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Text from M. A. Harris and J. A. Jackman.
1991. Pecan Arthropod Management. pp. 6-15. In B. W. Wood and J. A.
Payne (eds.). Pecan Husbandry: Challenges and opportunities. First
National Pecan Workshop Proceedings. U.S. Dept. of Agriculture,
Agriculture Research Service, ARS-96.
INTRODUCTION
Pecan arthropod management practices today are a legacy inherited
from our predecessors stretching back in time more than 4,000 years
to "when the Sumerians used sulfur compounds to control insects and
mites" (Bottrell 1979). Pest control by manipulation of natural
enemies, application of chemicals, and the use of physical and
cultural methods all originated before the Christian era. Human
ingenuity and time have combined to provide us the tools we presently
use to minimize the adverse effects pest arthropods can have on food
and fiber production and storage. Despite these massive, extensive
and creative efforts, we are still routinely plagued by pest
arthropods. Events within the past decade involving Medfly,
Ceratitus capitata; Africanized honey bee (so-called killer
bees), Apis mellifera; and ticks that vector Lyme disease
illustrate our continuing vulnerability to pest arthropods.
A prime example in the pecan industry occurred in 1985 when the
Federated Pecan Growers Association declared pecan aphids to be the
number one pest and noted that the problem was so severe that the
entire industry could fail if the aphids could not be dealt with
effectively. The primary point here is that pest arthropods
consistently pose difficult challenges to human progress throughout
our culture and, pecan production, despite technological advances,
continues to suffer its share of problems from pest arthropods as
well.
The reasons for these continuing difficulties are many, but two
factors address the core of the problem. The majority of arthropod
pest problems are both complex and dynamic. Complexity means that
solutions are hard to come by and a dynamic quality implies today's
solution may not solve tomorrows problem. In fact, today's solution
may actually cause tomorrow's problem. This is especially true where
living organisms are involved. Those capable of surviving changes in
their environment confer these capabilities to their offspring
thereby allowing just a few survivors of, say, pesticide treatments,
to give rise to an entire, epidemic level, population of
survivors.
Another kind of complexity is introduced by increased involvement
and concern by the public, expressed both through laws and
supermarket purchases, in how pest and other problems are solved. The
alar controversy is one example and the removal of phosalone from
pecan is another. Chemical agriculture will be less dependable in the
future for this reason as well.
The resolution of pecan arthropod problems in production
agriculture can only be accomplished by developing an understanding
of this complex system and by anticipating how that system will be
affected by specific solutions. The approach taken by the Pecan
Insect Laboratory at Texas A&M University is to compare and
contrast the survival mechanisms inherent in the unmanaged pecan with
the production requirements placed on the commercial pecan (Harris
1980). This allows us to examine how pecan interacts and survives
with arthropods in natural situations and then to focus on how and
why particular arthropods achieve pest status in commercial
situations. This broad perspective provided useful insights that
resulted in effective management approaches in this complex and
dynamic system. Although much progress has been made, primarily
through the Southern Regional Project on Pecan Arthropods, in which
my lab participates, we have only begun to understand the complex and
dynamic features of this agroecosystem, and to convert that knowledge
to management approaches that result in greater quantities of high
quality reasonably priced pecans available to consumers everywhere
throughout the year and provide a fair return to the producers. The
purpose of this paper is to take a broad view of pecan arthropod
management in the context of pecan production and to attempt to
anticipate problems and consider options from a wider perspective
than is usually taken.
PECAN DEFENSES AGAINST THE PECAN PEST COMPLEX
There are five defense mechanisms whereby a plant species can
survive phytophagy and these can be expressed from the subcellular to
the individual to the population level of organization. These
mechanisms are escape in space, escape in time, confrontation,
accommodation, and biological associations (Harris 1980). These
defenses allow transmission of superior phenotypes from one
generation to the next by natural selection (Grant 1977).
Pecan utilizes all these mechanisms in the natural environment and
what little is known has been reviewed elsewhere (Harris 1980, 1988).
