A g r i c u l t u r a l I n n ov a t i o n s Fact Sheet
B i o l o g i c a l C o n t r o l o f P \f c a n W \f \f v i l s i n t h \f
S o u t h \f a s t \b A S u s t a i n a b l \f A p p r o a c h
William G. Hudson 1,2, David \f. Shapi\bo-\fl\van 3, Wayne A. Ga\bdne\b 4, Ted E. Cott\bell 3, Bob Behle 5
Inside this fact sh\Weet:
• Introduction
• Pecan Wee\fil Life C\bcle and\W Impacts
on Crops
• Fungal Pathogens for Pecan Wee\fil
Suppression
• Using Fungal Pathogens to Control\W
Pecan Wee\fils
• Economic Consider\Wations of Trunk
Applications
• Other Ad\fantages \Wof Trunk Applicat ions
• SARE Research S\bnopsis
• References
SARE Agricultural Innovations are based on
knowledge gained f\Wrom SARE-funded projects.\W
Written for farmers\W, ranchers, and ag\Wricultural
educators, these p\Weer-re\fiewed fact s\Wheets pro -
\fide practical, han\Wds-on information \Wto integrate
well-researched su\Wstainable strategies into farm -
ing and ranching s\W\bstems. The articles are written\W
b\b project coordina\Wtors and published\W b\b SARE.
Geographic Applicabili\Wt\b:
The techniques disc\Wussed here are app\Wlicable to pe -
cans grown in areas of t\Whe southeastern U.\WS. where
pecan wee\fil is a k\We\b pest.
I n t r o d u c t i o n
P
ecan ( Carya illinoensis ) is the most valuable nut crop
native to North America. There are more than 492,000
acres of managed pecans in the United States, with major
production in the Southeast, Southwest and parts of the
Midwest. Total annual value of the crop to U.S. growers
generally exceeds $300 million.
Insects and mites can cause severe crop losses in pecans.
Of major concern is the pecan weevil, Curculio caryae (Fig.
1). This weevil attacks the pecan nut in late season, causing
serious crop losses in many areas of the Southeast, Texas
and Oklahoma. It is considered a key pecan pest, as damag -
ing populations occur year after year. Without insecticide
treatments, crop losses can exceed 75 percent.
Our research goal was to provide an alternative control
strategy for pecan growers who, for a variety of reasons,
find conventional spraying of insecticides unsuitable. This
includes organic growers, and owners of dooryard trees,
small orchards and commercial orchards who have con -
cerns regarding spray drift. We attempted to sort and iden -
tify naturally occurring fungal strains that were effective at
killing pecan weevils and provided improved fungal persis -
tence in the orchard, thus extending the effective period of
control. We also sought to develop an efficient and practi -
cal method of applying the fungal formulations in pecan
PDF a\failable at www\W.sare.org/publicat\Wions/factsheet/pdf\W/0910.pdf
Photo by Peggy G\beb, cou\btesy ARS, USDA
1) Depa\btment of Entomology, Unive\bsity of Geo\v\bgia, P.O. Box 748,
Tifton, GA 31793
2) Co\b\besponding au\vtho\b, e-mail wghudson@u\vga.edu
3) USDA-ARS, Southeaste\bn F\buit and T\bee Nut Resea\bch Lab\vo\bato\by,
By\bon, GA
4) Depa\btment of Entomology, Unive\bsity of Geo\v\bgia, G\biffin Campus,\v
G\biffin, GA
5) USDA-ARS, National Cente\b \vfo\b Ag\bicultu\bal Utilizat\vion Resea\bch,
Peo\bia, \fL
B i o l o g i c a l C o n t \b o l o f P e c a n W e e v i l s i n t h e S o u t h e a s t w w w . s a r e . o r g 2
orchards. This fact sheet provides information about the life
cycle of the pecan weevil and its impacts on pecan crops;
identifies fungal pathogens that can control pecan weevils;
and outlines methods for application of these fungal patho -
gens in orchards.
