What is Stickiness?

To growers, stickiness means higher costsfor insect control and reduced cotton mar-ketability. To ginners, stickiness may meanspecial handling and processing require-ments. At the textile mill, stickiness meansreduced processing efficiency, lower yarnquality, and in severe cases total shutdown. For everyone concerned, stickinessmeans reduced profitability. Stickinessoccurs when excessive sugars present onfibers are transferred to equipment andinterfere with processing. Sugars may beinsect- or plant-derived. Though sugars areubiquitous in lint, they usually occur atlevels that pose no processing difficulties.This bulletin details the sources and com-ponents of problem sugars on harvestedlint, the processing and marketing impactsof stickiness, and strategies for avoidingor mitigating stickiness.

Honeydew, when present in sufficientquantity, is the main source of sugars thatcan result in sticky lint. Honeydew is ex-creted by certain phloem-feeding insectsincluding such common pests of cotton asaphids and whiteflies. These insects arecapable of transforming ingested sucroseinto over twenty different sugars in theirexcreted honeydew. The major sugars incotton insect honeydew are trehalulose,melezitose, sucrose, fructose and glucose.

Another source of stickiness is free plantsugars sometimes found in immature fi-bers. Cotton fiber is largely cellulose thatis formed from sugars synthesized by theplant. Dry, mature cotton fibers containlittle free sugar, while immature cottonfibers contain glucose, fructose, sucrose,and other sugars. If immature cotton fiberis subjected to a freeze, complex sugarsmay be broken down to release additionalsimple sugars. Less commonly, oils re-leased by crushed seed coat fragments canalso result in stickiness. In this case, raffi-nose is the characteristic sugar.

Sugars differ in their stickiness. For ex-ample, sucrose, melezitose, and trehalu-lose are all significantly stickier when de-posited on fiber than are glucose orfructose. Further, trehalulose-contami-nated fiber is stickier than fiber with anequivalent amount of melezitose. Mixturesof sugars, such as occur in honeydew, tendto be stickier than single sugars. Local-ized concentration of sugars like honey-dew is at higher risk of causing stickinessthan more evenly distributed sources likeplant sugars.

Impact of Stickiness onGrowers & the Marketplace

Between insect control costs and reducedcotton prices, sticky cotton is costly togrowers. The major cost is in controllingthe potential sources of stickiness. Thecosts of aphid control in TXand CA, and of whitefly con-trol in TX, AZ and CA haveall increased in the last de-cade. Insecticide treatment tospecifically prevent sticki-ness has cost Southwesterncotton growers $47 millionfor aphids and $154 millionfor whiteflies from 1994–98(Table 1). In AZ, the cost ofcontrolling whiteflies in-creased from $12/acre in1990 (the onset of the white-fly outbreak) to $145/acre in1995. This cost accounted for11% in 1990 and 68% in1995 of the total spent on in-sect control. A new integratedsystem of whitefly manage-ment based on insect growthregulators began in 1996.Since then, AZ growers have reduced con-trol costs to less than $35/A, while achiev-ing excellent whitefly control. The 1996AZ crop was found to be 98% free ofstickiness as determined by random baletesting with SCT (see next section). In

S U M M A R Y

From field to textile mill, all stages ofthe cotton industry are adversely af-fected by sticky cotton. Honeydew de-posited by phloem-feeding insects suchas whiteflies and aphids, and sugarsproduced by the plant itself may buildup to levels that impede fiber handling.Typically, stickiness is first encoun-tered when sugar-contaminated cottonlint is carded at the textile mill. Grow-ers often sustain considerable costs inmanaging honeydew-producing in-sects. Further, if stickiness is found bytextile processors, growers in regionsassociated with sticky cotton may suf-fer price reductions in future years. Atpresent, no test for sugars contamina-tion is as rapid as HVI testing. More-over, no current test of sugars contami-nation has been directly calibratedwith fiber processing efficiency. Be-cause current measures for mitigatingstickiness in the field and at the millare unreliable, stickiness is bestavoided by managing insect and plantsources. Well-implemented integratedpest and plant management plans areour best defenses against the stickinessproblem. Having put such plans towork, cotton growers in the westernUnited States have minimized the risksof sticky cotton.

