J. Michael Moore
Production of
Tops and Suckers
Benefits of Topping and
Sucker Control
Topping
Chemical Sucker Control
Topping and
Chemical Sucker Control Programs
Minimize MH Residues
Table 1: Tobacco Sucker Control Chemicals
Table 2. Yellowing Agent for Flue-Cured Tobacco
Tobacco produces a single stalk with a terminal or apical bud at the top. The terminal bud exhibits apical dominance. At each leaf axil lateral buds may be produced if the terminal bud is lost, removed or allowed to go completely to the production of flowers.These lateral buds are called "suckers" and grow especially fast after the removal of the terminal bud and the loss of apical dominance.
After apical dominance is lost suckers in the top three or four leaf axils begin to grow. There is a potential for the production of three suckers in each leaf axil. As long as the primary sucker is allowed to grow the others generally do not begin to grow. If the growth of the primary sucker is controlled or the sucker removed, the next sucker in the leaf axil will begin to grow. The goal of chemical sucker control should be to control as many of the suckers as possible in each leaf axil before the sucker begins to grow.
Removal of the tops along with the removal or restriction of sucker growth results in certain desirable changes in the cured leaf. Benefits of topping and sucker control include; increased root growth, reduced weight in the top of the plant, a reduction of the translocation of nutrients and moisture from lower leaves to support the growth and development of upper leaves. Increased root growth means an increase in the potential for uptake of water and nutrients, increased support for the upper plant against wind, and an increase in the plant's potential to synthesize nicotine. Topping can remove significant weight and wind foil from the top of the plant and prevent the plant from being blown over during wind gusts or rain storms. As long as the terminal bud remains in place the plant will rob from lower leaves to support the development of flowers and production of seeds. Once apical dominance is broken, there is more support for the upper leaves and less drain on the lower leaves.
Topping, and the time of topping, can have a significant effect on the physical and chemical nature of cured leaf. Topping improves yield, increases price and value per acre, and increases the alkaloid and sugar content of cured leaf. Topping in combination with removal of suckers can increase yield, alkaloids and sugars more significantly than topping alone when compared to the not-topped plant. To obtain maximum yield and financial returns tobacco must be topped and the suckers controlled. Topping and sucker control may be by removal, either by hand or machine, or by the use of plant growth regulator chemicals.
Most tobacco varieties will produce a maximum of yield and quality when the top is removed after the production of 18 to 22 leaves. Any excess foliage or floral growth beyond this point is removed and thrown on the ground and is of no benefit to the plant or financially to the grower. The goal should be to remove as little from the top of the plant as possible as soon as possible and to minimize the production of suckers which also take away from maximum yield production and require hand labor to remove them. Topping at lower leaf numbers reduces leaf area per plant and increases the concentration of nicotine.
As the tobacco plant changes from the vegetative state to the reproductive state the bud under goes a developmental change from production of leaves and becomes a flower. This transformation takes approximately 21 days from the "button stage" when the bud is visible in the center of the plant as a "button" or "ball" of unopened florets until the "late flower stage" when all of the florets in the top have flowered and some are shedding. Following the button stage, approximately seven days later, and the next stage of development is the "early flower stage" when only a few florets are beginning to open and show the white color of the flowers. Seven days later is the "full flower stage." During this progression the plant continually channels water and nutrients to the terminal bud to insure production of flowers and the eventual reproduction of the species as seeds. As the tobacco plant is allowed to progress from one stage to the next the top continues to rob the plant and the producer of yield and quality.
Yield and price/cwt is lowered when topping is delayed beyond the early flower stage. Total alkaloid content is reduced as topping time is delayed, except from the full to late flowering stage, and sugar content is lowered with delayed topping after the early flower stage. Total nitrogen content is not materially affected by topping time. The number and weight of suckers are reduced by delays in topping. Leaves from plants topped earlier will be thicker, and have more oil and body, especially those in the upper part of the plant.