P \f c a n W \f \f v i l L i f \f C y c l \f a n d
I m p a c t s o n C r o p s
Throughout most of the southeastern United States, adult
weevils emerge from the soil over a period of about six
weeks beginning in late July, with peak emergence in
early- to mid-August. In Texas and Oklahoma, emergence
is somewhat later. The weevils crawl or fly up into the trees
and feed on immature nuts. Once the nuts reach the stage
where the shells begin to harden, female weevils chew holes
in the shuck and through the shell, and deposit their eggs.
Larvae feed on the developing kernels until they reach ma -
turity and drop to the ground. They dig down 4-12 inches
in the soil and construct a pupal cell where they remain
for 2-3 years before emerging as adults. Nuts damaged by
early-season feeding usually fall prematurely, while those
damaged after shell hardening remain on the tree until
harvest or natural drop occurs.
Direct pecan damage results from adult feeding prior to and
after shell hardening, and by grub feeding in the partially
mature kernel after shell hardening. Indirect damage is
caused by the insecticides used to control the weevils be -
cause these materials—carbaryl and a variety of pyrethroid
insecticides—tend to encourage outbreaks of pecan aphids
and pecan leaf scorch mites. These secondary pests have the
potential to cause significant leaf damage and even pre -
mature defoliation. While both can be reduced effectively
with available insecticides, controlling these late-season
outbreaks will add significantly to both production costs
and the amount of pesticide introduced into the orchard
environment.
Identifying new and sustainable pecan weevil management
methods is vital to the industry for these reasons, and also
because the carbamate and pyrethroid classes of insec -
ticides are older chemicals scheduled for re-registration
review and are likely, in the near future, to have more
stringent restrictions placed on their use in pecan orchards.
Growers need new approaches and materials that will pro -
vide acceptable control of weevils without the environmen -
tal and non-target effects of the insecticides currently used.
F u n g a l P a t h o g \f n s f o r P \f c a n
W \f \f v i l S u p p r \f s s i o n
A highly promising management alternative for pecan wee -
vils is the use of fungal pathogens from the entomopatho -
genic Hypocreales fungus group, particularly Beauvaria
bassiana and Metarhizium anisopliae . These are among
the best known and most studied insect pathogens, and
specific strains of both species are commercially produced
for pest control in many crops worldwide. Native strains
of these fungi occur naturally in the soil of pecan orchards,
where they attack and kill a variety of insects in both the
adult and immature stages. The different strains can vary
widely in virulence to different target insects. Earlier work
has shown that the commercial strain of B. bassiana , par -
ticularly, has potential for controlling adult pecan weevils. 1, 2
In laboratory experiments, we screened several strains of
both Beauveria bassiana and Metarhizium anisopliae for
virulence against pecan weevil adults and for persistence in
soil. Two promising strains were selected for further study
under field conditions: Beauveria bassiana GHA strain and
Metarhizium anisopliae F52 strain. Additionally, labora -
tory experiments were conducted to determine the effect
of soil amendments (e.g., compost, manure, etc.) on fungal
Fig. 1. Healthy pec\van weevil on pecan \vnut.
Fig. 2. Pecan t\bee with fibe\v\b band t\beated with \vfungus.
B i o l o g i c a l C o n t \b o l o f P e c a n W e e v i l s i n t h e S o u t h e a s t w w w . s a r e . o r g 3
persistence and virulence. Composted peanut hulls were
most promising and chosen for further testing in the field.
We conducted field studies using B. bassiana and M. aniso -
pliae over three growing seasons.
We tested a variety of application approaches under field
conditions:
1) bare ground applications
2) a cloth band treated with the fungus stapled to the tree
(Fig. 2)
3) ground application with a cover crop (Sudan grass)
4) ground application with cultivation
5) application directly to the trunk
6) trunk application with a UV-protecting adjuvant and a
combination of ground and tree band application.
