TOPPING, SUCKER CONTROL AND HARVEST TIME FOR BURLEY TOBACCO

Gary Palmer

Topping

One key to achieving the quality of burley tobacco demanded in today's market is proper topping time. Old University of Kentucky publications promoted late topping because early topping produced heavy bodied, darker tobacco. Now good quality heavier bodied, darker tobacco is in greater demand than thinner, buff colored tobacco.

Once blooming begins plant energy moves to the bloom for seed production at the expense of leaf production. Removing the bloom will redirect energy to leaf production.

For most burley tobacco varieties topping when only 10 to 25% of the plants in a field have one flower open will produce the best results. Producers often misinterpret the 10 to 25% recommendation as the percentage of plants in full bloom. A field of burley tobacco that has only 10 to 25% of its plants with one flower open will look early to farmers that are use to topping late. Late maturing varieties like TN 86 and KY 8959 tend to respond well to bud topping. Bud topping may reduce yields in other varieties.

Certain varieties like TN 86 tend to produce flashy, poorer quality tobacco. Other varieties may also have a tendency to produce a lighter, thinner bodied tobacco. These varieties are more likely to develop better quality if topped early.

Early topping will not affect yields if other factors such as harvest time after topping remain constant. In addition to improvements in quality, topping at early bloom reduces sucker pressure. This is especially true for L8 hybrids that initiate sucker growth early. Since sucker development will be slight or non-existent at an early bloom stage, sucker control will be easier. Many sucker control problems are due to failure to remove suckers that have already developed beyond the size that can be control by sucker control chemicals. Because the stalk is tender and immature at this stage, topping time decreases. A clean break can mean less hollow stalk.

An early topping schedule can be an important component in an aphid management program. Removing the top before aphid populations peak could prevent excessive buildup and prevent yield loss. Aphids removed with the top can not move back up the plant.

Leaf Number

To achieve the optimum results from early topping, top down to the right number of leaves for the variety being used. Producers have a tendency to leave too many leaves. Extra leaves increase stripping labor and may increase the incidence of houseburn in old barns that have less space between tiers. Many producers think that extra leaves mean extra yield. These extra leaves not only take away from leaves lower on the stalk, but fail to develop properly.

Most varieties need only 20 leaves to produce good quality and yields. KY 14 X L8 and other L8 hybrids need only 18 leaves whereas TN 86 requires 22. Once topping height has been determined, top all plants to a similar leaf size. In many cases, discarding large leaves seems wasteful, but it is necessary to achieve optimum results. Even though it may be hard for some producers to bring themselves to throw away seemingly good leaves, most leaf spread will occur after topping. Growth of remaining leaves will more than compensate for those removed.

Sucker Control

Three types of chemical sprays for controlling sucker growth on tobacco plants are: 1) Systemic - absorbed by plants and move inside the plant to active growth sites, 2) Contact - not absorbed by plants requiring direct contact with suckers _3) Local systemic - absorbed locally by suckers, but requires contact with the sucker. Application methods for the three types of chemicals differ.

Systemic chemicals

The systemic chemicals contain maleic hydrazide (MH) as the active ingredient. Maleic hydrazide used at the proper rate does not kill suckers but prevents additional growth. Plants topped to a leaf that is no smaller than 6 inches long should spread normally.

When to Use

Topping when 10 to 25% of plants in the field h ave at least one flower open produces the best results. Remove all suckers present when topping. Although application of a systemic chemical immediately after topping performs best, but other combinations of topping and chemical applications may work as well. Applications followed by topping within two days produces satisfactory results.

How to Apply

When applying MH, use labeled rates (1.5 to 2 gal per acre) added to water to achieve a total spray volume of 30 to 50 gal/acre. New information favors a coarse spray over a fine spray for best results. For sprayers designed to run 4 to 5 mph, TG-5, CE-5 or equivalent full cone nozzles spaced 20 inches apart with a pressure of 20 to 25 PSI provide good coverage. For sprayers designed to run slower, 3 to 3.5 mph, use TG-3, CE-3 or equivalent nozzles at the same pressure. It is not necessary to spray the entire plant when using a systemic chemical.

Growers should be careful not to exceed the label recommendation of maleic hydrazide. Excessive residues on the cured leaf have in the past discouraged foreign buyers of burley tobacco. If rain occurs within 12 hours after spraying, reapplication is necessary. However, after 6 hours use a half rate only. Inspected plants daily for sucker regrowth. If suckers are green and growing, remove large suckers and re-spray.

Tobacco plants that have been growing under drought conditions absorb maleic hydrazide more slowly and, consequently, sucker control may be less effective than in a normal season. Also, poor sucker control may occur because of poor plant coverage if improper nozzles or less than 30 gallons of solution per acre are used. Applications made on bright sunny days increase the chance of chemical burn when the temperature is above 90oF.