When topping is combined with chemical sucker control rater than hand removal of suckers yield is improved. Topping in the button stage with chemical sucker control rather than topping in the early flower stage increases yield. A number of other benefits of topping at the button stage make this the ideal time to perform this task. In most instances topping at the button stage will occur prior to beginning harvest. This allows for better utilization of labor and reduces the need to be performing the two tasks at the same time. When the top is not allowed to develop beyond the button stage the threat of top heavy plants being blown over by windstorms is considerably reduced. Early topping will stimulate further root growth and will further anchor the plant against wind as well as improve the plant's ability to survive dry soil conditions. Early topping also serves to remove some of the attraction to the plant of numerous insect pests which spread a number of virus diseases such as tomato spotted wilt virus as well as those which lay eggs that hatch into feeding insects. Reducing insect populations can reduce insecticide costs, residues and hazards to laborers as well as reducing potential disease losses.
Although tobacco plants are typically topped either by hand or mechanically, topping may be accomplished chemically before the emergence of the button and opening of any flowers. Chemical topping would appear to be the ideal method for eliminating the production of excess leaves and the top which will flower. The presence of a percentage of plants which are chemically topped by the application of contact fatty alcohol materials is an indication that the application occurred on a timely basis and the solution concentration was strong enough to kill suckers. With strong solution concentrations a higher percentage of suckers are killed in leaf axils contacted by the solution. Chemical topping of plants in the prebutton stage eliminates the production of excess leaves and tops which are discarded and do not add to yield of cured leaf. Plant resources can now be concentrated to produce fewer, larger, thicker and heavier leaves. Leaf body can be increased by early chemical topping and redirection of these plant resources.
Tobacco should be topped early during periods of drought to maximize leaf production from already short soil and plant moisture supplies as well as to stimulate further root growth and greater moisture update potential.
Tobacco should also be topped early under conditions of excess soil moisture. Again, the plants will benefit from the root growth which is stimulated by removal of the top. Sometimes this additional root growth will be needed to to replace roots which have rotted and have reduced the moisture uptake to support the upper plant to 40 percent of normal. This reduction in water uptake when the plant is also under stress from extreme heat can lead to wilting and collapse of the leaves. Prolonged wilting can result in loss of leaves or portions of leaves.
Tobacco which has been over fertilized with excess nitrogen has a tendency to produce a thin leaf. Topping excessively fertilized plants at a higher leaf number can lead to a greater number of thin leaves. Normal topping height may be effective in causing these thin leaves to thicken up with time. However, the high availability of nitrogen will drive the production of suckers and sucker growth. An aggressive sucker control program is required.
Three types of sucker control chemicals are available for use by tobacco growers in the United States. They are Contacts, Systemics, and Contact-localized-systemics. A knowledge of how the various sucker control chemicals work is important to obtaining optimum control. Once how the chemicals work is understood, the stage of plant development for optimum sucker control with each chemical must also be kept in mind.
Contacts are fatty alcohols (C10 or a mixture of C6-C12 alcohols) and act by giving contact kill of suckers smaller than 1 to 1.5 inches in length. First, the waxy coating which retains water in the tender growth of the sucker is broken down by the contact. Then, in the full sunlight the sucker gives off more water than the plant can replace causing the sucker to turn brown, dry up and die. Sucker growth that is too large may not be killed because of a thicker waxy protective coating.
Multiple applications of contact fatty alcohols are normally used to kill young suckers up to one and one half inches long which develop in the top of the plant as the button emerges and the flower develops. Applications usually are made on a five to seven day schedule at increasing solution concentrations to follow the growth of new suckers as new leaves emerge. As the tissues in the bud grow older, the waxy coating on them increase and less damage is caused by greater concentration of fatty alcohols. Multiple applications also allow time for plants in the same field to have reached the same stage of development and for the upper leaves to develop to a sufficient size which will not be damaged by future applications of other sucker control chemicals which inhibit cell division.
