces of frass may
protrude. When these portions of the bark are removed, shallow winding
burrows packed with sawdust may be observed. The burrows usually are on
the sunny side of the trunk or branch, but may extend completely around
and penetrate the wood to a depth of 2 inches. Young trees may be
girdled by this insect.

The adult beetle is about one-half inch long, broad and blunt at the
head end and tapering to a point posteriorly. Its wing covers, which
have a metallic sheen, are dark colored and corrugated.

The larva, or borer, which is legless and yellowish white, attains a
length of 1¼ inches when full grown. Immediately behind the head is a
broad, flattened expanded area from which the insect takes its name.

The winter is passed by larvae in varying stages of development within
the tree. In the spring, they change to pupae in their burrows, emerging
as adults during the spring and summer. The female beetles deposit their
eggs in cracks or bruises in the bark. The larvae which hatch from these
eggs feed during the remainder of the season and pass the winter. There
is only one generation each year.

[Illustration: Figure 22. Adult twig girdler and characteristic
injury to twig.]

_Control._—The beetles are attracted to trees or areas of trees in a
devitalized condition, induced by transplanting, drouth, sunscald,
bruises or poor growing conditions. The trees must be kept in a healthy,
vigorous condition by proper fertilization and watering. On young or
transplanted trees, wrapping the trunks in early spring before the
adults appear is the only effective control known for these insects.
Injury can be prevented by thoroughly wrapping the entire trunk from
ground level to the branches with heavy paper or other wrapping
material. The wrapping should be tied securely with twine and should be
maintained on the tree for 2 years. Regular observations should be made
to see that the twine does not girdle the tree.

In older trees, the borers can be removed with a sharp knife. Care
should be taken to injure as little of the healthy wood as possible. If
the wound is extensive, it should be trimmed and then painted with a
commercial tree paint or with a mixture of one part creosote and three
parts coal tar. Dead and dying limbs and trees should be removed from
the orchard each year and burned before the following spring. If they
are not burned, the borers in them may mature and re-infest surrounding
trees. Commercial tree borer preparations are of little value in
controlling this insect.

OBSCURE SCALE

The obscure scale, _Chrysomphalus obscurus_ (Comst.), is a pest of
considerable importance, particularly in the more arid portions of the
State. The tiny insect under its scale covering sucks the sap from the
limbs and branches, causing them to lose their leaves and die back from
the tips. The tree is so devitalized by the feeding of this insect that
it is made vulnerable to attack by wood borers.

The scale covering over a full-grown female is about one-eighth inch
long and is usually dark gray, and closely resembles the bark of the
tree. Infested limbs appear to have had wood ashes sprinkled over them,
Figure 23. Numerous pits appear in the bark where the insects feed,
producing a roughened appearance.

[Illustration: Figure 23. Severe infestation of obscure scale on a
pecan twig.]

The winter is passed by the female scales under their coverings on the
bark. Eggs laid in the spring hatch into tiny, salmon-colored crawlers
which move about for a short time, then settle down and insert their
beaks. While they are feeding, a scale covering develops which is made
up of secreted wax and cast skins.

The females never move again from the spot they have selected, but the
adult males develop wings and emerge from their scale coverings to mate
with the females. Only one generation is produced each year.

_Control._—When damaging populations develop, a spray application of 3½
gallons of 97 percent miscible dormant oil per 100 gallons of water
during the dormant season will keep this pest under control.

_Application of Fungicides and Insecticides_

When possible, fungicides for disease control and insecticides for
insect control should be combined in the spray tank and applied to the
trees in one operation. The spray materials should be applied evenly and
thoroughly to all the leaf and nut surfaces to provide a chemical
barrier to disease organisms and insects. Do not neglect the tops of the
trees. Diseases and insects can harbor and multiply in all unsprayed
areas of the tree.

Thorough coverage with spray materials is essential for effective
control. As a guideline, apply approximately 1 gallon of spray mixture
for each foot of tree height. Apply 20 gallons to a 20-foot tree and 40
gallons to a 40-foot tree, etc.

