Removing leaves and opening bolls with harvest aids are important components of a management plan for producing high-quality cotton fiber. When not properly managed, harvest aids may reduce yield and quality. By properly managing the time of defoliation, the crop can be prepared for a timely harvest, which is critical in Missouri's short season environment. The number of suitable hours for harvest operations decreases rapidly during the fall. With timely harvest, earlier stalk destruction can occur as an essential part of insect and disease management. The objective of this publication is to provide information on proper defoliation techniques and the available harvest aids on the market today.David W. Albers (State Extension Specialist-Cotton, Delta Center), Fred Fishel (Pesticide Application Trainer Supervisor), Jill B. Mobley (Research Specialist).New March 199

Albers, David W.

Fishel, Fred

Mobley, Jill B.

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University of Missouri ExtensionG4253, New March 1994Cotton Harvest AidsDavid W. AlbersState Extension Specialist-CottonFred FishelPesticide Application Trainer Supervisor,Jill B. MobleyResearch SpecialistNoteMention of a trade name in this publication does not constitute a guarantee or warranty of the product by MU and does notimply its approval to the exclusion of other products that also may be suitable.Removing leaves and opening bolls with harvest aids are important components of a management plan forproducing high-quality cotton fiber. When not properly managed, harvest aids may reduce yield and quality.Some of the benefits of defoliation include:Increases exposure of bolls to sunlight, which causes faster drying and opening.Picking operations can begin earlier in the day due to faster drying.Reduces trash and green leaf stain (improves grades).Reduces boll rot.By properly managing the time of defoliation, the crop can be prepared for a timely harvest, which is criticalin Missouri's short season environment. The number of suitable hours for harvest operations decreases rapidlyduring the fall. With timely harvest, earlier stalk destruction can occur as an essential part of insect anddisease management. The objective of this publication is to provide information on proper defoliationtechniques and the available harvest aids on the market today.Timing of defoliationDo not defoliate too early. Micronaire reduction, reduced oil content of seed, lower seed viability and yieldreduction may occur. Some of the more traditional methods for determining time of defoliation include:Boll firmness.Percent open bolls.Seed coat coloration.Heat unit accumulation.Visual assessment.Defoliation time can be planned earlier in the season by using plant mapping techniques. When plants reachthe stage of 4 to 5 nodes above white flower (NAWF), they have reached the end of the effective boll loadingperiod or "cutout." Knowing that approximately four to six weeks or 750 to 850 heat units will be required forboll maturity, a producer can then begin to make harvest aid decisions. Recent research has demonstrated thatG4253 Cotton Harvest Aids | University of Missouri Extension http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...1 of 5 6/10/2010 12:45 PMcotton can be defoliated with no loss in yield or quality when 3 to 4 nodes with harvestable bolls are presentabove the uppermost, first position cracked boll. Plant mapping techniques will be most useful in fields thathave uniform stands, early fruiting initiation and high fruit retention.These techniques should not replace visual verification of crop maturity status, however. The general practiceis still to wait until at least, on average, 60 percent of the bolls are open prior to applying any harvest aidmaterials. Another excellent check of crop maturity is to cut the top bolls that you hope to harvest. If thesebolls have a dark-colored seed coat and the seed is no longer jelly-filled but has developed well-definedcotyledons, then the fiber on that boll is mature and safe for harvest aid application. Use of the 60 percentrule and boll inspection in conjunction with plant mapping techniques will aid a producer in making propercrop termination decisions.NoteDon't hurry a harvest aid decision and make a mistake that may cost yield and fiber qualityEnd of season scenariosFor a cotton crop to reach maturity in a timely matter requires more than just good harvest aids. The croprequires management for timely cutout and maturity from the time it is planted. A good date to reach cutoutin Missouri is Aug. 10, since blooms formed after that date have a much smaller chance of maturing; notenough heat units are received during most seasons. Blooms formed before Aug. 10 have a much greaterchance of maturing. In fact, under average conditions at Portageville, Mo., blooms that open on Aug. 1should, on average, mature between Sept. 10 and 20, while an Aug. 10 bloom won't be mature until Oct. 1 orlater. The accumulation of heat units in October is very