Example: 16 ft x 5.5 ft x 4 in x 7.48 = 217 gal

2. The amount of fertilizer required per 100 gal of water is calculated by:

desired nutrient concentration (ppm) x 1.33
nutrient content of fertilizer (%)

Example: 150 ppm N x 1.33 = 10 oz per 100 gal

Table 1. Amount of selected fertilizer grades to produce fertilizer solutions with 50 to 200 ppm nitrogen.

	ounces of fertilizer per 100 gals of water at various nitrogen (N) concentrations (ppm)
Fertilizer analysis	50	75	100	125	150	200
20-10-20 or 20-9-20	3.3	5.0	6.7	8.3	10.0	13.3
17-5-24	3.9	5.9	7.8	9.8	11.7	15.6
17-5-24 and 15-0-15a	2.6 and 1.5	3.9 and 2.2	5.2 and 2.9	6.6 and 3.7	7.8 and 4.4	10.5 and 5.9
16-4-16 or 16-5-16	4.2	6.2	8.3	10.4	12.5	16.6
15-5-15 or 15-4-15	4.3	6.7	8.9	11.1	13.3	17.7
aFertilization program with 2 parts 17-5-24 and 1 part 15-0-15.

Proper Tray Filling and Seeding are essential to produce a high percentage of usable plants. The media used for float transplant production is a specially formulated material and can not be satisfactory substituted with common potting media used with house plants. Greenhouse tobacco mixes should be available from most farm supply dealers. When filling trays, media should have sufficient moisture to properly pack into the cells. If the media needs additional moisture, water should be added to the bags the day before trays are to be filled.

When filling trays by hand, distribute the potting mix in a systematic manner to fill all cells with the same amount of mix. Dry cells occur when media does not fill the entire cell and thus fails to wick properly. Seed in dry cells do not germinate and thus a potential transplant is lost. A second problem related to tray filling is the occurrence of spiral root plants. This condition occurs when the root of a germinating seed does not penetrate into the media. Such plants will eventually die and thus a potential transplant is lost. The cause of spiral root plants is not completely understood; however, it does appear to be related to inadequate media aeration (too little air/too much water). Media must not be packed too tightly into trays or excessively moistened. If float trays are watered over-the-top to help dissolve seed coatings, water should be applied as a fine mist. Large droplets can result in excessive packing and waterlogging of the media.

Tray selection will influence both the productivity and management of a greenhouse. The different Styrofoam float trays used for tobacco production are the same size but differ in the number of cells or plants per tray (see Table 2). The advantage of high cell count trays is the increased productivity of a given size greenhouse. For example, 44 percent more transplants could be grown using 288 cell floats instead of 200 cell floats. However, the level of management is greater with the higher density float trays. Both root volume and stem diameter decrease with increasing cell number; and therefore, greater clipping frequency will be required to ensure adequate stem size. In addition, the increased crowding of the seedlings necessitates more critical ventilation and moisture reduction within the greenhouse to prevent environmental conditions that favor the development of disease.

Table 2. Float trays commonly used for greenhouse tobacco production.

Cells per tray	Vol. per cell (cc)	Plants per sq. ft.
200	27.0	80
242	23.5	97
253	16.0	101
288	17.0	115
338	8.6-11.2	135
392	13.6	157

Research conducted in Virginia to evaluate the impact of float cell number on transplant size and growth in the field. Stem diameter and plant size of 200 and 288 cell transplants were similar. Transplants from 338 cell trays, and to a greater extent 392's, were significantly smaller than those from 288 or fewer cell trays. However, there were no differences in plant stand, early-season growth, and yield of plants from any of the float trays tested.

The biggest difference between the float cell numbers is the cost per transplant. The larger transplants from a 200 cell float cost more to produce since fewer can be grown per square foot of greenhouse. For tobacco growers in Virginia, the 253 or 288 cell floats would be a good compromise between transplant size and transplant cost. This is especially important with outdoor float bed growers who must balance transplant number needed against the ability to adequately heat the float beds.

Attention to the seeding of trays will result in a greater number of usable transplants. Tray cells not seeded or double seeded will reduce the number of transplants. Proper dibbling of trays (creating shallow depressions in each cell) will provide better seed/media contact and position the seed in the center of the cells. The date that a greenhouse is seeded has a significant impact upon the management of a greenhouse. Seeding too early increases heating costs, lengthens the exposure of plants to possible pest problems, and requires excessive clipping. Sixty to 65 days is a conservative estimate of the time needed to allow for growing plants from seeding to transplanting time in a direct-seeded outdoor float bed.

Tobacco Transplant Production in Outdoor Float Beds
Outdoor float beds are a low cost method of greenhouse tobacco transplant production for limited acreage. Seedlings in outdoor float beds may be started by two different methods. The first is direct-seeding, as in a conventional transplant greenhouse. The alternative is to produce transplants using a seedling transfer production method.

Transfer beds are used only to grow plants off from a small seedling stage to transplant size. Seeds are not actually germinated in the outdoor transfer float bed. As a result, the heating requirement is greatly reduced since frost protection is the primary concern. The disadvantage of transfer beds is the increased labor necessary for hand transfer of the small seedlings to the float trays. The plug-and-transfer method was the original method of producing burley transplants using the float system. Commercially-grown "miniplugs" or small seedlings are purchased in special trays and transferred by hand to conventional float trays. Seedlings are grown to transplant size in either an outdoor float bed or greenhouse. Although miniplugs represent an additional expense, they do reduce the risk and management associated with other float transplant production methods. In the seed-and-transfer method seedlings are started from conventional, uncoated seed and transferred to float trays in outdoor beds. Detailed directions for seed-and-transfer tobacco transplant production may be found later in this section of the production guide.

Float Bed Construction
Outdoor float beds may be designed and constructed in many different ways. Individual growers should consider the materials available and the desired expense when considering how to construct float beds. Factors to consider include: 1) adequate strength of the top, 2) providing sufficient heating, and 3) ease of access for observation and management of seedlings. Outdoor float beds evaluated at the Southern Piedmont Center in 1993 and 1994 have utilized a narrow design with a separate frame for the top that can be completely removed from the bed. Such a design allowed for excellent access to the seedlings, complete ventilation of the float bed, and clipping of the seedlings with a tractor-mounted bush-hog.