Following treatment, naturally occurring weevils were
trapped as they climbed into test trees and assessed for
fungal infection. All studies were conducted in an orchard
at the U.S. Department of Agriculture Agricultural Research
Service station at Byron, Ga., except in the last season
(2006), when three commercial pecan orchards were added
(two in Georgia and one in Texas).
The most successful treatment was spraying B. bassiana
directly to the trunk, resulting in a rate of more than 75
percent mortality of weevils (Fig. 3a)—comparable to trunk
application with the insecticide carbaryl. Adding a UV pro -
tectant did not improve results.
Grower trials with B. bassiana trunk sprays in Georgia were
also very successful: 90-100 percent mortality occurred
in weevils collected from two commercial orchards. Band
application of M. anisopliae was tested at a single Georgia
location, but did not provide significant control. Trials in
Texas were inconclusive, possibly due to low weevil popula -
tions.
U s i n g F u n g a l P a t h o g \f n s t o
M a n a g \f P \f c a n W \f \f v i l s
Trunk Applications
Trunk applications of any insecticide are better than ground
applications for controlling weevils. Application to the
trunk is straightforward. Virtually any type of sprayer can
be used, from pump-up garden sprayers to commercial
orchard sprayers with handgun attachments. The product
should be mixed in water according to label directions (for -
mulations vary, but mix at the strength recommended for
a spray application) and applied to the trunk in a band 3-5
feet wide, all the way around the tree. It is important to wet
the bark thoroughly so any weevils crawling up the tree will
contact the fungal spores.
Timing of application depends on weevil emergence pat -
terns. These depend on weather and other factors, but a
good rule of thumb is to plan an application in the first
week of August with a second application 2-3 weeks later.
For help with precise timing for your area, contact your lo -
cal Cooperative Extension office.
Fiber Band Applications
We also found that treating a fiber band with M. anisopliae
and stapling the band around the trunk produced higher
mortality than ground application of fungal pathogens (Fig.
Fig. 3a. Weevil cadave\b infect\ved with Beauveria bassiana\l .
Fig. 3b. Weevil cadave\b infect\ved with Metarhizium anisop\lliae .
B i o l o g i c a l C o n t \b o l o f P e c a n W e e v i l s i n t h e S o u t h e a s t w w w . s a r e . o r g 4
3b). Any porous absorbent material can be used for the
trunk band, as long as it will soak up the fungal solution
and wrap around the tree. Burlap has traditionally been
used for this purpose, but synthetic fabrics are also effec -
tive. We used a woven fiber material that was impregnated
with the fungus by the fungus producer, Novozymes Bio -
logicals of Salem, Va. 3 The bands are not yet available com -
mercially but can be ordered from the producer. They can
be secured to the tree with staples, rope, cord, strapping or
any other method. Place the band anywhere on the trunk
below the first scaffold limbs so that weevils crawling up the
trunk will contact the fungus. If there are pets or other live -
stock in the area, it is probably best to attach it high enough
that the animals will not be tempted to chew or pull it from
the tree. Bands should be placed on trees in early August
in most years. For more information about implementing
these techniques and assistance with precise timing for
your area, contact your local Cooperative Extension office.
There are a number of producers of fungal materials con -
taining B. bassiana and M. anisopliae worldwide, but only
a few have products registered in the United States. Two
producers of Beauveria products are Laverlam-Internation -
al Corp. of Butte, Mont., (Botanigard®) and Troy Biosci -
ences of Phoenix, Ariz. (Naturalis®: note that this product
contains a different strain of B. bassiana than the one we
tested and may not perform in the same ways). 4,5 Metarhi -
zium anisopliae is produced in the United States by Novo -
zymes Biologicals of Salem, Va. These products are sold by
many garden centers in larger markets and through Inter -
net suppliers of biological control products worldwide.