Peter C. Ellsworth, Russell Tronstad, University of Arizona

James Leser, Texas A&M University

Peter B. Goodell, Larry D. Godfrey, University of California

Tom J. Henneberry, Don Hendrix, Don Brushwood,Steven E. Naranjo, Steve Castle, USDA-ARS

Robert L. Nichols, Cotton Incorporated

The specter of ‘sticky’ cotton has affected large regions of theworld’s production. Better plant and insect management arekeys to avoiding this costly problem.

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Sticky Cotton Sources &Solutions

AZ1156 – 12/1999

Cooperative Extension IPM Series No. 13

1997, CA cotton growers spent a statewideaverage of $7/A on whitefly control and$38/A on aphid control. Combined, thesecosts accounted for over half of their totalinsect control budget. In TX, aphid andplant sugars have been the largest sourcesof stickiness. TX cotton growers havespent up to $19/A (1995) on aphid controland $21/A (1991) on whitefly control. Inaddition to these immediate costs, exces-sive dependence on chemical control tac-tics carries with it increased frequency andrisks of insecticide resistance with an in-calculable cost to growers and the indus-try.

Sticky cotton can reduce cotton gin out-put (in bales/hr) by up to 25%. At the tex-tile mill, excessive wear and increasedmaintenance of machinery may occur evenwith slightly sticky cotton. In severe in-stances mill shutdown with a thoroughcleanup is required.

A reputation for stickiness has anegative impact on domesticsales, export orders, and prices forcotton from regions suspected ofstickiness. The precise loss ofsales due to stickiness is difficultto estimate, because cotton con-sumption and exports are affectedby many factors every year. Cot-ton price is reduced for stickinessby the market at a rate propor-tional to the perception of risk.Reductions in the market value oflint are applied regionally and in-discriminately. Regional penal-ties are a consequence of the dif-

ficulty in measuring stickiness in cotton.Because there is currently no rapidmethod that is accepted as an indus-try standard for the measurement ofstickiness, there can be no formal,bale-specific schedule of discountsfor stickiness in the USDA-AMScotton classification system. Esti-mates of the immediate effects ofstickiness on regional cotton pricesare reductions up to $0.03–0.05 / lbfor AZ since the whitefly outbreakof 1992 (Fig. 1), and at least $0.03 /lb for West TX in 1995. Since 1992,growers in AZ may have lost as much as$21 million (1993–1995) and $36 million(1996–1998). In West TX, prices were af-fected primarily for the 1995 crop. A simi-lar market penalty could be re-imposed inany region should the potential for sticki-ness be suspected.

In addition to causing price reductions forcotton lint, estimates of losses due towhitefly feeding in southwestern agricul-tural communities exceeded $200 millionin 1991 and $500 million in 1992. In theImperial Valley, CA alone, annual croplosses to the silverleaf whitefly from 1991to 1995 have been estimated to be about$100 million. In 1992 and 1995, whiteflyfeeding directly reduced cotton yields inAZ, as did aphid feeding during the mid-season of 1995 and 1997 in CA.

Stickiness Detection &Measurement

‘Stickiness’ is the physical process of con-taminated lint adhering to equipment (Fig.2). The degree of stickiness depends onthe chemical identity, quantity, and distri-

bution of the sugars, the ambient condi-tions during processing—especially hu-midity—and the machinery itself. Sticki-ness is therefore difficult to measure.Nonetheless, methods for measuring sug-ars on fiber have been and are being de-veloped. These measurements may be cor-related with sticking of contaminated lintto moving machine parts. Currently, nogenerally recognized system of stickinessmeasurement is compatible with the speedof commercial cotton classing. The physi-cal and chemical attributes of the lint andsugars that are correlated with stickinesshave been measured in many ways, eachwith differing efficiency and precision.

Some textile mills use reducing-sugar testsbased on reduction of the cupric ion toscreen for sugar contamination. Thesetests are relatively quick and inexpensive.However, some insect sugars are not re-ducing sugars, and some others are mea-sured at different levels of efficiency byvarious reducing-sugar methods. Thusconventional reducing-sugar tests are bestreserved for screening lint that potentiallyhas high levels of plant sugars. In thesecases and with the potassium ferricyanide(KFeCN) test, lint with reducing sugarlevels below 0.3% may be processed with-out difficulty.