The concentration of the contact solution is of primary importance in obtaining sucker control. It is important that contacts are mixed in the proper proportions before spraying onto the field. The contact sucker control materials containing fatty alcohol are the only chemicals that must be mixed with water in the proper proportions to be effective. Solution concentrations used typically range from three to five percent. The effectiveness of sucker control will be reduced if the concentration of the contact solution is too weak. Weak contact solutions may cause superficial damage to suckers in the short term and result in poor, late-season sucker control. Although the effectiveness of sucker control by contact solutions is considerably improved by increasing concentration, if the concentration is too great, the solution may cause leaves to be burned and excessive injury to leaf axils. Excessively burned leaf axils may serve as entry sites for certain disease organisms and may be weakened resulting in the loss of heavy leaves.
At least three suckers may grow from the area in which the leaf and the stalk join. It IS possible to control suckers that have not developed to the point that they may be seen. However, this again calls for proper concentration of contact material. In other words, the solution must be hot enough to burn beyond the sucker you can see and to dry up the tiny suckers which have not yet developed to the point you can see them.
In uniformly growing tobacco, the first application of a contact sucker control chemical should be made when 40 to 50 percent of the plants in the field have reached the early button stage. This initial application of contact fatty alcohol will burn out small suckers that are beginning to grow and will allow the field to become more uniform as additional plants come into button and full flower stages of development. At least 5 to 10 percent of the plants should have their buds burned out by the initial application of contact. If some buds are not burned out the application was applied later than optimal or was not mixed at a high enough concentration.
The first application of contact should contain at least one and one half gallons of contact for each 48.5 gallons of water (3% solution) to be effective. Later applications should contain two to two and one half gallons of contact per 48 to 47.5 gallons of water (4% to 5% solutions). At least two and possibly three applications of contact applied on a five to seven day schedule may be required to keep sucker growth from becoming a problem.
Other factors also affect the burning appearance of contact solutions. Tender sucker tissues may be burned by weaker contact fatty alcohol solutions. Older, larger, sucker growth may require the use to stronger solutions. Bright, sunny conditions when temperatures are high promote better effectiveness of contacts. The concentration of contact fatty alcohol used may need to vary based on the time of day, degree of cloudiness, temperature and previous soil moisture status under which sucker growth has been produced.
Tops containing at least one flower should be removed after each application of contact chemical. Allowing tops, suckers and flowers to remain on the tobacco plants until the full field is in full flower has been determined to result in the loss of 27 pounds per acre per day of saleable tobacco.
Contacts should be applied at relatively low pressure, (20 to 25 psi) with nozzles which deliver large droplets (solid cone type) in sufficient volume (50 gallons per acre) to cause the solution to run down the leaf midribs to the stalk and wet each leaf axil all the way to the soil surface. Hand application of contacts with a single nozzle or poured from a jug is also possible and may be necessary for small operations or under circumstances where plants in the same field are not uniform. Plants must be uniformly standing in an upright position to allow the solution to run around the stalk to leaf axils on all sides. Contact solutions should be continuously agitated to insure that the lighter than water alcohols stay mixed in solution.
Systemics enter the plant and travel throughout the plant stopping cell division and therefore stopping the growth of young, tender, rapidly growing, tissue such as suckers. Maleic hydrazide (MH) is the systemic used. MH is taken up most readily by the youngest most rapidly growing portion of the plant, generally the top one third of the plant, and gives long-term control of sucker growth. MH is most effective when applied to a plant which has been actively growing under good moisture conditions. Absorption is also better when temperatures are not too extreme and stomata are not closed such as in the mornings after the dew has dried.
After MH application, large suckers that are already present develop much slower and with very narrow leaves. Upper plant leaves which are at least 10 to 12 inches long develop to their normal size because of continued cell elongation even though cell division has stopped. Further development of existing suckers occurs at a reduced rate.
Under normal growing conditions MH will control the growth of new suckers for only about six weeks after application. Since the time between topping and the final harvest is usually greater than six weeks, scheduling of the MH application is important. Timing and the number of applications of contacts can be used to delay the time of MH application beyond the first harvest, thus shifting the window of control to cover a later part of the season.