_Spray Equipment_

Various types of spray machines for application of fungicides and
insecticides to pecan trees are available. The spray machines employ
either a high pressure hydraulic pump, high pressure centrifugal pump or
low pressure high air velocity systems. All the machines are portable
and are equipped with a gasoline engine or operate from a truck or
tractor power takeoff shaft.

For pecan spraying, a tank having a minimum capacity of 300 gallons is
desirable. The pump should deliver 20 to 30 gallons per minute and
maintain a pressure of 400 to 600 pounds per square inch while
operating. A spray gun which is adjustable to produce a mist spray for
spraying small trees or the lower canopy of large trees and a narrow
stream that will reach the tops of tall trees is essential.

For safety and durability high pressure rubber hose having an inside
diameter of three-fourths inch should be used with all high pressure
spray machines.

_Literature Cited_

[1]Bilsing, S. W., 1916; Life history of the pecan twig girdler. Journal
Econ. Ent. 9:110-115.

[2]Bilsing, S. W., 1927; Studies on the biology of the pecan nut
casebearer. Texas Agricultural Experiment Station Bulletin 347, 71
pp.

[3]Bilsing, S. W., 1941; An economical method of removing Spanish moss
(_Tillandsia usenoides_) and Ball moss (_Tillandsia recurvata_) from
trees. Texas Agricultural Experiment Station Progress Report 747.

[4]Dobbins, Traber Norman, 1932; The biology of the pecan phylloxera.
Master’s Degree Thesis, Texas A. and M. College.

[5]Dorman, Harvey S., 1934; The life history of the yellow pecan aphid
_Monellia nigropunctata_ Granovsky. Master’s Degree Thesis. Texas A.
and M. College.

[6]King, D. R. and David W. Rosberg, 1955; Experiments for the control
of pecan insects and diseases, 1954. Texas Agricultural Experiment
Station Progress Report 1786.

[7]King, D. R. and David W. Rosberg, 1956; Control of _Tetranychus
hicoriae_ McG. on pecans. Journal Econ. Ent. 49 (3):404-5.

[8]Nickels, C. B., 1952; Control of the pecan weevil in Texas. Journal
Econ. Ent. 45 (6): 1099-1100.

[9]Osburn, M. R., A. M. Phillips, William C. Pierce, and John R. Cole,
1954; Insects and diseases of the pecan and their control. USDA
Farmers Bulletin 1829, 56 pp.

[10]Rosberg, David W., 1950; Control of pecan diseases in 1950. Texas
Agricultural Experiment Station Progress Report 1330.

[11]Rosberg, David W. and D. R. King, 1954; Pecan disease and insect
control experiments in Texas, 1953. Texas Agricultural Experiment
Station Progress Report 1671.

_Your County_ EXTENSION AGENTS

[Illustration: Extension agents]

can furnish you the latest information on farming, ranching and
homemaking. They represent both The Texas A. & M. College System and the
United States Department of Agriculture in your county.

Most county extension agents have their offices in the county courthouse
or agriculture building. They welcome your visits, calls or letters for
assistance.

This publication is one of many prepared by the Texas Agricultural
Extension Service to present up-to-date, authoritative information,
based on results of research. Extension publications are available from
your local agents or from the Agricultural Information Office, College
Station, Texas.

Cooperative Extension Work in Agriculture and Home Economics. The Texas
A. & M. College System and United States Department of Agriculture
cooperating. Distributed in furtherance of the Acts of Congress of May
8, 1914, as amended, and June 30, 1914.

10M-3-59. Reprint.

Transcriber’s Notes

—Silently corrected a few typos.

—Retained publication information from the printed edition: this eBook
is public-domain in the country of publication.

—In the text versions only, text in italics is delimited by
_underscores_.

*** End of this LibraryBlog Digital Book "Pecan Diseases and Pests and Their Control" ***

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