High Performance Liquid Chromatogra-phy (HPLC) identifies and measures bothreducing and nonreducing sugars. Themain sugars of insect honeydew, trehalu-lose (from whiteflies) and melezitose(from aphids), and of plant sugars (glu-cose, fructose & sucrose) are all readilyidentified in this test. The benefit of HPLCanalysis is the identification of the sourceof contamination (whitefly, aphid, orplant) which may help identify specificmitigation measures.

The cotton aphid, Aphis gossypii, excretes honeydew richin melezitose (ca. 30–40%). Their droplets (inset, 50X)tend to be larger than those produced by whiteflies.

Whiteflies, Bemisia spp., also excrete honeydew, butas trehalulose-rich (ca. 40–50%) droplets (inset, 50X).

A preharvest freeze can set off a chain of eventsthat leads to immature fibers and excessiveplant sugars. Inset (250X) are cross sectionsof fibers, normal (left) & immature (right).Note wall thicknesses and lumen volume.

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The physical interaction of all sugars onlint with equipment can be measured byseveral types of machines. The primarydifficulty with these physical tests is instandardizing the stickiness measurement.As with chemical testing, these tests mustbe correlated with measures of fiber pro-cessing efficiency in order to interpret theresults.

One of these tests, the minicard, is a physi-cal test that measures actual cotton sticki-ness of the card web passing betweenstainless steel delivery rollers of a minia-ture carding machine. Modeled after a pro-duction carding machine, the minicardmust be run under strict tolerances (24°C;55% RH). A ‘0’ minicard rating indicatesthat no sticking was observed, while pro-gressively higher numbers (on a 0–3 scale)indicate progressively greater amounts ofsticking during the process. Cottons withhigh plant sugar contents evenly distrib-uted along the fibers may fail to be mea-sured as sticky in this test. The minicardtest is slow and has been replaced as theinternational standard by the manual ther-modetector (see next section).

The Sticky Cotton Thermodetector (SCT)measures the physical sticking pointstransferred to aluminum sheets by a con-ditioned lint sample that is squeezed andheated (to 82.5°C for 12 sec.). Levels ofstickiness are categorized according to the

number of specks left on the twosheets of foil. Lower numbersof specks are preferable tohigher numbers; however, a spe-cific threshold over which allcotton will result in processingproblems has not been defined.The SCT takes about 5 minutesto process each sample, requiressmaller initial investment coststhan the minicard, is more mo-bile, and its results correlatewell with predicted stickinessfrom the minicard.

The High Speed Stickiness De-tector (H2SD) is a quicker, au-tomatic version of the thermo-detector. The cotton sample ispressed between a heated (54°Cfor 30 sec.) and an unheated pressure plate.Sticky points are counted and point sizedistribution determined by image-process-ing computer software. Plates are auto-matically cleaned between samples. TheH2SD is able to analyze a sample in 30seconds.

Like the thermodetector and H2SD, the Fi-ber Contamination Tester (FCT) measuresphysical sticking points (at 65% RH). Theinstrument feeds a thin web between tworollers. Contamination of the rollers inter-rupts a laser beam, resulting in a record-ing. Because the cleaning and recording

is automated, samples may beprocessed as quickly as oneper 45 seconds.

While there is no reliable in-field method for detection ofstickiness predisposition, theinsects responsible for honey-dew deposits can be sampledand populations measured.Not all population levels ofinsects lead to sticky lint;however, chronic numbers ofinsects, especially during bollopening or an extended sea-son, can lead to excessive in-sect sugars that result instickiness. In addition, fieldfactors associated with risk ofexcessive plant sugars arelateness of the crop, fiber im-maturity, and freezing tem-peratures before harvest.

Work is currently underway to determinemethods for measuring insect sugars onfield-collected lint as a tool for predictingstickiness. Such predictions would becomplicated by various degradative pro-cesses that occur prior to processing suchas rain and microbial activity that mightreduce the potential for stickiness.