Currently produced varieties have better root systems, are more disease resistant, respond to higher fertilization and mature later than older varieties and may remain in the field for longer periods of time. Control can be further improved and longevity of control extended beyond that normally expected of MH alone by including a contact-localized-systemic such as Prime+ or Butralin in the sucker control program. The contact-localized-systemic can be applied either in a separate application before or after MH, or as a tankmix with MH.
When MH is applied alone, the goal of the application procedure should be to wet the upper surfaces of the leaves in the top one third of the plant. Application pressure should be 25 to 30 psi and 30 to 35 gallons per acre of spray solution should be directed toward the top of the plant with nozzles which deliver medium sized droplets (small solid cones). Care should be taken not the apply the solution to the lower stalk positions which will be harvested soon.
MH residues are greater in tobacco than are the residues for any other pesticide used on tobacco. These relatively higher residues are of concern to manufacturers because of the requirements of some countries for final manufactured products with limited MH residue levels. These restrictions appear to be based on the relatively high residue numbers for MH in tobacco rather than on real and specific justifications. MH has recently been reregistered by the Environmental Protection Agency and has been shown not to be a cause of health problems.
Average MH residues have been reduced significantly in United States produced tobacco in the last seven years by growers who have begun to utilize alternative chemical sucker control programs which do not place primary sucker control emphasis on MH alone. MH use rates have been reduced and sucker control has actually improved with the incorporation of timely applications of contacts and contact-localized-systemics in the sucker control programs. In addition, changes in MH application procedure and timing have changed to take advantage of naturally occurring conditions which can help to reduce residues. Application of MH following the first harvest means that the MH residues in the first harvest are zero. By waiting to harvest after MH application until rainfall or irrigation has occurred can also be effective in reducing residues by as much as half.
Tankmixes of contact and MH may be applied in place of the normal MH to provide additional burnout of small suckers which may not be adequately controlled by MH alone. At least two premixes of these materials are available, but the individual materials may be mixed in the tank to provide the desired MH and contact solution. A four to five percent contact solution is recommended. Application procedure should be that described for application of contact solution. The top leaves will receive adequate MH from the solution which covers them.
Contact-localized-systemics such as flumetralin (Prime+) and burtralin (Butralin) must be applied directly to the leaf axil where suckers grow and works systemically in the local leaf axil by stopping cell division and preventing sucker growth. Contact-localized-systemics do not move readily throughout the plant. For this reason contact-loalized-systemics must be applied to wet each leaf axil as any leaf axils that are missed will grow large suckers which must be removed by hand. Contact-loalized-systemics do not cause suckers to turn brown and dry up, but causes small suckers to turn to a pale green and become constricted with minimal further growth.
Access to these three types of chemical materials has lead to the development of a number of sucker control programs which utilize the advantages of each type of material by application at specific times in the development of the plant and the sucker. All programs depend on uniform application of only the needed nitrogen fertilizer which should allow normal ripening of the crop without delaying maturity or unnecessarily promoting sucker grow. Applications containing mixes of two or more of these chemical types may be useful in obtaining maximum sucker control.
Good sucker control increases yield and quality, helps reduce foreign matter in harvested tobacco, improves the efficiency of harvesting and handling, and may improve the grade and price of tobacco at auction. In order to effectively control suckers the crop must not be over-fertilized and the application of sucker control chemicals must start early (when 40 to 50 percent of the plants are in the early button stage) and be continued on a timely basis (5 to 7 days between contacts and 5 to 7 days between contacts and MH or a contact localized systemic.
The following topping and chemical sucker control programs have been used successfully by tobacco growers. Their effectiveness depends on timely treatment and application of the correct rate of nitrogen with non-excessive adjustments for leaching. Excessive nitrogen applications often result in sucker growth which is uncontrollable with any of the chemicals available.
Step 1.
Apply the first of at least two contact sucker control (Off Shoot T, Contact-85, Sucker Plucker, Fair 85, etc.) treatments when 40 to 50% of the plants are in the early button stage.