A principal feature for pecan is masting (synchronous nut production
over wide areas at irregular intervals) to escape primary nut feeders
by periodic satiation and starvation. Confrontation of pests like
pecan phylloxera and pecan scab is a population phenomenon where
individual trees may succumb but the diverse population is protected
from an epidemic (Browning 1980; Harris 1980). Accommodation of
foliage feeders by universal susceptibility to periodic defoliators
like walnut caterpillar and to some extent, aphids, preserves the
masting cycle for the pecan and natural enemies keep the pest in
check most of the time (Harris 1980).
The selection and vegetative propagation of annually productive
pecan in large genetically uniform monocultures drastically reduces
mechanisms for escape in space and time and eliminates
confrontational mechanisms based on population diversity. Protection
with broad spectrum pesticides eliminates many favorable biological
associations and supplemental fertilization and irrigation improves
nutritive quality and extends windows of susceptibility to pests that
could otherwise be escaped, confronted or accommodated. Pecan
arthropod management programs have largely developed in a reactive
capacity without providing input on long range development plans for
the industry. Given that a failure to solve pest problems can
eliminate a crop from a wide production area, i.e., sugar beets,
sugar cane, cotton and sunflower have all been driven from production
from some areas due to pests, a production system that does not
capitalize on all natural defense mechanisms compatible with
commercial production may increasingly risk failure. Greater
attention needs to be paid to the limited information available in
this area and further work should be supported to identify and
capitalize upon risks and rewards using this approach.
PECAN HISTORY
Carya illinoensis (Wang) K. Koch is native to North America
from the Mississippi River Valley to West Texas and into Mexico
(Little 1971). Brison (1974) notes the pecan is the most important
horticultural crop native to the United States. The American Indian
relied on pecan nuts nature provided for food; but, serious
domestication of the tree really began when early settlers thinned
wild mixed species stands of trees to leave some pecan and create a
pasture understory for cattle (Table 1). The earliest orchards were
established by seed followed by development of vegetative
reproduction technology in the middle of the last century allowing
the "best" varieties to be propagated wherever the trees would grow.
This technology and an entrepreneurial spirit resulted in an
extensive expansion of the pecan industry into the southeastern U.S.
in the early 1900s and to the west of the Pecos in the 1930s and
continuing to the present. Conversion from thinned stands of wild
pecan to vegetatively propagated orchards in the native range was
very slow because nuts produced by wild trees were and are
competitive with those from improved varieties.
Native pecan producers are reluctant to remove producing trees,
even those a century old or more, and plant an orchard in their place
because of 1) the initial expense, 2) the time required to recoup
that investment from new production, 3) the change in lifestyle from
a cattle/pecan mixed agriculture system to pecan monoculture, and 4)
other uncertainties in such a long-lived crop like fluctuating prices
and revisions of tax law. Consequently, about 50% of the 300 million
lbs. of pecan nuts produced annually in the U.S. come from trees
nature planted or grown from seedlings, with the remainder produced
primarily from a dozen or so of the 1,000 plus vegetatively
propagated "cultivars" noted by Thompson and Young (1985).
These origins provide a diversity of production situations on a
large scale that has no parallel in any other crop grown in the U.S.
and research opportunities that allows investigation of pecan
arthropods from their natural state to intensively managed production
agriculture conditions with all manner of intermediate situations
available for study as well. Investigation of the complex and dynamic
nature of the arthropod/pecan interaction and its impact on
production agriculture benefits from this diversity because field
situations can be found to actually test hypotheses in pecan whereas
only speculation and computer simulation would be possible in most
other crops.
The diversity of pecans available today is, however, much less
than that at the turn of the century. Native pecans and seedling
orchards are not to any appreciable extent being replaced as they
die. Slowly but surely the base for commercial production is being
shouldered by the "best" of the vegetatively propagated cultivars and
this uniformity provides greater opportunities for pests previously
kept off-balance in environments where every tree was genetically
distinct. The effects of this increasing uniformity were recognized
60 years or more ago as pecan scab became more severe and 20 years or
so ago as pecan twig phylloxera was observed to preferentially attack
specific cultivars. Resistance "breaks down" is the common
observation, but in reality the virulence of the pest "catches up"
with the now genetically frozen pecan planted in monoculture. Wheat
and other annual crop farmers can deal with this kind of problem by
switching varieties (Harris 1980). That solution is of limited value
with current pecan technology, and increased narrowing of the germ
plasm means similar problems will occur in the future.