Use of a contact chemical

The contact-type sucker control chemicals contain "fatty" alcohols (FA) as the active ingredient. Apply as a coarse spray so that it runs down the stalk and contacts the young sucker buds. With power equipment use a three-nozzle arrangement with TG3 and TG5 full cone tips or equivalent. Pressure should not exceed 20-25 psi. Direct the center nozzle (TG5) straight down and the side nozzles (TG3) toward the upper part of the plant. With a backpack or knapsack type sprayer, direct a coarse spray toward the upper end of the stalk. It is not necessary to cut off the spray between plants. To reduce leaf damage, keep the nozzles of either type of sprayer at least 12 inches above the upper leaves while spraying.

Two gallons of chemical in 50 gallons of total spray solution are sufficient for one acre of tobacco. Apply contact-type chemical immediately before or after topping or within 2 days after topping. Remove suckers longer than one inch at topping. Contact chemicals work quickly to kill suckers killing suckers within an hour if no rainfall occurs.

Precautions for using contact sucker control chemicals

Poor sucker control often occurs if plants are not in an upright position, because the chemical will not come in contact with all the sucker buds on a leaning or crooked plant. Straighten any leaning plants prior to application.

During prolonged periods of high temperature and humidity, contact chemicals can cause some loss of lower leaves because of stem rot. Higher-than-recommended rates increase the problem.

Do not mix contact sprays with insecticides for application.

Use of a local systemic

Two local systemic sucker control chemicals are currently available, Prime+ and Butralin. When applied alone application to the top of the plant is necessary. As they runs down the stalk and into each leaf axil systemic control occurs.

Prime+ should be applied when most tobacco plants are in the early flowering stage. That's important because the number and size of suckers should be small. If application is made too early, it may result in upper leaf distortion. Suckers more than one inch long must be removed at final topping.

For best results, this chemical should be hand applied to each individual plant. This can be accomplished by three different methods (dropline, backpack and jug). This chemical can also be applied with power equipment, using a course spray nozzle arrangement similar to that used for the contacts. However, sucker control may be less than that achieved by the hand method.

Dropline - This involves equipping the sprayer (trailer, tractor mounted, or hi-boy) with droplines for each row. About six to ten feet of pressure hose, equipped with a cutoff valve and a large volume nozzle is attached to each sprayer outlet. One person operates each dropline, following the sprayer down the row, treating plants that have reached the elongation bud stage.

Backpack - This method is similar to the dropline with regards to application methods. The backpack consists of a spray tank and a wand attachment with a nozzle body that can be adjusted or fitted with a course spray nozzle. The wand attachment allows the spray to be directed to top of each plant. Small acreage growers prefer this or the jug method of application.

Jug - This method involves adding the chemical to a gallon jug and pouring on about 1/2 ounce of the chemical per plant.

Rate - one gallon of Prime+ should be mixed in 49 gallons of water, regardless of the application method. An equivalent amount for the jug method is 2.5 ounces of Prime+ in one gallon of water. If a hand application method is used, 25 gallon of spray solution per acre should be used. With power equipment, a volume of 50 gal/acre is necessary. Due to the shorter growth habits of dark tobacco, when using power equipment the volume of solution can be reduced to 30 gal/acre.

Note - Sucker escapes may occur when using Prime+. MH escapes tend to grow slowly from leaf axils low on the plant, and remain concealed. Prime+ escapes, however, grow only from axils that did not receive adequate treatment, and will grow unchecked until removed. Correct application of Prime+ will result in only scattered escapes that are highly visible. Removing escapes within two weeks after application is recommended.

Handling Uneven Crops

Proper topping time is difficult to judge in an uneven crops. One option is to top only those plants that are ready and treat with a contact or Prime+ systemic sucker control chemical. Later, as the rest of the crop matures, the remainder of the plants should be topped and treated. If maleic hydrazide (MH) is used, it can be broadcast over the entire field.

A two stage topping program may not improve yield and quality enough to justify the extra cost. A better choice may be to top the entire crop as the good tobacco matures. Tobacco plants that are delayed in maturity should be bud topped to a 10 to 12 inch leaf. Many producers tend to let the good tobacco pass its peak trying to improve poor tobacco. Improvements in the poorer tobacco seldom are large enough to compensate for the loss to the good tobacco.

Timing Harvest Dates

Many producers still think that the longer the tobacco is left in the field, the larger the yield. While this is true within the first few weeks after topping, it continues only to a point. Early maturing varieties like KY 14 X L8 tend to reach this point at approximately 3 to 4 weeks after topping. Most other varieties need to be left 4 weeks, but some late maturing varieties like TN 86 and KY 8959 can stand for 5 weeks without much decline. By this time burley tobacco has had time to mature. Tobacco left for longer periods of time will start to decline and diseases that normally do not affect healthy tobacco may begin to damage the crop. Tests conducted to evaluate tobacco buyers preference for tobacco harvested at different stages after topping, revealed a greater acceptance for tobacco harvested at 3 to 4 weeks after topping. Tobacco left for 5 to 6 weeks was judged to be of poor quality and yields had drop.