GREENHOUSE PRODUCERS
OF TOBACCO TRANSPLANTS NEWSLETTER

By EMMETT S. SHOULARS, COUNTY EXTENSION DIRECTOR

We have seen many changes and improvements in structures, production and management practices for production of tobacco transplants in greenhouses. Growers have experimented with many ideas and research has addressed others. This newsletter is provided to assist you in planning for this plant season. Suggestions are provided as guidelines rather than absolute requirements.

Included is a diagram of a greenhouse that you may use to record bay location and dimensions. I have attempted to ease fertilizer calculations by combining constant values into a permanent record. You may utilize this to your benefit.

SANITATION

Tray sanitation is essential when using trays from previous crops. All soil and plant residue should be removed and trays washed.

Once trays have been washed with water to remove residual soil, methyl bromide fumigation is the most effective sanitation method for disease control other than TMV. Fumigate with methyl bromide at to 3 pounds per thousand cubic feet. Trays should be stacked so the fumigant gas will move throughout the entire stack. If trays are stacked higher than 5 feet air circulation with fans may be necessary.

Use of a 10% chlorine solution should be an additional sterilization technique if you suspect TMV infested plants were grown in trays.

At planting time, tray sanitation should receive additional consideration. Remember that disease organisms survive in the soil. Trays contacting soil in the field may be a source of disease problems in the greenhouse.

Mower sanitation is extremely important. After clipping, the deck should be removed, cleaned and washed thoroughly. It should then be sanitized with a 50% chlorine bleach solution.

You may consider a foot bath at entry points utilizing a 10% chlorine bleach solution to prevent introduction of disease organisms. Some individuals who enter may have contaminated soil from tobacco fields or other areas on footwear. Organisms that infect tobacco plants come from many sources. Sanitation is extremely important.

If disease problems begin to develop they should be addressed rapidly. Disease organisms in a greenhouse have optimum temperature and moisture conditions for rapid development. Most important in disease prevention are sanitation, adequate ventilation and air movement to control humidity.

Ventilation is necessary to avoid high daytime temperatures on sunny days and to reduce humidity. When greenhouse temperature reaches 90 degrees F, additional ventilation will be needed to prevent higher temperatures and possible plant injury.

SEEDING

That the following sequence is beneficial for filling trays to ensure that each cell will wick resulting in less dry cells.

After soil delivery, check moisture to determine if addition of water is necessary. Add approximately 1 gal. of water per bag and reclose bag 3 - 4 days prior to seeding, if needed to improve working condition of soil. Amount is dependent on soil moisture content. This will improve tray filling by keeping fine soil from running out the bottom. Very fine soils are more likely to fall out of the cells if dry. Dipping trays or spraying with water may be helpful.
Fill tray with soil evenly and be sure there are no air pockets.
Randomly check bottom of some trays to be sure cells are filled completely.
Use dibble board to compress soil. Repeated dibbling may increase aerial roots due to increased water absorption. Aerial roots have been observed in most greenhouses. Although there was much concern it generally involves a very small percentage of seedlings. Over compaction of soil to assure wicking may result in soil packed so tightly that it becomes completely saturated with water. Aerial roots are the plants response to excess water in the soil medium with an attempt to maintain oxygen availability. Avoid over compaction when filling trays.
Seed trays. Ensure that only one seed is placed in each cell.
Place trays in bay with minimal handling.
Evaluate wicking in 20 to 30 minutes. After this time very few additional cells will wick. If less than 99% you need to alter soil filling process.
Wicking is more difficult with new trays than with used trays. When seeding trays for the first time, trays may need to be wet before filling and soil moisture content should be higher than for old trays.
If trays do not wick adequately overhead application of water with the spray boom may be beneficial. Good results can be obtained by placing a board across the trays and pressing down from both ends until cells wick. With either method, avoid moving the seed or pushing parts of trays underwater.

Approximately 10 days following seeding you can make a plant count to determine germination. Plants with aerial roots should not be counted. Cells containing two or more plants should not be counted. These plants will be too small to plant. Seed which have not germinated and plants that appear smaller than others should not be counted. This will help you to evaluate the success of your operation at this point in time and estimate total plant production.

Inadequate ventilation will result in moisture condensation causing dripping. This can wash soil from cells and destroy seedlings. Monitoring the house frequently is essential. When condensation occurs more ventilation is needed. Automatic side curtain controls for ventilation operate on temperature control. You may need to adjust thermostats in order to avoid excessive humidity. It is extremely difficult to remove humidity on cloudy, rainy days. The house must be monitored throughout the day. Select seeding date based on weather predictions for the 5 day forecast. Avoid seeding on cloudy, rainy, high humidity days and when these conditions will occur immediately after seeding.

Drop curtains in the morning to bring in fresh air after heaters run through the night. Combustion gasses that may be associated with fasciation (twin buds) are removed. Thermostats should be set so that heaters will not come on when curtains are open.
Installing exhaust fans above end doors to assist in removing hot air during sunny periods is beneficial. Thermostats will have to be set for conditions within the individual house.
Circulation fans help to evenly distribute heat and reduce condensation. Fans should run constantly. They may be beneficial in reducing disease development and are highly recommended.
Generally over ventilation causes less problems than under ventilation.

