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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


• Using Fungal Pathogens to Control\W

Pecan Wee\fils

• Economic Consider\Wations of Trunk


• 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


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\\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\

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


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


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 -


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


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


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, .

4. Bioworks, Inc., “Where to Buy”, Botanigard ®; http://

5. Troy Biosciences,

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 \ > 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 .


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