The size of the float bed(s) to be constructed will be determined by the required number of transplants, the ability to provide adequate heating, and the float tray cell size to be used. Float trays are approximately 13.5 in. wide and 26.5 in. long and vary in the number and size of cells in which the seedlings grow. Comparative information on the different float trays available is presented later in this section of the production guide.

The frame of the float bed should be sized to hold the desired number of trays and have approximately 2 in. of additional space along the length and width of the bed to allow ease of removal of float trays. Larger amounts of exposed water will encourage excessive algae growth.

One example of an outdoor float bed to grow transplants for the average-sized burley tobacco producer would be a 40 tray float bay. Trays in the bay could be arranged 5 wide (side-to-side) and 8 trays long (end-to-end). The inside dimensions of the float bay frame (2 x 6 in lumber) would be:

length = 8 trays x 26.5 in. + 2 in. = 17 ft. 10 in.
width = 5 trays x 26.5 in. + 2 in. = 5 ft. 10 in.

The number of transplants produced from this 40-tray float bed will be influenced by the float tray cell number and the percentage of usable transplants produced from each (dependent on management).

	Number of transplants from 40 trays with
Float tray cell number	75% usable	90% usable
200	6000	7200
253	7590	9108
288	8640	10,368
338	10,140	12,168
392	11,760	14,112

If increased transplant number is needed, larger beds may be constructed. However, growers are reminded to consider the heating requirement, necessary structure strength of the top, and ease of management with larger float bed sizes.

The length of the bed can be made from 1 or more lengths of 2 x 6 treated lumber and joined securely. Short wooden stakes driven into the ground along the length of the bed will keep the frame from bowing under the weight of the water contained inside. The cover over the float bed may be constructed in one of many different ways. Factors to consider include:

• The top must have adequate strength to support any accumulation of rain or snow. Strength is dependent on construction materials used and spacing of the bows over the float bay.
• The height of the top over the trays should be sufficient to shed water. However, if too great, heating will be made more difficult.
• A top that can be easily removed and replaced will improve management. A completely removable top will allow for better observation of plants, ease of clipping, and allow for better ventilation.

The bed frame should be lined with a single layer of 6 mil black plastic to hold water in the float bay. The ground under the plastic should be smoothed and may be covered with a thin layer of sand or rock dust to reduce the likelihood of sharp objects puncturing the plastic liner. Any leaks that do occur should be repaired. Float beds should be located on a site receiving full sun and near electricity, if necessary. The site should be leveled to provide uniform depth of water throughout the float bays. Sand or rock dust may be used for leveling and will reduce drainage problems and muddy areas around the bays.

Suggested Sizes of Outdoor Float Beds
The following are suggested dimensions for the style of float beds evaluated at the Southwest Virginia and Southern Piedmont ARECs. These beds consisted of a 2 x 6 frame for the water bed and a 2 x 4 frame (turned up on the 2 in. side) around the water bed to attach cover support bows made from 3/4 in. flexible water pipe. The 2 x 4 cover frame can be completely removed from the float bed to provide ventilation and allow for clipping.

			Inside Dimension
Tray Number			2 x 6 in. bed frame		2 x 4 in. frame for cover
Width	Length	Total	L1	W1	L2	W2
3	6	18	13' 5"	3' 7"	13' 10"	4' 6"
3	8	24	17' 10"	3' 7"	18' 3"	4' 6"
3	10	30	22' 3"	3' 7"	22' 8"	4' 6"
4	6	24	13' 5"	4' 8"	13' 10"	5' 1"
4	8	32	17' 10"	4' 8"	18' 3"	5' 1"
4	10	40	22' 3"	4' 8"	22' 8"	5' 1"
5	6	30	13' 5"	5' 10"	13' 10"	6' 3"
5	8	40	17' 10"	5' 10"	18' 3"	6' 3"
5	10	50	22' 3"	5' 10"	22' 8"	6' 3"
6a	10	60	22' 3"	6" 11"	22' 8"	7 ' 4"
6a	14	84	31' 1"	6" 11"	31' 6"	7 ' 4"
6a	18	108	39' 11"	6" 11"	40' 4"	7 ' 4"
6a	22	132	48' 9"	6" 11"	49' 2"	7 ' 4"

^aThe size of a removable top constructed with a 2 x 4 frame may be too large with float beds wider than 8 feet or longer than 15 or 20 ft.

Bows supporting the cover can be made from 1/2 or 3/4 in. plastic PVC pipe. Space bows 18 to 24 in. apart. The length of the bows should be 90 in. for a float bed 4 trays wide and approximately 104 in. for a bed 5 trays wide.

Constructing float beds wider than 6 trays or longer than 15 or 20 feet will make a removable top difficult to lift. In this case, other provisions must be made to provide adequate ventilation and access to the float trays.

Heating of Outdoor Float Beds
Supplemental heat will be necessary for reliable production of transplants in outdoor float beds. Transfer beds may require limited heating for frost protection. Heat lamps strung above the plants for the length of the float bay (100 watts per 100 sq. ft.) or water bed heaters should provide adequate frost protection. Direct-seeded beds require more extensive heating to obtain satisfactory germination. The low cost, temporary nature of outdoor float beds limits the available options for heating. Early research with outdoor float beds evaluated the use of ceramic heaters for direct-seeded outdoor float beds. However, the use of such heaters is discouraged due to the potential electrical hazard associated with outdoor float beds. The high electrical demand of ceramic heaters coupled with safety considerations limit their usefulness in heating outdoor float beds. Each ceramic heater requires a separate 20 amp circuit with a ground fault interrupt.

Water bed heaters (heat mat placed under the bed liner) have successfully been used for heating direct-seeded float beds. One heater per 20 trays should be sufficient if other necessary procedures are followed. Thermostats should be set at 80°F. Empty trays (one per water bed heater) should be placed in the bed to allow heat to move from the water to the air above the trays.

