For flue-cured grower Ronnie Betts of Duncan, N.C., the key to getting a good stand of tobacco is growing a good plant. And he thinks a relatively tall plant works best with modern transplanters.
“I like a plant that is at least 5.5 inches from the top of the root to the bud,” he says. “You need enough height to set the plants deep enough. But much longer, and it may lie over once you set them out.”
A properly clipped plant is essential for carousel transplanters, agrees North Carolina State University Extension Tobacco Specialist Loren Fisher. “Uniform stem lengths are needed to transplant seedlings at the proper depth, and excessive foliage disturbs the timing mechanism.”
But Virginia Tech Extension Tobacco Specialist David Reed suggests a bit shorter plant than Betts recommends.
“Stems that are 4 to 5 inches in the field are about right,” he says. “You don't want a long plant with a long stem that you may not get in the ground. It may sucker out in the bottom of the plant and just lay on the surface.”
Betts and his brother Ricky believe in taking an aggressive approach to clipping.
“We mow ours every other day and take about three fourths of an inch of new growth each pass,” he says. “But you have to stay at least a half inch above the bud. You have to be real careful when you are doing this.”
The Extension specialists take a little more conservative approach.
“Current recommendations are to begin clipping at three- to five-day intervals when total plant height is 2 to 2.5 inches above the tray with the blade height set at 1 to 1.5 inches above the bud,” says Fisher. “This procedure provides the best balance of uniformity, stem length and disease management.”
Reed says to clip on a three-day interval between the first three clipping dates and every five days thereafter. “You may well find it necessary to clip in two passes to remove height and also to clip clean,” he says.
The key to effective clipping of float plants is to make a clean cut and remove the clipped material from the area, says University of Kentucky Extension Tobacco Specialist Bob Pearce.
“To accomplish this, use a sharp blade and adjust the mower's speed so the clipped material is lifted off the plants and deposited in the bagger,” he says. “A high blade speed will result in the material being ground to a pulp and being deposited back on the trays, increasing the likelihood for diseases.”
A dull blade, on the other hand, may tear the leaf, and that may not promote proper healing.
“A relatively low blade speed with a sharp blade works best,” Pearce says.
You don't want too much of a vacuum effect. “Although some vacuum is necessary to push clipped leaves into a leaf catcher, a high vacuum may pull plants from the trays or suck the trays up into the blade,” says Pearce. “Dispose of clippings in an area well away from the greenhouse to prevent disease development that could spread to healthy plants in the float bed.”
The first time you clip burley plants, you should try to remove one half to 1 inch of leaf material, says Pearce. “The first clipping promotes uniformity,” he says. “Smaller plants may not be clipped the first time but will benefit from more sunlight and less competition from plants that were taller prior to clipping.”
After the first clipping, burley plants should be clipped every five to seven days depending on growth rate, says Pearce. “At each clipping, remove no more than one half to 1 inch of leaf material. Three to five clippings may be necessary to achieve the best plant quality. Seldom are more than five clippings necessary,” he says.
Also, collect plant clippings to reduce the likelihood that disease will develop and spread throughout the entire greenhouse, says Reed. “The mower should be thoroughly cleaned and sanitized with a 50-percent chlorine bleach solution following each use.”
Too much clipping can cost you. Fisher notes that many North Carolina growers clip 15 to 20 times, largely because they seed the greenhouse too early.
“Early seeding increases heating costs as well as the potential for collar rot,” he says. “And if you clip too early or too close to the bud, you can reduce stem length, increase stem rot, and slow plant growth in the field.”
“Hard” clipping of burley plants should be avoided unless plant growth needs to be controlled, adds Pearce. “Plants should never be clipped so severely that buds are damaged, since transplants with buds removed may yield much less than non-injured plants.”
When done properly, Pearce says, clipping actually aids in disease control in the greenhouse.
“It opens up the plant canopy to allow for greater light penetration and improved air circulation around the plants,” he says. “The mower and surrounding frame should be thoroughly cleaned after each use and sprayed with a disinfecting solution of 10-percent bleach or a commercial greenhouse disinfectant. If left on metal surfaces, bleach will promote rust, so rinse all surfaces after 10 minutes of contact time.”
Gasoline-powered reel-type mowers have been used successfully for clipping plants, says Pearce, and they tend to make a clean cut, producing large pieces of intact leaf and depositing them in a catcher with little or no grinding. However, rotary mowers may be easier to adjust and maintain.