The trend towards having more and more of our production dependant
upon a narrower and narrower genetic base is a potential time bomb in
a production system with a useful life of 100-200 years. A narrowed
genetic base unquestionably reduces the ability of the pecan to
defend itself against arthropod and pathogen attack and artificial
defenses using chemicals, sanitation, etc., are needed to maintain
productivity (Harris 1980, 1983, 1988). If diversity can save one
treatment at $60/hectare each year and those profits were invested at
6% annually, the compounded return would be $338 thousand after 100
years and $114 million after 200 years. The analogy is admittedly
unrealistic because of the unknowns of inflation, taxes, acts of God,
war, etc., but is this less visionary than planting a new orchard to
the "best" cultivar and one or two pollinators and expecting current
budget figures to apply over the same time frame? History shows the
narrower genetic base becomes increasingly plagued with pest problems
requiring more and more overt management to maintain the same level
of production so that today's advantages are often rapidly lost. The
inability to rapidly and economically switch cultivars should cause
us to ask how much diversity is needed to prevent or delay the need
for overt management?
Varietal selection and breeding programs serve as the predominant
source of new cultivars. These efforts emphasized precocity,
productivity, and marketability of specific selections based on
limited evaluations over short time spans compared to the century
plus life of orchards planted to them. This is analogous to a
football team composed exclusively of wide receivers that can
surprise the opposition for a while but ultimately suffers from a
lack of balance. Rectifying this weakness will require modifying our
selection requirements from the individual archetype to the
population archetype that allows improvement while maintaining
diversity.
PECAN MANAGEMENT
Current management practices vary from treating the pecan as a
gift of nature and harvesting the trees when they produce a crop to
state-of-the-art systems of high density, carefully selected and
pruned cultivars that are irrigated, fertilized and protected with
the latest pesticides, and mechanically harvested, shelled and
refrigerated in storage until being sold. The gift of nature grower
harvests a crop every 2-5 years while the intensive manager expects a
crop every year. No single system of arthropod management is
compatible with this diversity of production situations. Careful
examination of each production situation is needed and an arthropod
management plan should be developed that is consistent with the
overall production program (Harris 1983, 1985).
Earlier I noted the diversity of geographic areas from the arid
climate and basic soils of the west to the humid climate and acid
soils of the southeast where pecans are grown. These factors too can
affect the options available in pecan arthropod management,
particularly in regard to pesticide application using a spray
machine, typically an air blast sprayer. Their primary uses are for
application of zinc for prevention of rosette, fungicides for disease
management, and acaricides and insecticides for arthropod management;
and, tank mixes of all three amendments can be used simultaneously to
"solve" rosette, disease and arthropod problems in a single
application reducing wear and tear costs on equipment and a labor and
water savings of up to 66% compared to separate applications. This
makes excellent economic sense when all applications are really
needed but can result in unnecessary costs or even disasters when one
or more of the treatments are not needed. Tank mixing unneeded
insecticides or miticides with needed zinc or disease treatments is
the greatest single threat to a sound arthropod management program
faced by the pecan industry.
PECAN ARTHROPOD MANAGEMENT
The central consideration to a sound pecan arthropod management
program is to only undertake a management action if one or more
target pests are present in sufficient numbers to seriously threaten
to cause economic damage and the action taken will significantly
reduce or remove that threat. Following this guideline requires
an ability: 1) to identify the pests, 2) to assess population levels,
3) to relate pest density to economic damage, and 4) to be able to
take effective management action. Most arthropod research and
extension efforts are directly related to these four aspects of pest
management.
Fig. 1 shows how the major pests in the pecan arthropod complex
relates to rosette, pecan scab and other diseases. This overview
illustrates that pest problems responsive to management occur from
before budbreak until leaf drop, a period of about 250 days.