Step 2.
Top flowering plants as soon as the contact solution has dried on the plants after each application.
Step 3.
Make a third application of contact 5-7 days following the initial treatment to remove suckers that have grown out since the first application. A 5 % concentration may be used for the third application (2.5 gallons of contact in 47.5 gallons of water).
Step 4.
Top all remaining plants following the final contact application.
Step 5.
Some tobacco purchasers have established limits for MH in either their finished cigarettes or tobacco before manufacturing. Because of the global nature of the tobacco industry, all buying companies are being forced to monitor the MH residues of tobacco they purchase. MH residues can be related directly to use rate, reapplication, application method, and time and rainfall occurring between application of MH and harvest. While it is not yet feasible to determine the residue level of an individual grower's tobacco prior to auction, each pile can be traced back to the producer. Buying companies are aware of the MH residues associated with individual markets and may leave a market known to have higher than acceptable levels. Growers are encouraged to follow the label instructions for applying all pesticides for the good of the entire industry.
| Mean maleic hydrazide (MH) residues (ppm) for flue-cured tobacco by belt and year. | |||||||||||
| TYPE | 1988 |
1989 |
1990 |
1991 |
1992 |
1993 |
1994 |
1995 |
1996 |
1997 |
1998 |
| 14 (GA/FL) | 192 |
178 |
196 |
200 |
118 |
139 |
128 |
119 |
120 |
130 |
194 |
| 13(SC) | 136 |
159 |
211 |
183 |
143 |
131 |
124 |
94 |
96 |
140 |
164 |
| 13(NC) | 103 |
127 |
163 |
210 |
137 |
148 |
128 |
120 |
90 |
140 |
194 |
| 12(NC) | 146 |
144 |
168 |
138 |
135 |
141 |
117 |
114 |
89 |
153 |
140 |
| 11-B(NC) | 73 |
110 |
109 |
103 |
124 |
104 |
112 |
114 |
75 |
93 |
118 |
| 11-A(NC) | 69 |
66 |
85 |
74 |
42 |
45 |
37 |
80 |
58 |
44 |
33 |
| 11-A(VA) | 62 |
34 |
28 |
76 |
38 |
48 |
34 |
39 |
41 |
41 |
42 |
| AVERAGE | 143 |
124 |
147 |
140 |
115 |
117 |
103 |
101 |
85 |
120 |
132 |
Table 2. Yellowing Agent for Flue-Cured Tobacco
| Chemical Type | Chemical and Formulation | Rate per Acre | Remarks and Precautions |
| YELLOWING AGENT | ethephon (Ethrel) 2 lb/gal ethephon |
2 - 4 qt 1.33 - 2.66 pt |
Use after second or third priming when remaining leaves are physiologically mature. Directed Spray: Mix the lower amount in 50 to 60 gal of water and apply on a warm, sunny day as a fine spray mist with drop nozzles which direct the spray so that all mature leaves are covered. This treatment may make determining which leaves to harvest a little difficult as the tips of some upper leaves may yellow more rapidly than the butts. Harvest all leaves with 20% or more yellowing. Over the Top: Use the higher rate in 40 to 60 gal of water for an acreage of coverage. Apply to all remaining leaves on the stalk. Determining time of application requires some experience and some trial and error; therefore, use a test kit to treat a few plants and observe the results before treating the whole field. Harvest yellowed leaves when they reach desired degree of yellowness, usually within 24 to 72 hours. Harvest may be completed the day after treatment. Excessive delay in harvest may result in loss of yield and quality or leaf drop. Tobacco which is sufficiently mature when treated and which yellows prior to harvest may require an advanced curing schedule with reduced yellowing time. Close attention should be paid to the curing schedule. |
Trade names are used only for information. The Cooperative Extension Service, the University of Georgia College of Agricultural & Environmental Sciences, does not guarantee or warrant published standards on any product mentioned; neither does the use of a trade or brand name imply approval of any product to the exclusion of others that may also be suitable.
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