Managing the Sources

The most efficient way now to preventstickiness is by managing sugar sourcesin the field. Detailed integrated pest man-agement plans (see references) for bothaphid and whitefly have been developedin AZ, CA, and TX. These honeydew-pro-ducing insects may be managed by avoid-ing conditions leading to outbreaks, care-fully sampling pest populations, and usingeffective insecticides when populationsreach predetermined thresholds.

The risk of having excessive plant sugarscan be minimized by harvesting matureseed cotton. This may be accomplishedthrough plant management tactics that in-clude: early and uniform planting, nitro-gen management according to plantgrowth and yield goals, high first-positionboll retention, and timely chemical termi-nation and harvest. If a freeze is imminentand immature bolls are present, the use ofboll-opening chemicals can greatly dimin-ish the problem of plant sugar contamina-tion. All these measures work towardsearly harvest, before freezing conditionsthat contribute to excess plant sugars.

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

-8

-7

-6

-5

-4

-3

-2

-1

0

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ts /

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Calendar Year

1987–1992 = -2.94¢

1993–1998 = -5.63¢

Figure 1. Average† weekly spot price disadvantange ofArizona (DSW) vs. California (SJV) upland(31-3/35). There are other market forces ineffect as well as perception of stickiness.

Table 1. Costs (in $US millions) of aphid and whitefly con-trol in Arizona, California and Texas, 1994–1998(for yield protection & stickiness prevention).

1994

0.0

33.4

11.3

44.7

1995

0.7

25.5

23.0

49.2

1996

0.1

4.8

8.1

13.0

1997

0.0

40.3

9.9

50.2

1998

0.4

2.3

5.5

8.2

Sum

1.2

106.3

57.8

165.3

State

AZ

CA

TX

Sum

27.5

0.0

0.0

27.5

58.1

1.7

9.5

69.3

18.7

3.0

0.0

21.7

17.3

7.9

0.0

25.2

8.9

1.1

0.2

10.2

130.5

13.7

9.7

153.9

AZ

CA

TX

Sum

W H I T E F L Y

A P H I D

† Source: USDA-AMS, Cotton Price Statistics, 1987–1998.

After whitefly-relatedproblems in 1992, AZprices seem to be ad-versely affected by per-ception of stickiness

Mitigating the Problem

When field management of sugar sourcesis inadequate to prevent excess accumu-lation of sugars, mitigation tactics may benecessary to remove excess sugars fromthe lint. This mitigation may be achievedthrough both natural and managed pro-cesses; however, the specific impact ofthese processes on stickiness is variableand may depend on the initial level of con-tamination. Natural processes includeweathering, rainfall, and degradation bymicroorganisms. Since sugars are watersoluble, rainfall will wash some honeydewfrom lint. If sufficient moisture is avail-able, bacteria and molds living on theplants will decompose many honeydewsugars. Complex sugars are broken downto simpler sugars, and the simpler sugars,given sufficient time and moisture, are fur-ther broken down to carbon dioxide andwater. Unfortunately, microbial action alsoleads to discoloration and to a weakeningof the fibers as well as heating of cottonin modules that may result in reduced seedviability and problems in ginning.

Potential in-field mitigation techniques in-clude supplemental oversprays of en-zymes or water. Certain carbohydrate de-grading enzymes when sprayed on stickycotton can reduce honeydew to simplersugars. Microbial activity on the fibersthen further degrades these simpler sug-ars, resulting in a significant decrease infiber stickiness. However, these enzymesrequire water for activity, and metering theproper amount of water for activity is a

The statements contained herein are based on information believed tobe reliable. No guarantee is made of their accuracy, however, and theinformation is given without warranty as to its accuracy or reproduc-ibility either express or implied, and does not authorize use of the infor-mation for purposes of advertisement or product endorsement or certi-fication. The use of trade names does not constitute endorsement of anyproduct mentioned, nor is permission granted to use the name CottonIncorporated, USDA, or The University of Arizona or any of their trade-marks in conjunction with the products involved.

problem yet to be solved. Insome areas of the world,overhead and in-canopy ir-rigation has been used to re-move honeydew from openbolls. The frequency of thistype of irrigation may bemore important than thevolume applied. Use ofsprinklers has been limitedin the Western UnitedStates, where furrow irriga-tion is prevalent.