Fortunately, the problems at a particular location can usually be
reduced to a subset of the general profile in Fig. 1 for many
reasons. Pests differ in their distribution and intensity from
location to location due to geographical barriers and climate. For
example, pecan weevils do not occur west of the native range, or in
Mexico, or in localized regions from Texas to Georgia, and thus pose
no immediate threat to pecan production at these locations. Pecan
scab is most intense where significant rainfall and high humidity
coincide with rapidly growing pecan leaves and nuts and pathogen
sporulation. Thus, pecan scab is of virtually no consequence in the
arid west but increases in intensity as one moves east. Rosette is
especially severe where pecans growing in basic soils cannot access
Zn because it is tied up in such soils. Thus, rosette tends to be
most severe in the limestone soils of the west and diminish in
severity as soils to the east become more acidic; however, the
practice of liming acidic soils to increase N uptake can also tie up
Zn so that foliar Zn amendments are needed there for optimum
production as well. In short, effective pecan arthropod management
demands a thorough understanding of the overall context of pecan
production at the specific location, as well as an understanding of
the pecan arthropod complex. Extensive literature is available
outlining these approaches and resulting programs (see Boethel and
Eikenbary 1979; McVay and Ellis 1979; Peeples and Brook 1979; Harris
1983, 1985; Cooper et al. 1982, etc.).
The details of current IPM programs are a result of innumerable
large and small changes that continuously occur to maintain
profitability of pecan production. This evolution is so much a part
of the fabric of production that one must deliberately reflect upon
how and why we conduct them in their present form and to anticipate
how future problems may be resolved.
The wild pecan produces large crops at irregular intervals and
primarily defends itself against the key nut feeders, pecan nut
casebearer and pecan weevil, by cycles of starvation and satiation
(Harris et al. 1986; Harris 1988). Foliage feeding arthropods rarely
remove more than 10% of the leaves during a season (Ring et al. 1985)
and severe infestations appear to either be limited to outbreaks on
single trees or widespread epidemics that affect all trees more or
less equally (Harris 1980). Phylloxera devastatrix is an
example of the former and Datana integerrima the latter. Note
that neither type of severe foliar infestation interferes with cycles
of irregular bearing in wild trees. D. integerrima delays the
bearing year and P. devastatrix has virtually no effect since
few trees are affected. Apparently, severe pathogen infestations are
also primarily limited to single wild trees with similar effect.
The rapid adoption of vegetative reproduction a century ago has
resulted in planted orchards where most trees are genetically
identical contrasted to wild populations where every tree is
genetically distinct. Pruning, fertilization, and irrigation in
combination with selection of cultivars with a propensity to bear
regular crops ensures nut production every year.
The pecan nut casebearer has been a key pest of pecan throughout
the pecan-producing states east of the Pecos causing damage almost
every year from at least the early 1900s until the advent of new
chemicals and application equipment following WWII. Although it
remained a key pest up to the present in most areas west of central
Louisiana, reference to damaging populations in the southeastern U.S.
virtually disappears after the advent of mechanized chemical
agriculture. I believe these differences came about because of the
different driving forces at work in these diverse geographical and
climatological areas.
Pecan nut casebearer (PNC) was the most important pecan pest in
Texas in the late spring at the advent of the post WWII period and
even though rosette and pecan scab were also problems, addressing
them made little sense to southwestern growers routinely devastated
by PNC. B. Hancock (Pecan Horticulturist, Extension, Texas A&M
Univ., 1952-present, pers. comm.) recalls how programs to manage PNC
were the impetus to also tank mix with zinc sulfate for rosette and
later fungicides for pecan scab control in the mid 1950s beginning in
the Guadalupe River Valley. Successful PNC control in the southwest
became the cornerstone for all other management programs mediated by
the new chemical application equipment and chemicals that made it
possible.
Southeastern growers, in contrast, were plagued with pecan scab.
This pernicious disease thrives best in hot, humid environments on
rapidly growing tender pecan leaves from April to June and nutlets
from May to August. The massive expanses of 30-50 year old
vegetatively propagated pecans with often overlapping canopies and an
excess of 30 inches of rainfall from April to September provided
ideal epidemic conditions virtually every year that especially
frustrated the more progressive growers because most practices that
increased yield, like fertilization or zinc amendments, also
stimulated and prolonged growth of tender tissue that would be
infected with pecan scab. Nuts could only be destroyed once and pecan
scab masked other mortality forces by a wide margin. The same
breakthroughs in chemistry that produced post WWII insecticides for
the southwest for PNC brought fungicides to the southeast for pecan
scab (Table 1).