minimal, so little boll growth and maturity is possibleduring that month in most years.Managing end-of-season decisions is determined by a combination of crop maturity, temperatures suitable forharvest aids to work, and good field conditions for picking 10 to 14 days after the harvest aids were applied.In general, harvest aids (defoliants and boll openers) work best when the average temperatures stay above 60degrees Fahrenheit. September is the prime defoliation period, with average temperature remaining above 60degrees Fahrenheit for most of the month (Table 1). After mid-October the chances of receiving temperaturessuitable for defoliants and boll openers drops to less than 1 in 3. The rainfall pattern during September andOctober is variable, but early October appears to be drier than the other weeks. Cotton harvest during earlyOctober could take advantage of the slightly drier pattern.Table 1Temperature and rainfall pattern during September and October at Portageville, MoMonth Days suitable forfieldwork*Chance of receiving > 59degrees FahrenheitAverage minimumtemperatureAverage maximumtemperatureWeeklyrainfallSeptember First week: 5.45 100 percent 64 degreesFahrenheit74 degreesFahrenheit0.81 inchSecond week:5.55100 percent 62 degreesFahrenheit72 degreesFahrenheit0.85 inchThird week: 5.36 92 percent 60 degreesFahrenheit70 degreesFahrenheit0.87 inchFourth week: 5.27 84 percent 56 degreesFahrenheit67 degreesFahrenheit1.00 inchG4253 Cotton Harvest Aids | University of Missouri Extension http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...2 of 5 6/10/2010 12:45 PMOctober First week: 5.65 73 percent 50 degreesFahrenheit63 degreesFahrenheit0.53 inchSecond week:5.6365 percent 49 degreesFahrenheit61 degreesFahrenheit0.82 inchThird week: 4.15 31 percent 46 degreesFahrenheit58 degreesFahrenheit0.85 inchFourth week: 4.21 26 percent 44 degreesFahrenheit55 degreesFahrenheit0.69 inchFifth week: 4.09  45 degreesFahrenheit57 degreesFahrenheit0.84 inch*Days suitable for field work is averaged from 12 years of data for southeastern Missouri.Temperature probabilities are an average for 26 years in Portageville, Missouri.Picking the best harvest aid materialEnvironmental conditions at the time of defoliant application and for three to five days following can have atremendous influence on the effectiveness of these chemicals. Under conditions of high sunlight, temperatureand relative humidity, defoliants are most active. A night temperature of at least 60 degrees Fahrenheit isparticularly important. Early research indicates that defoliation proceeds twice as rapidly at 95 degreesFahrenheit than at 77 degrees Fahrenheit. Most harvest aids need minimum temperatures above 55 to 65degrees Fahrenheit for optimal performance. If temperatures drop below this level, then leaf drop and bollopening will be slowed. High relative humidity is important for lower evaporation and transpiration will allowbetter absorption of the chemical defoliant into the leaf.Each harvest aid material has its own strengths and weaknesses and should be used with conditions and atrates that will produce the desired defoliation and boll opening. The condition of the crop and the weatherforecast are important factors when selecting a defoliant. Table 2 provides a description of the commonlyused harvest aids for Missouri.Table 2Description of harvest aid materialsProduct(formulation)Description RatesDef 6 or Folex (6pounds a.i. pergallon)Defoliant used over a broad range of conditions. Reduce rates iftemperatures are warm (85 degrees Fahrenheit or higher) to avoid "stuck"leaves. Is very effective when used in combination with Prep.1.33 to 2 pints peracreHarvade (5 poundsa.i. per gallon)Defoliant that removes leaves while still green, but can also help dry upmorningglory vines is the field. Always use with crop oil concentrate.0.5 pint per acre + 1pint crop oil conc.Dropp (50 percenta.i. WP)Defoliant that works best in warm weather (average temperature near 70degrees Fahrenheit). Effectively suppresses regrowth. Cool weather activitycan be improved when used in combination with Prep. Activity may also beincreased by using ammonium sulfate or silicone-based spray adjuvant.0.2 to 0.4 pounds peracrePrep (6 pounds a.i.per gallon)Boll opening compound that also causes some defoliation. This compoundtypically should be applied after defoliants or tank-mixed with defoliants.Should not be applied until all harvestable bolls are mature to avoid reducingyield and fiber quality. Allow 14 to 21 days between application and harvestfor complete boll opening.1.33 to 2.67 pints peracreG4253 Cotton Harvest Aids | University of Missouri Extension http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...3 of 5 6/10/2010 12:45 PMStarfire (1.5pounds a.i. pergallon)A desiccant material with active ingredient paraquat. Can help open bolls.Needs to be used in combination with a defoliant. Restricted Use Pesticide.4 to 6 ounces peracre in combinationwith other defoliantsQuick Pick (3.1pounds a.i. pergallon)A desiccant material that can help improve defoliation when used incombination with defoliants and Prep.1 pint per acre incombinationsSodium Chlorate (6pounds a.i. pergallon)A desiccant that can defoliate cotton, but causes some "stuck" leaves. 