E c o n o m i c C o n s i d \f r a t i o n s o f
Tr u n k A p p l i c a t i o n s
In addition to providing environmentally benign control
of a serious pecan pest, trunk applications allow a grower
to treat effectively without the expense of an air-blast
sprayer, and to apply material only to the trees, reducing
the problem of off-target drift of spray solution common
with standard orchard sprayers. Air-blast sprayers typi -
cally cost $50,000 or more, making the purchase difficult to
justify for growers with smaller orchards. Contract spraying
may be employed, but this also adds cost to production of
the crop. Additionally, sprayers employ powerful fans that
propel the spray up into the canopy in a fine mist which can
cause the applied materials to drift onto nearby property.
Near residential areas, growers typically leave several rows
unsprayed as a buffer to avoid conflict with neighbors, often
allowing weevil damage to occur in these outside rows.
The increase in time and hand labor required to apply the
fungal materials to individual trunks throughout an orchard
should be economically offset by reduction in border rows
damage.
Growers with small orchards, organic producers and
homeowners are likely to be the first adopters of fungal
applications, as the added expense of trunk application will
initially deter most commercial producers from adopting
this technique. However, any changes in availability of the
standard insecticides currently used for weevil control will
almost certainly make fungal pathogens more competitive
in cost. With efficacy comparable to most chemical insec -
ticides and without the tendency to induce secondary pest
outbreaks, the fungal alternative should be attractive to
larger-scale growers as well. Leaving orchards untreated is
simply not an option for a commercial operation.
O t h \f r A d v a n t a g \f s o f Tr u n k
A p p l i c a t i o n s
For small-scale pecan producers—those with only a few
trees, often around a home—whole-tree spraying is not eco -
nomically feasible, and raises the additional concern of pes -
ticide exposure for homeowners, children and pets. Trunk
application of fungal pathogens provides an effective weevil
control alternative that has the benefit of being essentially
non-toxic to everything except insects. The combination of
safety and efficacy will be very attractive for people with a
few pecan trees near their homes.
Organic pecan production is rising and these farmers have
shown the most interest in using the fungus for weevil
control. We anticipate the fungus applications will be in -
corporated as part of sustainable Integrated Pest Manage -
ment (IPM) programs in orchards where other biocontrol
methods are being used (such as releasing predatory mites
for scorch mite control, using fungi to control aphids or
complementing fungus applications for weevil control with
beneficial nematodes). Additional research should include
studies of the efficacy on crop damage of the weevil control
methods presented here.
S A R E R \f s \f a r c h S y n o p s i s
In laboratory experiments, multiple strains of two patho -
genic fungus species ( B. bassiana and Metarhizium an -
isopliae ) were screened for virulence and persistence. Two
promising strains of fungi were the subject of additional
studies under field conditions: Beauveria bassiana GHA
strain, and Metarhizium anisopliae F52 strain. Addition -
ally, experiments were conducted to determine the effect
B i o l o g i c a l C o n t \b o l o f P e c a n W e e v i l s i n t h e S o u t h e a s t w w w . s a r e . o r g 5
of soil amendments (e.g., compost, manure, etc.) on fungal
persistence and virulence. The amendment deemed most
promising (composted peanut hulls) was tested further in
field experiments.
A variety of application approaches were tested under field
conditions in pecan orchards from 2004 to 2006.
For B. bassiana GHA strain, treatments included:
(1) application to bare ground;
(2) ground application with a cover crop (Sudan grass);
(3) ground application with cultivation;
(4) application directly to the trunk; and
(5) trunk application with a UV-protecting adjuvant.
For M. anisopliae , trial treatments included:
(1) a cloth band containing the fungus stapled onto the
tree trunk;
(2) a ground application; and
(3) a combined ground application and tree band.
All experiments also contained a non-treated control. The
compost amendment was tested in 2006. All experiments
were conducted on the USDA-ARS research station in
Byron, Ga., except in 2006 when three commercial pecan
grower fields were also included (two in Georgia and one in
Texas).