The time window of vulnerability to first summer generation PNC
for a given orchard is about 3 weeks during the late April to early
June period depending on the exact location of the orchard. Growers
in the southwest could provide prophylactic coverage with two
insecticide treatments during this period and achieve excellent PNC
control. The primary extension scientists working with pecan
immediately after WWII were horticulturists and recommending this
schedule in the late spring in the southwest also ensured that two
zinc treatments for rosette could be applied at little additional
cost with a marked benefit in tree vigor.
The time window of vulnerability of pecan scab is dependent upon
having a virulent pathogen, a susceptible host and a favorable
environment. Southwestern growers in the native range were buffered
from pecan scab by a preponderance of genetically diverse trees that
prevented pathogen specialization and a more arid climate that
produced fewer rains to constitute infection periods. Often,
fungicides applied with PNC and zinc treatments prevented disease
establishment in the early season and an unfavorable environment
combined with a low inoculum provided sufficient protection for the
remainder. Producers in the southeast faced a much tougher challenge
from pecan scab (Cole 1941). Vegetatively propagated trees severely
limited the genetic diversity and allowed the pathogen to specialize
on the limited varieties, and heavier and more frequent rainfall
significantly extended the window of vulnerability. Enterprising
growers began to spray fungicides every 2 to 3 weeks during April to
September for scab control and also piggy-backed zinc and other
pesticide treatments into this schedule when other pest problems
became more evident in the absence of pecan scab (Miller et al.
1982).
Thus, the initial patterns for pecan arthropod management in the
two major pecan production regions were established for the post WWII
era. Results were dramatic in each region with the heaviest pesticide
use occurring in the southeast where the window of vulnerability to
pecan scab was so long. The ability to effectively manage PNC in the
southwest and pecan scab in the southeast allowed producers to detect
other problems that were not as obvious before like rosette,
fertilization, and pecan weevil. Pecan weevil became a problem across
the entire pecan belt because improved pecan management resulted in
healthier more productive trees that produced large crops of sound
pecans on a regular basis (Harris et al. 1980). This provided
unlimited food for pecan weevil and insect populations soared. The
initial answer to this problem was another chemical and today, 2-3
applications of carbaryl at 10-14 day intervals beginning in late
August are used for control from West Texas to the Atlantic Coast
wherever pecan weevil occurs.
The advent of effective chemical agriculture in pecan occurred
later than in many other areas like cotton, corn, dairying and apple.
This was primarily due to the lack of effective equipment to move
chemicals into the tops of trees 20-30 meters above the ground. The
pecan industry inherited chemicals from other agricultural sectors
virtually as soon as they were developed, but the first practical and
effective machines were airblast sprayers modified from the fruit
industry in the 1950s and early 1960s. This only explains in part how
the pecan industry escaped the drawbacks of chemical agriculture much
longer than other agricultural sectors; namely, arthropods resistant
to pesticides, outbreaks of secondary pests, and pollution. The pecan
industry is unique in that the first pest reported to be resistant to
a pesticide was a fungal pathogen rather than an arthropod. Pecan
scab resistant to benomyl was reported in 1975 in Georgia followed by
hickory scorch mite to some carbamates and organophosphates in 1979
in Louisiana (see Harris 1983). Dutcher and Htay (1985) reported
pecan aphid resistance to pyrethroids in 1985, many decades after
reports on similar arthropods on comparable crops had manifested
themselves. Interestingly, however, pyrethroid resistance appeared
only a few years after this new class of chemical became available
for use on pecan and this is a quite respectable interval if we were
competing in a race for obtaining resistance.
Arthropod resistance to pesticides in pecan is primarily due to a
drastic reduction of genetic diversity of pecan through vegetative
propagation that predisposes orchards to increasing problems from
pecan scab. This necessitates increased fungicide treatments at
shorter intervals using machinery that provides thorough coverage of
the foliage. A general intolerance of pest arthropods and a plethora
of initially effective insecticides makes them appear "cheap" to add
to the tank mix from a short-term perspective.