If stickiness is a problemwhile ginning, the ginningrate of honeydew contami-nated cotton can be in-

creased by increasing the heat of the dry-ing towers to reduce humidity. Thepotential for stickiness can be further re-duced by lint cleaning. Both of these prac-tices, however, can result in shorter fibers.Conventional textile lubricants may alsobe used. Stickiness due to high levels ofplant sugars can be reduced by storing thecotton for approximately six months.However, storage of baled cotton will notappreciably reduce stickiness from insectsugars. At the textile mill, stickiness maybe managed by blending bales and by re-ducing humidity during carding. A lubri-cant in fog form may be introduced at theend of the hopper conveyor, and card-crush rolls may be sprayed sparingly witha lubricant to minimize sticking.

Conclusion

Lints contaminated with sugars from vari-ous sources (plant and insect) can resultin stickiness. Yet stickiness is not an in-trinsic property of the lint and thereforecannot be measured directly. Rather,stickiness is a complex, three-componentinteraction that involves the source sug-ars, harvested seedcotton, and processingequipment. The complexity of this inter-action indicates the need for an integratedsolution that includes prevention, in-fieldmitigation, and processing adjustments.Because currently our best means of elimi-nating stickiness is source sugar minimi-zation in the field, US agricultural researchand implementation agencies continue toemphasize successful insect and crop man-agement plans.

Endorsing OrganizationsThe University of Arizona, The University of Cali-fornia, Texas A&M University, United Stated De-partment of Agriculture, Cotton Incorporated, Na-tional Cotton Council

ReferencesDiehl, J.W., P.C. Ellsworth & S.E. Naranjo. 1997.Whiteflies in Arizona No. 11: Binomial Samplingof Nymphs (rev. 6/97). The University of ArizonaCooperative Extension. 2 pp.

Ellsworth, P.C., J.W. Diehl, T.J. Dennehy & S.E.Naranjo. 1995. Sampling Sweetpotato Whiteflies inCotton. IPM Series No. 2. The University of Ari-zona, Cooperative Extension. Publication #194023.Tucson, AZ. 2 pp.

Ellsworth, P.C., T.J. Dennehy & R.L. Nichols. 1996.Whitefly Management in Arizona Cotton 1996. IPMSeries No. 3. The University of Arizona, Coopera-tive Extension. Publication #196004. Tucson, AZ.2 pp.

Ellsworth, P.C., J.W. Diehl & S.E. Naranjo. 1996.Sampling Sweetpotato Whitefly Nymphs in Cotton.IPM Series No. 6. The University of Arizona, Co-operative Extension. Publication #196006. Tucson,AZ. 2 pp.

Godfrey, L., P. Goodell, E. Grafton-Cardwell, N.Toscano, E.T. Natwick & J. Brazzle. 1998. UC IPMPest Management Guidelines: Cotton. University ofCalifornia DANR Publication 3339. 67 pp.www.ipm.ucdavis.edu/PMG/selectnewpest.cotton.html

Goodell, P.B., L.D. Godfrey, E.E. Grafton-Cardwell,N. Toscano & S. Wright. 1999. Insecticide Resis-tance Management Guidelines in San Joaquin Val-ley. University of California. 21 pp. www.uckac.edu

Slosser, J., J. Leser, D. Rummel, T. Fuchs, E. Bor-ing, M. Muegge & C. Sansone. 1999 Suggestionsfor Management of Cotton Aphid in West Texas.en towww. tamu .edu /ex tens ion /bu l l e t i ns /aphweb99.html.

For more information about cotton sticki-ness and insect/crop management, includ-ing this publication, visit the internet site:ag.arizona.edu/cotton.

Funding for the printing of this bulletinwas provided by Cotton Incorporated.

StickyCotton

Figure 2. ‘Sticky’ cotton is a complex, 3-component inter-action among source (insect or plant sugars), lint,and processing equipment.

Issued in furtherance of Cooperative Extension work, acts of May 8and June 30, 1914, in cooperation with the U.S. Department of Agri-culture, James A. Christenson, Director, Cooperative Extension, Col-lege of Agriculture, The University of Arizona.

The University of Arizona is an equal opportunity employer authorizedto provide research, educational information and other services only toindividuals and institutions that function without regard to sex, race,religion, color, national origin, age, Vietnam Era Veteran’s status, ordisability.

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