In field experiments focusing on B. bassiana GHA strain
in 2005 and 2006, experiments in Georgia indicated that
all fungal treatments showed significant weevil mortality
relative to the control. Weevil mortality reached 80 per -
cent during 10-14 day periods. In 2006, when analyzed by
sample date, some evidence indicated trunk applications
were superior to ground applications. In field experiments
focusing on M. anisopliae application, 2006 results indi -
cated the trunk band method caused significantly greater
weevil mortality than the control, whereas direct ground
application with or without compost amendment failed to
cause a significant effect. Results in 2005 also indicated a
significant effect of the band application approach, but only
at 15-day post-application.
In grower trials (2006), the trunk application approach
with B. bassiana caused 90-100 percent mortality (in two
Georgia locations), yet the M. anisopliae treatment did not
provide significant control (tested in one location). The
grower trial in Texas showed variable effects of the fun -
gus, possibly due to low weevil counts. Overall, the results
indicate that using fungus as a biological control measure
for pecan weevil management is promising, particularly the
trunk-spray approach. The cover crop and the trunk band
(cloth impregnated with fungus) control methods also ap -
pear to have potential.
R \f f \f r \f n c \f s
1. Shapiro-Ilan, D. I., T. Cottrell, and W. A. Gardner. 2004.
Trunk perimeter applications of Beauveria bassiana to sup -
press adult Curculio caryae (Coleoptera: Curculionidae). J.
Ent. Sci. 39: 337-349.
2. Shapiro-Ilan, D. I., W. A. Gardner, T. E. Cottrell, R. W.
Behle, and B. W. Wood. 2008. A comparison of applica -
tion methods for suppressing the pecan weevil (Coleoptera:
Curculionidae) with Beauveria bassiana under field condi -
tions. Env. Ent. 37: 162-171.
3. Novozymes Biologicals, www.bioag.novozymes.com .
4. Bioworks, Inc., “Where to Buy”, Botanigard ®; http://
www.bioworksinc.com/dist.html.
5. Troy Biosciences, http://www.troybiosciences.com/
products.asp .
A c k n o w l \f d g m \f n t
Bruce Wood, USDA/ARS Byron, GA, Marvin Harris, Texas
A&M Univ. College Station, and Bill Ree, Texas A&M Bry -
an provided invaluable input and assistance in the course
of the research.
S A R E P u b l i c a t i o n # 0 9 A G \f 2 0 1 0
This fact sheet is \Wbased on a
SARE-funded project. \WFor more informa -
tion, please \fisit \Wwww.sare.org > Projec\Wt
Reports > ‘Search the d\Watabase’
for project # LS03-\W153.
T h i s p u b l i c a t i o n w a s d e v e l o p e d b y t h e \f u s t a i n a b l e A g r i c u l \b
t u r e R e s e a r c h a n d E d u c a t i o n ( \f A R E ) p r o g r a m w i t h f u n d i n g
f r o m N a t i o n a l I n s t i t u t e o f F o o d a n d A g r i c u l t u r e , U \f D A . A n y
o p i n i o n s , f i n d i n g s , c o n c l u s i o n s o r r e c o m m e n d a t i o n s e x \b
p r e s s e d h e r e d o n o t n e c e s s a r i l y r e f l e c t t h e v i e w o f t h e U . \f .
D e p a r t m e n t o f A g r i c u l t u r e .
\f A R E O u t r e a c h o p e r a t e s u n d e r c o o p e r a t i v e a g r e e m e n t s w i t h
t h e U n i v e r s i t y o f M a r y l a n d a n d t h e U n i v e r s i t y o f V e r m o n t
t o d e v e l o p a n d d i s s e m i n a t e i n f o r m a t i o n a b o u t s u s t a i n a b l e
a g r i c u l t u r e .