The cycle of subsistence, exploitation, crisis, disaster and
integrated control Dutcher (1981) foresaw as also applying to the
pecan industry culminated in 1985 when the Federated Pecan Growers
declared the pecan aphids (secondary pests) the most important pest
problem facing producers and said in essence that if the disaster was
not resolved, the industry itself was in jeopardy. The southwest
participated in this disaster as well, piggybacking insecticide on
needed zinc and occasional fungicide treatments to the extent that
one grower in the Mesilla Valley spent more than $500,000 in one year
for aphid control without success. Whereas the disasters of a
generation earlier in cotton, corn, apples, etc. (Bottrell 1979), and
the formal IPM programs in pecan begun in 1977 (Harris 1985), were
insufficient "teachable moments" to move from exploitation to
integrated control, thereby skipping the crisis and disaster phases
of the cycle, the pecan aphid complex proved to be the vehicle of
change that brought many producers to IPM. Mark Twain observed that
some matters defy description and must be personally experienced to
be appreciated, and gave as his example "carrying a cat home by the
tail". Perhaps, despite my earlier optimism (Harris 1983), a
catastrophe must also precede adoption of IPM in each commodity.
The disaster phase of the cycle is not over even though much
progress has been made in re-establishing reliance on natural enemies
for aphid control in most situations. A major root of the problem is
still the genetically frozen pecan that allows genetically flexible
pests to fine tune their genetic capacities to exploit these massive
expanses of fixed hosts so that management becomes increasingly
difficult. Novel chemistry and improved equipment have, along with
other technologies, kept pace with this evolution. The trend is
toward less chemical development and continued reductions in the
existing arsenal due both to resistance and for economic reasons, as
the loss of phosalone exemplifies. Public concerns with pollution,
worker safety and a wholesome food supply also indicate that reliance
on chemical agriculture will diminish in the future.
Table 1.
An abbreviated history of pecan and factors affecting arthropod
management
Prior to 1800 - Native Americans gathered and
subsisted on pecans in their season and early explorers and settlers
readily adopted them to their diets.
1800 to 1900 - Settlers thinned tree stands in
native range leaving pecans and grass for grazing. Seedling orchards
established in the southeastern U.S., particularly near the turn of
the century. Grafting technology for pecan developed but not heavily
implemented until the last decade (Stuckey 1941). Rail transportation
results in shipment of nuts to urban markets.
1900 to 1930 - Vegetative reproduction inundates
southeastern U.S. with many selected varieties. Land development
schemes sold small acreage of subdivided orchards (Littlepage 1913).
Bordeaux spray 3-10 times recommended for nursery trees to prevent
scab but large orchard trees considered unreachable; also plant
resistant trees like Stuart, Schley and Frotscher (Waite 1914). Early
harvest, sanitation, burning and Persian insect powder used for
insect control (Morris 1912; Quaintance 1914).
1930 to 1940 - Shelling machinery, transportation
and consolidations of orchards into economic units increase
marketability of pecans. Expanded production of the most popular
varieties like Stuart is met with increasing levels of pecan scab on
previously resistant varieties (Stuckey 1941). Rosette linked to
foliar zinc deficiency and lead arsenate and nicotine sulfate
recommended for insect control (Rainey 1960). Spray machinery
expensive, labor intensive and rarely employed (Milward 1940).
1940 to 1950 - Tank mixing of nicotine sulfate with
needed fungicides recommended as "cheap insurance" (Moznette 1941 a
and b). Contract spray services expand with truck-mounted hydraulic
sprayers (Milward 1940, Anon. 1941). DDT used for pecan nut
casebearer but aphids and mites appeared in epidemic numbers;
toxaphene alone or mixed with nicotine sulfate controlled pecan nut
casebearer without resurgence of aphids and mites (Rainey 1960).