Heat loss, and therefore, the heating requirement can be significantly reduced by covering beds with solid plastic to reduce radiational heat loss occurring at night. Such covers should be provided when low temperatures are predicted to fall to 35°F or below.

Growers must exercise extreme caution and follow all safety rules pertaining to electrical wiring and the use of electrical equipment in the outdoor environment and near water.

Covers for Outdoor Float Beds
Clear, solid plastic should not be used as a cover material for outdoor float beds. High temperatures may buildup very rapidly under solid plastic and kill young seedlings. The typical outdoor float bed does not have sufficient ventilation to prevent the buildup of excessive heat. Fabric plant bed covers, such as Reemay and Typar, are better suited for float beds. Although not essential, two layers of Reemay or a heavier weight cotton cover may be used to further insulate the beds during cold weather, particularly during germination of the seed. Vispore, a plant bed cover material made by Tredegar Industries, is a perforated plastic cover that has been evaluated on outdoor float beds at the Southwest Virginia and Southern Piedmont ARECs. The very small holes in this material reduce the buildup of excessive heat, but are so small that rainfall cannot pass through the cover onto the plants. It is recommended that the heavier grade (2.5 mil) of this cover be used for float beds, and that the cover should be turned with the rough side up (to better shed water).

Resent research has shown the use of a 50% white shade plastic to be a very effective cover for outdoor float beds. Growers should be sure that the shade plastic is actually 50%. If the covering is higher percent shade, seedlings will become spindly for lack of sunlight., however, less shade would allow too much sunlight resulting in temperatures high enough to damage or kill seedlings.

An on-farm study showed fewer incidences of spiral root seedlings when produced using the 50% shade plastic with the outdoor float bed than in a traditional greenhouse. This was probably a result of higher humidity in the float bed and less drying of the seed and pellet.

Procedures for Seed and Transfer Transplant Production
Transplant production with the seed-and-transfer method begins with the sowing of uncoated seed in small pans or trays, and later hand-transfer of the young, bare-rooted seedlings to float trays used for greenhouse production. Specific steps in the seed-and-transfer procedure include:

1. Seeding of germination trays
   • Plastic nursery flats available from most garden stores make excellent germination trays. The most common size is 22 x 11 in. and approximately 2 in. deep. The use of double trays, one with small holes in the bottom and placed into a solid bottom tray, will enable watering of the germination trays from the bottom.
   • Fill germination trays with soilless greenhouse mix that will be later used for the float trays. Do not pack the potting mix in trays; allow to settle into place. Overpacking will result in waterlogging of the media and cause poor seedling growth.
   • Germination trays may be seeded by what is commonly called the "salt shaker" method:
     • Mix seed with a carrier for even distribution of seed. Two tablespoons of clean sand (white play sand) and tobacco seed measured from two .22 caliber long rifle shell casings should be mixed thoroughly for each germination tray.
     • Distribute the seed/sand mixture using a clean salt shaker. Greater uniformity is possible if more than one pass is made over each tray.

2. Fertilization and watering
   • Watering from the bottom rather than overtop is most desirable.
   • The potting mix may be initially wetted prior to seeding or immediately after trays are seeded.
   • The initial wetting should be with fertilized water, using 1 teaspoon of a water soluble 20% nitrogen fertilizer (20-20-20 or preferably 20-10-20). This amount of fertilizer should be sufficient to grow seedlings to the transfer size.
   • Check trays daily for watering; keep approximately 1/2 in. of water in the bottom tray.

3. Growing environment
   • Germination trays may be placed in a heated (70oF) area of a house receiving indirect sunlight throughout the day. More attention is necessary if placed in direct sunlight. High temperatures that can kill young seedlings may occur if trays are covered with plastic and placed in full sun.
   • If fluorescent lights are used, place close together and directly above the trays (12 to 18 in.). Provide at least 14 to 16 hours of light each day (continuous light is acceptable). Trays placed under artificial lights may be initially covered with clear plastic to provide increased humidity for the first 3 to 4 days. Seedlings grown under artificial lighting will require hardening-off. Trays should be moved to outside shade for 2 to 3 days for hardening before transfer of seedlings to outdoor float beds.
   • Trays may also be placed in a heated greenhouse or heated cold frames. Special attention is necessary to provide adequate ventilation to prevent excessively high temperatures in small, heated, enclosed environments receiving direct sunlight.

4. Timing and number of germination trays
   • Seedlings will be ready for transfer 3 to 4 weeks after seeding (1 to 1 1/2 in. tall).
   • Each germination tray should produce 1200 to 1500 seedlings.
   • Allow an additional 4 to 5 weeks after transfer for seedlings to grow to transplant size in the outdoor float bed.

Return to Table of Contents

Disease Control For Burley Tobacco

Good disease control results from accurate diagnosis of disease problems, careful consideration of disease severity in each field, and prudent use of disease control practices. Crop rotation, early root destruction, and resistant varieties should always be used in conjunction with disease control chemicals because consistent disease control depends on the use of several control practices together.

ACCURATE DIAGNOSES OF DISEASE PROBLEMS is the first step in controlling burley tobacco diseases. Note any signs of disease during the growing season. Contact your Cooperative Extension agent when you believe that a significant problem may be developing. Plant and soil samples can be taken and analyzed to identify the cause of the problem. Don't forget to record what the problem was determined to be, where and when it occurred, and how bad it eventually became, so that you can plan appropriate control practices for the future.

CROP ROTATION is particularly effective in helping to control tobacco diseases and also provides many agronomic benefits. Length of rotation (the longer the better) and types of alternate crops are among the most important rotation considerations. Table 1 lists some possible rotation crops:

Table 1. Suggested Rotation Crops for Tobacco Disease Control

Disease	Suggested Rotation Crop
BLACK SHANK	Any alternate crop may be used
ROOT-KNOT NEMATODE	Small Grains, Fescue, Sudan Grass
TOBACCO MOSAIC	Most crops other than tomato and pepper
BLACK ROOT ROT	Small Grains, Fescue, Corn, Most non-leguminous plants.