4.5 pound per acre or3 quarts per acrePicking the right harvest aid strategyDefoliation is as much an art as a science, since many variables of crop and weather conditions interact in thefinal performance measured in terms of leaf drop, regrowth, boll opening, yield and fiber quality. To simplifythe decision somewhat, we will discuss only the variables that can be readily recognized or controlled.Canopy/crop sizeOne of the first considerations is how large a canopy of leaves needs to be removed. If the crop is taller than40 to 45 inches tall, some difficulty may be experienced in removing all the leaves with one application of adefoliant. If a tall crop is not ready to defoliate until late September or October when the temperatures are notconducive for quick leaf drop and boll opening, then higher rates and spray volume may be needed. Theseconditions are also conducive to boll rot. Managing for final plant height to equal row spacing has been shownto result in less yield loss to boll rot. A plant of manageable size should result in better spray coverage andmore effective defoliation.Leaf/crop maturityIf the leaves have remained green or new young leaves have been added to the plant after cutout, then careshould be given to avoid "sticking" leaves by applying too high a rate of defoliant. The greatest potentialproblem is experienced with warm temperatures (greater than 85 degrees Fahrenheit) for areas of the fieldthat have remained green. It may also be possible to reduce the rate of harvest aid if the canopy has maturedand already experienced some natural leaf aging with warm temperatures.TemperatureThe activity of defoliants depends largely on the temperature experienced during the period three to five daysafter the material is applied. Average temperatures above 60 to 65 degrees Fahrenheit greatly enhancedefoliant activity. Some materials such as Def, Folex, Harvade and Sodium Chlorate can defoliate cottonleaves under cool conditions, while Dropp is extremely sensitive to cool conditions. When cool conditions areencountered, a combination of materials is recommended, typically a defoliant and a boll opener. Theeffectiveness of harvest aids under both warm and cool conditions are summarized in Table 3.Table 3Effectiveness of harvest aids for defoliation, boll opening and regrowth control under warm and cool conditions in MissouriDefoliant/rate Cool conditions (less than 60degrees Fahrenheit average)Warm conditions (more than 65degrees Fahrenheit average)Defoliant1Boll opening1Defoliant1Boll opening1Def or Folex 1.3 pint per acre 7 6 9 8Dropp 0.2 pound per acre 3 6 9 8G4253 Cotton Harvest Aids | University of Missouri Extension http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...4 of 5 6/10/2010 12:45 PMHarvade 0.5 pint per acre + Crop Oil 1pint per acre7 6 9 8Prep 1.5 to 2 pints per acre 5 7 8 9Prep 1.5 to 2 pints per acre + Def orFolex 1.3 pints per acre8 7 9 9Prep 1.5 to 2 pints per acre + Harvade0.5 pint per acre + Crop Oil 1 pint peracre8 7 9 9Prep 1.5 to 2 pints per acre + Dropp 0.1to 0.15 pounds per acre8 7 9 9Prep 1.5 to 2 pints per acre + Quick Pick1.0 pint per acre7 7 9 9Starfire 4 to 6 ounces per acre +Harvade 0.5 pint per acre8 6 8 9Sodium chlorate 3 quarts per acre 7 7 8 81Ratings for defoliation and boll opening on a scale of 0 = none to 9 = excellent.Yield potentialUnder conditions of above-average yield potential and profitability, using a combination of a defoliant andboll opener, e.g. Prep + Def or Folex, can provide a rapid, thorough defoliation and opening of bolls for alarge first harvest. Using a combination approach is more expensive, but if the potential return of high-qualitylint is in the field, this approach will permit the greatest return. In contrast, if the potential yields are not greatfor a crop that has experienced water stress, then using a less expensive harvest aid strategy should providethe greatest economic return.Picking once or twiceComplete defoliation and boll opening generally permit quicker harvest of cotton with less trash. The cost of acombination of Prep and a defoliant that can produce once-over harvest is $30 per acre less expensive than asecond harvest operation. The fiber harvested with the once-over strategy is typically of higher quality andvalue.G4253, new March 1994Related MU Extension publicationsG4268, Cotton Plant Development and Plant Mappinghttp://extension.missouri.edu/publications/DisplayPub.aspx?P=G4268Order publications online at http://extension.missouri.edu/explore/shop/ or call toll-free 800-292-0969.G4253 Cotton Harvest Aids | University of Missouri Extension http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...5 of 5 6/10/2010 12:45 PM

Cotton harvest aids (1994)

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