TEMPERATURE

Optimum germination and growth occur at approximately 72oF at tray level. After germination is complete, a minimum night temperature of 55 to 60oF is adequate at tray level. Lower temperatures may be considered as plants get larger, but cold injury symptoms could be observed. Certain varieties may be more sensitive than others. Cold injury symptoms may be a result of the wide swings in temperature from day to night or increased sensitivity of greenhouse plants.

Cold injury shows some or all of these symptoms:

Yellowing of the bud leaf

Yellowing of some of the larger leaves

Upward cupping of outer edge of leaf

Thickening of some leaves

Elongation of some leaves

A few scattered plants showing cold injury symptoms are seen in most greenhouses. A large number of plants with this appearance would indicate that growth rate may be slowed. Raising the night time minimum temperature a few degrees should reduce this occurrence. It will be best to keep the plants actively growing.

Trays in 2 to 3 rows near side curtains will have smaller plants than in the center of house. If you prefer more uniformity, these may be rotated with larger plants near the walk. They produce good plants if left in place but may need to be left in the greenhouse for an extra week.

New greenhouses generally have few insect problems early. Older houses may have insect populations at this time. Crickets and slugs are problems that may occur prior to seeding. Control requires sanitation and outside perimeter treatments to be effective. Orthene 75 may be applied inside the house prior to placing plastic in waterbeds. The rate is 1 Tablespoon per 3 gallons of water per 1000 square feet.

Mice have been a problem in most older houses. They nest in end walls and between boards. They eat seed coating and young plants similar to cricket damage. Utilize rodent control practices through the winter, prior to seeding and during early growth. Mice and rats are difficult to detect. Plants generally begin to disappear during germination at ends of the house and new sidewalls.

Very few agricultural chemicals have labels for greenhouse use. Labels or Extension staff should be consulted if you have questions about use of products. Additional labels may be approved later.

Disease control also requires good management practices and sanitation. Take steps to avoid contamination from outside soil and tobacco products being used by employees. Tobacco Mosaic Virus (TMV)can be devastating because it is easily spread in greenhouses. Several diseases have occurred in greenhouses. Monitor plants daily to observe any growth problems that occur. Most diseases begin as very small spots of wilted or weak plants. Diseases spread rapidly. Contact the Extension Office for identification and updated control recommendations.

Greenhouses should have a good spray system mounted on the boom. You should be able to change nozzles to apply pesticides with the correct volume of water or apply water to improve wicking if necessary.

FERTILIZATION - OVERHEAD WATERING

After seeds have germinated -- use 50 ppm of either 20-10-20 or 20-20-20 water soluble fertilizer in irrigation water 2 - 3 times per day for 2 weeks. The number of waterings per day will depend on:
1. Soil mix
2. Ventilation
3. Heat
4. Sunshine
Increase fertilizer to 100 ppm for the remainder of the growing season. This should be sufficient to finish plants.
One day per week flush house with clear water and 50 ppm of Epsom salts.
Do not let soil dry out. It is extremely difficult to rewet dry soil.

FERTILIZATION - FLOAT GREENHOUSES

Researchers and growers have experimented with numerous fertilization programs including rates and frequency of application. Many different programs are successful. A two step simplified fertilization program that works well is:

Apply 100 - 150 ppm N using a complete fertilizer at or within 7 days after seeding.
Apply second fertilization of 100 ppm N four to five weeks later. Ammonium nitrate may be used to meet this nitrogen requirement.

Select a high quality fertilizer material that is formulated for soil-less media. General purpose soluble fertilizers are used in soil and may not contain adequate micronutrients. Taking a water sample is suggested to determine if micronutrients will be needed. Boron deficiency has been identified in the Piedmont. Boron deficiency which causes bud distortion and death may occur when water sampling indicates no boron content. If an analysis indicates that water contains little or no boron, use a fertilizer containing a trace level of this element. If a fertilizer with boron is not used, adding no more than 0.25 ounce of borax or 0.125 ounce of Solubor per 100 gallons of nutrient solution is sufficient to prevent a deficiency. Affected plants are stunted, yellow, and have small, brown root systems. Their leaves are often cupped downward. High bicarbonates have been detected in some water samples. Neutralization of the alkalinity is accomplished with addition of battery acid to the water to neutralize some of the bicarbonate. This should only be done with recommendation of NCDA solution analysis report.

When fertilizer is added to bays you must assure thorough mixing. If injectors are used, be sure they are calibrated properly. When adding fertilizer to each bay individually, dissolve fertilizer completely before pouring into bay and then add additional water to bay at the same point with waterhose. Allow to run for several minutes or utilize this opportunity to raise water to desired level.

The recommended level of fertility should be sufficient to grow plants to within a couple of weeks of transplanting. At that time, soluble salts meters may be used to check N concentrations and adjustments may be made. I have a meter and can check soluble salts when you have questions or a problem such as a leaking bay. If you have concerns about additional fertilizer needs please contact me.