EARLY DESTRUCTION OF ROOTS also reduces overwintering populations of nematodes and disease-causing organisms, as well as many insects, grasses, and weeds. The earlier and more complete the destruction of tobacco debris, the better the disease control. Always remember that the objective of early root destruction is to pull the roots out of the ground, dry them out, break them up, and get them decayed as soon as possible. Table 2 lists the steps involved in this important tobacco disease control practice:

Table 2. Steps in Early Stalk and Root Destruction

1. Plow or disc-out stubble as soon after harvest as possible. Be sure to pull roots completely out of the soil.
2. Re-disc the field 2 weeks after the first operation.
3. Plant a cover crop when root systems are completely dried-out and dead.

DISEASE-RESISTANT VARIETIES may be the most cost-effective way to control disease. However, varieties resistant to black root rot and black shank are not immune to these diseases. Significant losses can still occur under heavy disease pressure. Crop rotation and early root destruction should be used along with resistance. Pesticide use may be necessary in fields with a history of extremely severe black shank.

DISEASE CONTROL IN TOBACCO GREENHOUSES

Disease causing organisms can enter a greenhouse in soil or plant debris. Entrances should be covered with asphalt, concrete, gravel, or rock dust, and footwear should be cleaned or disinfected before entering a greenhouse. New float bay liners should be used each year and should be free of soil and plant debris. Greenhouse equipment should also be sanitized periodically. A 1:10 solution of household bleach and water is sufficient for these purposes, as are most disinfectants.

If tobacco mosaic (TMV) may have occurred in the previous year, greenhouse surfaces that may come in contact with plants should be disinfected. Such surfaces should include side-curtains, center walkways, and the 2x6 boards that form the float bays. However, there is no need to spray the purline supports or the plastic covers over the greenhouse. Relatively new float trays that may have been used when TMV may have been present should be washed and cleaned thoroughly before being fumigated. Old trays should be discarded and replaced with new trays. Mosaic has a number of weed hosts (horsenettle, ground cherry) which should be removed from the vicinity of tobacco greenhouses.

Float trays should be cleaned and then fumigated with methyl bromide or aerated steam (140°F to 175°F for 30 minutes) to minimize Rhizoctonia damping-off and sore shin. Dry trays should be loosely stacked no more than 5 ft high and completely enclosed in plastic. Three pounds of methyl bromide will fumigate 1,000 cubic feet (1,500 trays). Trays should be fumigated 24 to 48 hours, then aerated for at least 48 hours before use. Be sure to read the label for space fumigation and follow it exactly.

Do not fill float bays with water from surface water sources like streams or ponds. Water from these sources may be contaminated by soil run-off from fields infested with black shank or Granville wilt. Don't move water from one bay to another to reduce potential spread of water-borne pathogens. Be careful to avoid introducing disinfestants into water intended for plant uptake.

To avoid spreading tobacco mosaic or TMV, mower blades and decks should be sanitized with a 1:1 bleach: water solution between greenhouses and after each clipping. Plant debris left on trays after clipping is one of the primary causes of collar rot problems. High vacuum mowers should be used to clip tobacco seedlings. Clippings, unused plants, and used media should be dumped at least 100 yards from the greenhouse.

Condensation on the underside of the greenhouse top and on leaf surfaces creates conditions that favor disease. This condensation often results from a difference in temperature between the inside and outside of the greenhouse, particularly at sunset. Ventilating the greenhouse near sunset with horizontal airflow fans will help reduce potential condensation. Minimize overhead watering and potential splashing of media from one tray cell to another. Correcting drainage problems in and around the greenhouse will also help avoid excess humidity.

Weekly application of 1/2 lb of Dithane DF per 100 gal of water (1 level tsp/gal) should start approximately 1 week after seedlings are big enough to cover the tray cells. Spray volume should increase from 3 to 6 gal/1,000 sq. ft. as plants grow. Fungicide application should continue until seedlings are transplanted.

Not seeding tobacco greenhouses and float beds until March, and eliminating any volunteer tobacco plants within these structures, should be an essential component of each growers' disease control plan. As a general rule, plants closely related to tobacco (tomatoes, peppers, etc) should not be grown in greenhouses used for transplant production.

SPECIFIC DISEASES IMPORTANT IN VIRGINIA

Black Root Rot:
Roots of infected plants are usually black in color and decayed, causing plants to grow poorly early in the growing season. Plants may appear to recover as the season progresses and temperatures increase. Black root rot may be controlled by keeping soil pH between 5 and 6, planting a resistant variety, avoiding early planting into cold soils (65°F), promoting good soil drainage, and using a 3-year rotation with small grains or corn. Red clover, soybeans, or other legumes should not be planted in black root rot infested fields.

Black Shank:
Any activity that moves soil from one place to another can spread this disease. Control practices should vary according to the number of plants expected to die from the disease. The following table presents generally appropriate practices to control different levels of black shank:

Severity Level	Control Option
Low (Less than 60 plants/acre)	Use a 2-3 year rotation and a moderately resistant variety (4-6 on the KY/TN scale).
Moderate (60 to 300 plants/acre)	Use a 3-4 year rotation with a moderately resistant variety. One to two applications of a recommended soil pesticide may be necessary if rotation length can't be increased.
High (more than 300 plants/acre)	Use a 4-5 year rotation with a resistant variety. Several applications of a recommended soil pesticide should also be made.

Black shank control with Ridomil Gold or Ultra Flourish improves when part of the fungicide is applied before transplanting, part at the first cultivation, and the rest is applied at layby.

Root-Knot and Lesion Nematodes are microscopic worms that live in the soil and feed on tobacco roots. Significant nematode problems are usually found in fields continuously planted with tobacco. Selection of rotation crops is very important. Legumes such as red clover, vetch, and soybeans are as susceptible to root-knot and lesion nematodes as tobacco. NC 2, NC 3, NC 4, and NC 5 are resistant to common root-knot nematodes.