1950 to 1960 - Airblast speed sprayers become
generally available; compared to hydraulic sprayers (Brison 1960),
the cheaper speed sprayers allow a single operator to spray the same
number of trees with one-fourth the water and still obtain better
coverage (Shelton 1960). Effective and economical rosette, arthropod
and pathogen control with conventional and newer chemicals resulted.
Malathion was adopted for pecan nut casebearer control (Rainey 1960).
Chemical management of pecans became widespread.
1960 to 1970 - Cyprex and then Du-Ter replaced
Bordeaux for pecan scab control and new carbamates, organophosphates
and systemics became available for arthropod control (Denman 1965;
Denman and Hancock 1965; Littrell 1983). Mechanization for pesticide
application, pecan maintenance, harvesting and processing burgeoned
along with the explosion of chemicals and solutions appeared faster
than problems. Chemical schedules became routine and screening for
efficacy dominated research efforts.
1970 to 1980 - Carbaryl became chemical standard for
pecan weevil management, phosalone for other arthropods, Benlate and
Du-Ter for pathogens, and NZN or zinc sulphate + uran for rosette.
The first case of pesticide resistance in pecan was a pathogen, the
causal agent for pecan scab, to Benlate in 1975, followed by an
arthropod, hickory scorch mite, resistance to carbamates and
organophosphates in 1979. Synthetic pyrethroids, a new class of
chemicals for arthropod control, introduced late in the decade.
Integrated Pest Management (IPM) philosophy develops and spreads
across agriculture due to widespread pesticide resistance by
arthropods, secondary pest outbreaks like aphids, mites and
leafminers due to broad spectrum pesticides killing natural enemies
and societal concerns about environmental pollution. Pecan industry
as a whole was buffered from many of these problems because of the
surfeit of chemicals for all pests (Dutcher and Payne 1982) and
lagging problems of resistance due to remaining management diversity.
However, aphids were viewed as a major problem in the El Paso Valley
of Texas and increased reliance on natural control by predators and
parasites resolved this problem there. Increased attention in pecan
was paid to developing economic thresholds of important pests,
refining understandings of basic biologies to predict and manage
pests, to identify and rely on natural enemies of pests and other IPM
strategies. Pecan IPM programs initiated in Alabama, Georgia, Texas
and elsewhere late in the decade. Widespread expansion of new pecan
plantings of a few varieties occurred in the Southwest and Mexico
inside and outside the native range epitomizing the drastic narrowing
of genetic diversity in the natural pecan population compared to the
cultivated varieties.
1980 to 1990 - Arthropod resistance to pesticides
becomes widespread and Federated Pecan Growers (Beshears 1988)
declare aphids the most destructive pest in 1985, refuting the
contention by Harris (1983) that the pecan industry had adopted IPM
without the normal cycle of subsistence, exploitation, crisis,
disaster and finally integrated control (Smith 1969, as quoted by
Dutcher 1981). Modeling efforts and basic biological studies on pecan
nut casebearer, pecan weevil, hickory shuckworm, pecan aphids, pecan
scab and other pests began to be implemented into management programs
(Harris 1983; Hudson 1983). Phosalone was withdrawn from the market
in 1989 due to the producing companies unwillingness to risk costs of
federal re-registration requirements against potential revenue or
perhaps refusal of registering the chemical. Implications of the
continued transition from the diverse native and seedling trees to
increased genetic uniformity of vegetatively propagated varieties on
the ability to manage diseases and arthropods became ever more
apparent, continuing a trend observed at least half a century
earlier.
REFERENCES
Anon. 1941. Cover photograph. The Pecan Journal 1: 8.
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States. South. Pecan Grow. Assoc. Proc. 21 pp.
Boethel, D.J., and R.D. Eikenbary. 1979. Status of pest management
programs for the pecan weevil. In Pest Management Programs
for Deciduous Tree Fruits and Nuts (D.J. Boethel, R.D. Eikenbary,
ed.). pp. 81-119. New York: Plenum. 256 pp.
Bottrell, D.R. 1979. Integrated Pest Management. Counc.
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Brison, F.R. 1960. Experience in the control of pecan nut
casebearer with a hydraulic sprayer. Proc. Tex. Pec. Grow.
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Brison, F.R. 1974. Pecan Culture. Capitol Pres. Austin,
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