Water depths should remain constant as plants are growing. As water level drops due to plant use and evaporation, nutrient content increases and the potential for plant injury develops. Rapid evaporation immediately after seeding may result in deposition of fertilizer salts in cells. Irregularities in growth (small vs. larger plants) within trays or areas of a bay may indicate fertilizer salts injury. Growth differences may be observed within a few days after germination. Samples of media and testing with soluble salts meters is essential for accurate determination. Soluble salts may be leached from the cells with high volumes of overhead watering.

To aid in maintaining uniform water level from one end of house to the other, you may consider installing water lines for each side of house in the walkway with tubes leading into each bay. This will act as a siphon to equalize water levels. Adding equal amounts of fertilizer and water to each bay will maintain uniform fertility.

You must determine water capacity in a bay to develop a fertilization program. This can be done with the following formula and example.

The conversion table of inches to decimal equivalents in feet will be useful.

          1/4" = .02 ft.           2" = .166 ft.
          1/2" = .041 ft.               3" = .25 ft.
          3/4" = .062 ft.               4" = .333 ft.
          1"   = .083 ft.               5" = .416 ft.

          Gal.water = L (ft)  X  W (ft)  X  D (ft)  X  7.48 gal/ft3

EXAMPLE:  L = 50 ft   W = 13 1/2 ft   D = 4"

             gal = 50  X  13.5  X  .333  X  7.48

             gal =  1681

The calculations for adding fertilizer require determination of parts 


per million.  In tobacco greenhouses we calculate the ppm of nitrogen to be added.  Most growers are using 20-10-20
so adequate levels of P and K will be supplied.

Continuing the above example calculation of fertilizer needed to get a concentration of 150 ppm is done with the
formula:

          ounces of fertilizer                ppm  desired     
       per 100 gal. water   =          % of nutrient X 0.75

       ounces/100 gal =           150         =       150   
                               20  X 0.75              15

       ounces/100 gal =   10

The bay held 1681 gal or 16.81 one hundred gallon units

       pounds of fertilizer  =         10   oz   X  16.81   
       to add to the bay                16 oz/pound

       lbs. fertilizer = 10.5

Attached is a chart on which you may draw in the bays in your greenhouse and indicate the measurements. These will be necessary to determine water content. You can then multiply L x W x 7.48 to determine a CONSTANT (C) value. This value will never change in that bay. You can then simply multiply this CONSTANT (C) value times the water depth to determine gallons of water in the bay. If all bays are the same size the (C) will be the same. Using this will reduce calculations needed to determine fertilizer applications and reduce the chance of error.

Once the number of gallons is determined, the following chart may be used to determine fertilization rates when using a fertilizer with 20% N. Select the desired ppm N and its equivalent ounces of fertilizer per 100 gal. Multiply oz. of fertilizer by the number of 100 gal. units in the bay.

        ppm N               ounces compete fert.containing 20% N
         50                   3.3                  per 100 gal.
         75                   5.0 
        100                  6.66
        125                  8.33
        150                  10.0
        175                  11.66
        200                  13.33

Ammonium nitrate may be used to provide needed nitrogen after initial complete fertilizer is applied. The following chart gives the rate of Ammonium Nitrate to use per 100 gallons of water. You should test water with bays full to determine N ppm before making additions. Total N ppm should not exceed 200 ppm.

                                      
     ppm N                              Ounces Ammonium Nitrate
  supplied in water                     per 100 gallons water
     1 oz                               25
     2 oz                               50
     4 oz                               100

CLIPPING

Clipping is essential to greenhouse production. It promotes uniformity, hardening of seedlings and stem diameter. The number of clippings depends on growth, uniformity, cell size of the tray and how long plants must remain in the house. In previous years, some growers have clipped as many as 10 times. Clipping should begin when the largest plants are 3 inches to the bud. Small cell size, high density, will require earlier clipping than large cell size, low density. Irregular growth will require that clipping begin earlier. Excessive early clipping reduces the growth rate of plants. Clipping closely when plants are small is advised only when germination and early growth are extremely erratic. In this case it may be necessary to achieve uniformity. It is not advisable to clip plants severely at any stage of growth. Several light clippings are preferred over one close clipping. If weather conditions delay planting, close clippings may be utilized to held plants back. We are more concerned about growing the plants early rather than holding them back. Be sure to avoid long, leggy plants. They are difficult to plant and may suffer stem injury once in the field.

Clippings should be bagged and disposed of away from the greenhouse area. Disease organisms may survive on the debris increasing disease pressure. Clipping practices should prevent leaf tissue from dropping into trays of plants. Most diseases begin on this decaying material. Avoid early seeding dates that increase the number of times plants must be clipped.

You may consider different clipping practices and fertilization on the two sides of the greenhouse to extend your planting season. Relying on clipping once plants are large enough to go to the field may not prevent excess height.

The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned.

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This document was written by Scott Shoulars, County Extension Director
This document prepared for WWW by Donna Fulp, County Extension Secretary on 11/24/97.
Last Updated 11/24/97

GREENHOUSE PRODUCERS OF TOBACCO TRANSPLANTS NEWSLETTER