Blue Mold:
Obtaining transplants locally will reduce the chances of introducing blue mold from tobacco production areas outside Virginia. Application of blue mold fungicides should begin as soon as disease has been predicted for your area by the Blue Mold Forecast System and local Extension advisories. Dithane and Acrobat must be applied using high pressure (~ 100 psi) and large amounts of water per acre. Diaphragm or piston pumps may be required to maintain adequate spray pressure. The following table illustrates the spray volumes required.

Crop Stage	Gallons of Spray Mixture/Acre
	Air blast Sprayer	Hydraulic Sprayer
Before layby	10	20
Near layby	20	40
Waist-high plants	30	60
Chest-high plants	40	80
Near topping	50	100

Hollow cone (D3-23 or D3-25, for example) or disk-core (TX10 or TX 12) type nozzles should be used to ensure thorough coverage of all leaves.

Air blast sprayers can be used for small plantings. Fungicides should be mixed at twice the normal concentration when an air blast sprayer is used. However, spray volumes should be cut in half when using an air blast sprayer.

Complete coverage is not required when Actigard is used for blue mold control. However, tobacco plants need 4-5 days after application of Actigard before they are fully protected from disease. Initial use of Actigard should occur within 3 days of any previous fungicide application. If this is not possible, tankmixing the first Actigard spray with a fungicide will also help protect your crop while the plants are developing "systemic acquired resistance" to blue mold. Burley tobacco is sensitive to Actigard. Growers should follow the Actigard label very closely to minimize potential yellowing or stunting of the crop.

Regardless of the spray method used, applications of Dithane or Acrobat must be repeated weekly until blue mold is no longer a threat. However, Dithane and Acrobat may not be applied to burley tobacco within 30 days of harvest. The preharvest interval for Actigard is 21 days. Products such as bleach and household cleaners may appear to control the disease at first, but have actually made blue mold problems worse in University tests.

Brown spot, Frogeye, Target Leaf Spot, and Ragged Leaf Spot:
Soil compaction, improper pH, nematodes, root diseases, and poor sucker control are often associated with epidemics of these diseases. Excessive fertilization should also be avoided. Cultural practices such as crop rotation and early destruction of tobacco debris reduce overwintering populations of the fungi that cause leaf diseases. Wider plant spacings can also help reduce leaf disease problems. No fungicides are available for control of these diseases. Losses from tobacco leaf diseases are most often minimized by harvesting quickly once the disease has been recognized as a problem.

Tobacco Mosaic Virus cannot be eliminated without crop rotation and early root destruction or use of mosaic-resistant varieties. Most burley varieties are resistant to tobacco mosaic virus. Use of manufactured tobacco products in the plant bed, greenhouse, and field should also be strongly discouraged. Washing hands with a 1% solution detergent about every half hour while handling transplants can also help reduce the spread of mosaic. If old boxes must be used, they can be decontaminated by scrubbing with a 1% detergent solution. Plants showing symptoms of mosaic before the first cultivation should be removed to prevent spread of the disease.

APPLICATION METHODS

The performance and safety of a chemical depends on proper application methods. Improper use of agricultural chemicals can reduce yields as severely as any pest and will not provide satisfactory disease control. Proper pesticide use depends upon correct diagnosis of the problem, a clear understanding of the label for each chemical being applied, adequate calibration of application equipment, and strict adherence to label directions and all federal, state and local pesticide laws and regulations.

Preplant Incorporated (PPI) - Refer to section under weed control.

Foliar Spray - Plant Bed applications should begin when plants are about the size of a dime. Applications should be repeated if sprays are washed off by rain or irrigation. Greenhouse applications should start when plants are large enough to cover the cell surface in which they reside. Field applications should be made when disease is predicted or threatens and repeated at 7-day intervals. Applications should also be repeated after rain. A disc-core (D3-45, etc.) or hollow-cone (TX-12) type nozzle should be used to apply foliar sprays to burley tobacco. Foliar fungicides should be applied at 100 psi in 20 to 100 gallons of water per acre. Both the tops and bottoms of leaves need to be covered. As the plants increase in size, the amount of water per acre should also be increased in order to get adequate coverage. The use of drop nozzles for field sprays will also help increase coverage.

Fumigation: - F-Row - Inject fumigant 6 to 8 inches deep with one chisel-type applicator in the center of the row. Soil should be sealed in the same operation by bedding the fumigated row area with enough soil to bring the soil surface 14 to 16 inches above the point of injection. F-Broadcast - Space chisels 8 inches apart and inject fumigant 10 to 12 inches below the soil surface. Soil should be sealed immediately with a roller, drag, or similar piece of equipment.

Precautionary and Restriction Statements - Take labels seriously. Read and follow all directions, cautions, precautions, restrictions, and special precautions on each product label. This publication must not be used as the only source of precautionary and restriction statements.

DISEASE RESISTANCE LEVELS OF SELECTED BURLEY VARIETIES¹

	Black Shank
	Rating for Race 0		Rating for Race 1
Variety	Verbal	KY/TN2	Verbal	KY/TN2	Black Root Rot	Fusarium Wilt	Tobacco Mosaic Virus	Wildfire	Brown Spot	Blue Mold	Aphid Transmitted Viruses
KT 200	M	6	M	6	H	S	H	H	--	S	M
HB 04P	S	0	S	0	H	--	H	H	--	S	S
KY 8959	S	1	S	1	H	S	S	H	--	S	M
KY 907	L	2	L	2	H	M	H	H	--	S	M
KY 910	H	10	M	4	H	L	H	H	--	S	S
VA 509	M	5	M	5	L	L	S	H	VS	S	S
HY 502	M	4	M	4	H	L	S	H	--	S	S
Clay's 403	S	0	S	0	M	M	H	H	--	S	S
Coop 313	S	1	S	1	MH	--	H	H	--	S	S
PF 561	M	5	M	5	H	L	H	H	--	S	S
B 21xKY 10	S	0	S	0	L	L	H	H	S	S	T
KY 14xL8	H	10	S	0	M	M	H	H	T	S	S
R-6304	M	4	M	4	M	L	H	H	--	S	M
R-711	S	0	S	0	M	L	H	H	--	S	S
R-7124	S	0	S	0	H	S	H	H	--	S	S
TN 86	M	4	M	4	H	S	S	H	--	S	M
TN 90	M	4	M	4	H	S	H	H	--	S	M
TN 97	M	5	M	5	H	S	H	--	--	S	M
NC 3 3	L	2	L	2	H	S	H	H	--	VS	L
NC 4 3	L	2	L	2	H	M	H	H	--	S	M
NC 5 3	H	10	M	4	H	S	H	H	--	S	M
NC 20004	S	0	S	0	S	--	H	H	--	M	S
NC BH-129	S	1	S	1	H	S	H	H	--	S	S
1 VS=very susceptible; S=susceptible; L=low resistance; M=moderate resistance; H=high resistance; T=tolerant. 2Rating on a 0-10 scale where 10=most resistant; Developed by the University of Kentucky-University of Tennessee Tobacco Task Force. 3Resistant to races 1 and 3 of the common root-knot nematode (Meloidogyne incognita). 4Tentative ratings base upon the limited information, ratings may change in the future.

PLANT BED FUMIGANTS

Disease	Chemical	Product	Rate/100 sq yds	Remarks
Nematodes and diseases	methyl bromide (98%) + chloropicrin (2%)	Brom-0-Gas (cans) Terr-0-Gas 98 (cylinders)	9.0-18.0 lb	Fall fumigation is preferred. Prepare seedbed as you would for seeding. You must use an airtight cover. Treat at soil temperature above 55oF. Expose soil to chemical for at least 24 hours and then aerate 24 to 48 hours before seeding. The hot-gas method will permit shorter exposure time. METHYL BROMIDE IS EXTREMELY POISONOUS. Use higher rates for disease and nematode infestations. Read precautionary statements.
	methyl bromide (69%) methyl bromide (66%) + chloropicrin (33%)	MBC Terr-0-Gas 67 Tri-Con 67/33	7.7-11.0 lb 13.5 lb 9.3 lb	Aerate for 2 weeks before seeding.
Nematodes, insects, weeds, damping-off, black shank	metham (32%) (SMDC) metham (42%) (SMDC)	Vapam Metam CLR Sectagon 42	1.5 gal 1.1 gal 1.25 gal	Fall fumigation is preferred. Prepare seedbed as you would for seeding. Apply to freshly prepared moist soil when temperature is above 55o F. Tarp Method: Inject chemical to a depth of 5 inches or spray or drench in 40.0 gal of water per 100 sq yds. Apply uniformly over the entire area. Cover area immediately with plastic no less than 1 day, but no more than 2 days. After removing plastic, cultivate soil lightly and wait 21 days prior to planting in treated area. Read precautionary statements.

FOLIAR DISEASES OF TOBACCO SEEDLINGS

Disease	Chemical and Formulations Active Ingredient	Rate	Remarks
Tobacco Mosaic Virus (TMV)	Milk (whole or skim) Milk (dry skim)	5 gal/100 sq yd of bed 5 lb in 5 gals water /100 sq yd	Spray plants in plant bed from 1 to 24 hours before pulling. Should be combined with washing hands with phosphate detergent.
	Phosphate detergent	1/2 cup /gal of water	Wash hands every 15 minutes during transplanting operations.
Anthracnose (Colletotrichum gloeosporoides) Blue Mold (Peronospora tabacina) Target Spot (Thanatephorus cucumeris)	Dithane DF 0.5 lb/100 gal (1 level tsp/gal)	Foliar Spray	Apply as a fine spray to the point of run-off to ensure thorough coverage. Begin applications before disease has been observed, but not before seedlings are the size of a dime. Use 3 gal of spray mixture /1000 sq. ft. (or 100 sq. yd.) when plants are about the size of a dime. Use 6-12 gal /1000 sq. ft. (or 100 sq. yd.) when the canopy has closed and plants are close to ready for transplanting. Repeat applications on a 7 day interval to protect new growth.
Angular Leaf Spot or Wildfire (Pseudomonas)	Agrimycin 17, Agri-strep, etc. 100-200 ppm (2-4 tsp/3gal)	Foliar Spray	For blue mold suppression in plant beds (only).
Pythium Root Rot (Pythium spp.)	Terramaster 35WP	2 oz/100 gal of float bed water	Can be used before or after symptoms appear, but no earlier than 2 weeks after seeding. If symptoms reappear, a second application can be made no later than 8 weeks after seeding. MUST BE EVENLY DISTRIBUTED; when mixing, first form dilute slurry, then distribute slurry evenly and thoroughly in float bed water.

FIELD DISEASES OF TOBACCO

Root and Stem Diseases

			Disease2
Product	Rate/A	Application Method1	Black Shank	Black Root Rot	Granville Wilt
Ridomil Gold EC	2 pt	Preplant	F	---	---
Ultra Flourish	2 qt	Preplant	F	---	---
Ridomil Gold EC	1.0 pt + 1.0 pt	Preplant + layby	G	---	---
Ultra Flourish	2 qt + 2 qt	Preplant + layby	G	---	---
Ridomil Gold EC	1 pt + 0.5 - 1.0 pt + 0.5 - 1.0 pt	Preplant + 1st cultivation + layby	VG	---	---
Ultra Flourish	1 qt + 1-2 qt + 1-2 qt	Preplant + 1st cultivation + layby	VG	---	---
Telone C 17	10.5 gal	F-Row	F	F	G
Chlor-O-Pic	3 gal	F-Row	F	F	G
Chloropicrin 100	3 gal	F-Row	F	F	G
Tri-Con 67/33	6 gal	F-Row	F	F	G
Terr-O-Gas 67	6 gal	F-Row	F	F	G
1 F-Row ‚ inject 8 inches deep in row with single shank in center of row. Do not use more than a total of 3 qt of Ultra Flourish, or 3 pt of Ridomil Gold EC per acre. Drop nozzles should be used to apply these fungicides at layby. 2Control rating - F=fair; G=good; VG=very good. (X) - Will reduce disease losses but no current information on disease control performance. (-) - No disease control or not labeled for this disease.

FIELD DISEASES OF TOBACCO

Foliar Diseases - Blue Mold

Chemical	Material	Rate1	Application Method2	Comments
Systemic Fungicide Acibenzolar-S-methyl	Actigard 50WP	0.5 oz/20 gal/A	Foliar	Do not apply to seedlings. Treated plants require 4-5 days to fully respond to each application. Only 2 sprays are allowed; the first when plants are 18 inches tall, and the second 7-10 days later.
Mefenoxam	Ridomil Gold EC Ultra Flourish	0.5-1 pt + 0.5 pt/A 1-2 pt + 1 pt/A	Preplant + Layby Preplant + Layby	Most strains of the blue mold pathogen in 1995-2001 were insensitive to mefenoxam. However, mefenoxam will control sensitive strains early in the season, as well as Pythium damping-off. Read precautionary and rotation crop restrictions.
Protectant Fungicide Dimethomorph and Mancozeb Mancozeb	Acrobat MZ Dithane DF	2.5 lbs per 100 gal of water 1.5 - 2.0 lbs per 100 gal of water	Foliar Spray Foliar Spray	Begin sprays when the Blue Mold Advisory predicts disease and continue on a 5-7 day interval until the threat of disease subsides. Apply 20 to 30 gal/A of spray solution during the first month after transplanting. Gradually increase spray volume as the crop grows. Spray volumes should range between 80 and 100 gal/A on tobacco ready to be topped. Do not exceed 2.5 lb/A of Acrobat per application or 10 lb/A per season. Do not apply after the early button stage or within 21 days of the first harvest.
1Use higher rates of protectant fungicides for mature plants. 2Foliar spray - apply at 40-100 psi in 20 to 100 gal of water. The amount of water depends on size of plant. Use hollow-cone nozzles (TX12, etc.) Use drop nozzles to apply fungicide to both the top and bottom leaves. Preplant + layby - first application preplant followed by a second spray just before last cultivation.

FIELD DISEASES OF TOBACCO There Are No Chemical Controls For the Following Diseases:

Disease	Comments
Botrytis Blight (Botrytis cinerea)	This disease is restricted to tobacco greenhouses. A wet rot is often first observed on stems or leaves. A gray, downy material may be present on the surface of diseased areas. The only control methods available involve reducing surface moisture on leaves and stems (by correct watering and improving ventilation) and by collection and removal of loose leaf material resulting from transplant clipping operations.
Brown Spot (Alternaria alternata)	Can be severe on mature tobacco, especially during periods of high humidity. Avoid practices that would leave mature leaves in the field or delay the maturity of the tobacco. Harvest early when lesions appear on dry leaves.
Collar Rot (Sclerotinia sclerotiorum)	Symptoms of this disease (occurring only in greenhouse and float bed systems) resemble damping-off. Small groups of plants have brown, wet lesions near the base of stems. Leaf rot may be seen that appears to progress from leaf margins or tips toward the stem. White, cottony, mold may be visible. Irregularly shaped, white to black objects (sclerotia) may also be found attached to severely infected plant parts. Sclerotia may be carried to the field by infected plants. Infected plants, as well as plants immediately adjacent to diseased areas, should be discarded as soon as possible. Improving ventilation and reducing excess moisture will help reduce spread of the causal organism. Proper clipping procedures may also help.
Frenching (nonpathogenic causal agent)	This disorder has been associated with toxins produced by a nonpathogenic bacterium, Bacillus cereus, and other nonpathogenic microorganisms. Frenching is more prevalent on wet, poorly-aerated soils. This problem can be more severe on neutral or alkaline soils and is sometimes associated with lack of available nitrogen or other minerals. Proper drainage and fertilization can be beneficial. Do not plant in alkaline soils and avoid heavy applications of lime.
Frog Eye (Cercospora nicotianae)	Avoid overfertilization with nitrogen. Use a 2-year rotation and be sure to plow refuse under early.
Ragged leaf spot (Ascochyta nicotianae)	Can be severe on green as well as mature tobacco. This disease may appear anytime during the mid- to latter part of the growing season. Severe epidemics will only occur when fields, and especially the leaves, remain wet for prolonged periods of time. No fungicides or resistant varieties are available. Harvesting mature tobacco promptly and minimizing crop stress are the best controls known at this time.
Southern Stem and Root Rot (Sclerotium rolfsii)	This disease often occurs first in the plant bed, so disinfecting the bed is important. Choose disease-free transplants. There is no field control. Resistant varieties are not available.
Target Leaf Spot (Thanatephorus cucumeris)	Can occur in greenhouses, plant beds, and in the field. Can be severe on green, as well as mature tobacco. Severe epidemics only occur when leaves remain wet for prolonged periods of time. No resistant cultivars are available. Improving watering and ventilation of transplants, harvesting mature tobacco promptly, and minimizing crop stress are the best controls known at this time.
Viruses (mosaic, vein-banding, tomato spotted wilt, etc.)	Once a plant is infected, it remains infected for life. See special note on viruses.
Weather Fleck (ozone)	This disorder appears as small brown to tan leaf spots in the plant bed and field. The major cause of this problem is ozone from car, industrial, and natural sources. Hot humid days followed by heavy rains increase severity of problem.
Wildfire, Angular Leaf Spot (Pseudomonas tabaci and P. angulata, respectively)	Rotation is recommended. Streptomycin sulfate is used in the plant bed to obtain bacterial-free transplants. In addition, streptomycin sulfate can be used in the field.

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Weed Control in Burley Tobacco

Good weed control uses crop rotation, early root destruction, cultivation, and appropriate use of herbicides. Most weeds found in tobacco fields can be controlled by several cultivations. However, poor weed control may result when rain prevents cultivation 1 to 3 weeks after transplanting. Use of a herbicide will reduce dependence on the first cultivation for early season weed control. The number of cultivations can often be reduced when a herbicide has been applied. Some herbicides may also be applied to the row middle after the last cultivation to obtain full season weed control. Herbicide use should be based upon the specific weeds present in each field, the weed control program that integrates best with overall farm management practices, and herbicide cost in relation to performance, crop safety, and anticipated rotational crops. Herbicide performance and safety are dependent upon the use of correct application methods. Special effort should be made to apply all herbicides exactly as stated on the product label.

IMPORTANT CONSIDERATIONS IN HERBICIDE USE

Selecting the Proper Herbicide
Weed Identification - Identifying the problem weeds in each field should be the first step in any weed control program. The majority of herbicides used in tobacco will control grasses and a limited number of broadleaf weeds. Check herbicide labels to ensure that the products are active against the desired weeds.

Use of herbicides with rotation crops may reduce populations of hard-to-control weeds in tobacco fields and avoid some of the problems associated with use of tobacco herbicides. The table on page 48 is a summary of herbicide performance for weeds found in burley tobacco fields in Virginia.

Soil Texture and Organic Matter Content - Herbicide rates should increase as percent organic matter increases and as soil texture changes from coarse to fine. However, the lowest recommended rate should always be used when percent organic matter is less than 1%, regardless of soil texture. The soil textures listed in herbicide labels and recommendations are as follows: Coarse Soils - sands, loamy sands, and sandy loams; Medium Soils - sandy clay loams, loams, silt loams, and silts; Fine Soils - clay loams, silty clay loams, and clays. The percent organic matter of your soils can be determined by taking a soil sample and submitting it to a soils laboratory for analysis.

Proper Herbicide Application
Soil Preparation - Most herbicides used in tobacco fields control weeds by preventing seed germination. Already established weeds are not significantly affected. All weed growth and crop stubble should be thoroughly worked into the soil prior to application of a tobacco herbicide. Soil should be moist and loose, with all clods broken up, before a herbicide is applied.

Spray Equipment - A standard low-pressure (25 to 50 psi) boom sprayer should be used to apply herbicides in 20 to 40 gallons of water per acre. Check for clogged nozzles and screens frequently while spraying. Use 50-mesh screens in strainers, nozzles, and suction units. Clean or replace dirty or worn out sprayer, boom, and nozzle parts to ensure uniform application. Be sure to calibrate the sprayer before use to avoid crop injury and/or poor herbicide performance. Ensure that the spray solution is continuously agitated. Do not apply a herbicide in strong wind, since wind can cause uneven coverage. Never leave a spray mixture in a sprayer overnight!

Herbicide Incorporation - All herbicides should be incorporated as soon after application as possible. Avoid using a large field disc to incorporate PPI herbicides. Use a combination, tandem, double disc, or disc harrow set to cut 4 to 6 inches deep. A disc set to cut 4 to 6 inches will incorporate a herbicide in the top 1 to 2 inches of soil. Shallow incorporation with implements set to cut less than 2 inches deep can result in erratic weed control. A disc operated only one time does not incorporate a herbicide adequately. Incorporating equipment should be operated in two different directions, at right angles to each other, at 4 to 6 mph. Discs should be no more than 24 inches in diameter and 8 inches apart. P.T.O.-driven equipment (tillers, cultivators, hoes) perform best on coarse soil types. P.T.O.-driven equipment should be set to cut 3 to 4 inches deep and should not be operated at a speed greater than 4 mph. Tillage or irrigation is often required to incorporate tobacco herbicides applied after transplanting. Using incorporation equipment and/or tractor speeds not listed on the product label may result in poor or erratic weed control and/or crop injury.

Undesired Effects of Herbicide Use
Effect of PPI Applications on Early Season Tobacco Growth - PPI herbicides can sometimes inhibit root development of transplants, delaying plant growth during the first month after transplanting. However, diseases, insects, unfavorable growing conditions, poor transplants, fertilizer and/or fumigant injury can also delay early season growth and development of tobacco. Possible early season growth reductions by herbicides can be avoided by surface application at transplanting or layby.

Effects of Herbicides on Rotation Crops - Residues from some tobacco herbicides may reduce growth of crops following tobacco. These effects are discussed in the labels for the particular herbicides involved. Potential carry-over can be reduced by: 1) using the minimum labeled rates for the chemical, for your weed problems, on your soils; 2) applying herbicides at transplanting and/or layby rather than PPI; and 3) deep plowing before seeding the fall crop.

Plant Bed Herbicides
Adequate weed control in burley tobacco plant beds can usually be obtained by fumigation. Poast herbicide may be applied to control emerged grasses. Special care is needed when mixing Poast. First fill the sprayer with 1/2 to 2/3 of the water needed to make the application. Add the oil concentrate first, then Poast, and then the remaining volume of water. Agitation must be maintained continnously while mixing and applying Poast. Don't apply Poast: (1) at rates above 2 tsp (0.33 oz.)/100 sq. yd. of plant bed; (2) more than once per season; (3) to grasses under stress; (4) if rainfall is expected within 1 hour; (5) with any other pesticide, additive, or fertilizer except as specified on the Poast label; or (6) through any type of irrigation system.

Preplant Incorporated Herbicides (PPI)
Apply the herbicide in an even broadcast application. Avoid spray overlap! Use fan-type (8004, etc.) or flood-jet (TK2, TK4, etc.) nozzles. Incorporate the herbicide immediately after application using recommended equipment.

Over-the-Top After Transplanting (OT) & Layby Herbicides
An OT application can be made as either a band or broadcast application within 7 days of transplanting. Tillage is required immediately before or at the time of an OT application if the application is made more than 2 days after transplanting or if rain has fallen or irrigation was applied since the crop was transplanted.

1. Band Application - Apply the herbicide in a 14 to 24 inch band over the top of transplants during transplanting. Use fan-type, even-spray nozzles (8004E, etc.). The amount of herbicide required per acre of crop is reduced with band application and can be determined by the following formula:
   Lbs of Band Width (inches) Broadcast Rate
   Product/Acre = Row Spacing (inches) x in Lbs/A

2. Broadcast Application - Apply the herbicide in an even broadcast application using a sprayer equipped with fan-type nozzles (8004, etc.). Be sure to use the recommended amount of product per acre.

PRECAUTIONARY AND RESTRICTION STATEMENTS