Raising Tobacco Plants from Seed

New Zealand Journal of Agriculture, Volume 89, Issue 5, 15 November 1954, Page 489

Raising Tobacco Plants from Seed

TWO methods of raising tobacco plants are practised in the Nelson district. Boxes of • plants may be bought from a nurseryman and pricked out into beds, or the seed may be sown directly into seedling beds and the plants raised there without any further handling. The latter method is gaining favour and has the advantage of greatly reducing mosaic through less handling of seedling plants. The following article by R. Thomson, Tobacco Research Station, Department of Scientific and Industrial Research, Umukuri, describes methods developed by the Research Station and put,into practice successfully by many growers.

THE foundation of a good tobacco crop is a plentiful supply of sturdy disease-free plants, ready at the correct time for setting out in the field. Many diseases and insect pests have their origin in the seedling beds, from where they are carried to the field and disseminated. Uniformity is an important factor and this can best be achieved by providing ample bed area so that there are plenty of plants to pull from. Plants of mixed sizes or varying vigour cause trouble from start to finish. They are unsuitable for use with a planter; and because many weak or diseased seedlings will die, considerable replanting will be necessary, resulting in an uneven crop, ,with consequent difficulties in harvesting and curing, to say . nothing of loss in yield. Location The site for the seedling beds should be chosen carefully. It should be close enough to the house or farm buildings to be under constant supervision. A more remote location may have other desirable features, but the site selected should be one that can readily receive attention at any hour of the day, particularly in adverse weather. On. the other hand it should not be so close to the bulking and grading sheds that it is likely to become contaminated by tobacco refuse. The proximity of stock, dogs, and fowls must also be considered, and it may be necessary to fence off a desirable location to exclude these. An adequate water supply is another essential. During growth

tobacco seedlings are likely to require frequent watering and if a plentiful and easily applied supply is not available, this important job is likely to be neglected, with disastrous results to the plants. Most water in the Nelson district is from underground sources, and is free from contamination. However, should water from a pond or stream be used, it is essential to make sure that it is not fed by run-off from tobacco fields. The spores of diseases like verticillium wilt and Phytophthora canker can be carried by surface run-off, and contaminated water could spread disease to otherwise healthy beds. The bed site should be well drained, provision being made to get rid of surplus rainfall rapidly. Tobacco plants will not stand wet feet, and a low area or a tight, puggy soil should be avoided. Waterlogging excludes the air from the soil, causing decay of the roots, and the plants soon become yellow and stunted from starvation. Excess moisture is also favourable to the growth of fungi such as those causing collar rot and damping off. When choosing a site it is better to err on the dry side and to have to water frequently than to utilise a poorly drained location. Shade on the beds at any time of the day should be avoided. The aim is to keep the plants growing rapidly and vigorously, and any shading, with a consequent lowering of temperature and light intensity, will result in soft, weak growth. The location of the beds should be reasonably level, any slope being toward the north so that the

beds will receive a maximum of sunlight. Excessive slope will tend to allow water to run on the beds and cause surface washing. A windbreak to the south will keep cold wind off the beds and protect the covers from damage. Windbreaks on any other side are beneficial, but should be sufficiently far away not to cause any shading. Construction Beds should run north and south so that both sides receive equal sunshine. Beds lying east and west usually have strong plants along the north side, but plants on the south side become progressively weaker because they are increasingly shaded. Seed-beds can be any length to suit the location. The usual width is 4ft., but a few inches less may be an advantage, as this allows a greater pitch on the covers, which are all a standard width of 54in. This extra pitch allows a better run-off of surplus rain, which is inclined to collect and drip through flat covers. The sides can be made of Bin. x tin. timber let 2in. into the ground. They can be stayed by pegs driven in at intervals of about 6ft. It is preferable to use flat pegs, as these cause less wear and tear on the covers and are more easy to cope with should it be necessary to cover the beds for chemical sterilising (see section on sterilising on page 491). Ends should be gable shaped, with the peaks Bin. to 12in. higher than the sides, and a wire should be stretched from end to end .to support the calico covers. Tension on these wires is usually adjusted by fastening the wire to a peg outside the end of the bed and driving the peg into the ground to

take up the slack. On long beds the small ratchet type of wire strainer has proved very useful for keeping wire tight. Where old bed timber is used it should be thoroughly cleaned down between seasons and preferably sprayed with a 2 per cent, solution of formalin. Old covers should be boiled for 20 minutes as a precaution against carrying over disease from season to season.

The beds should be filled with soil to about half the depth of the boards. The level of the soil inside the beds should always be above that of the surrounding paths so that drainage will be from the beds outward and never the reverse. Soil for the beds should be a free-working sandy loam well supplied with organic matter. Lighter soils will serve, but they dry out more readily and require more attention and more frequent. watering. Heavy soils are unsatisfactory. At this stage the beds should be dug or forked over deeply, all lumps broken down, and the surface raked reasonably level.

Sterilisation

When tobacco plants are being raised directly from seed some form of soil sterilisation to kill weeds is almost essential. Depending on the facilities available, one of three methods steaming, burning,' or chemical sterilising—may be used.

Steam Sterilisation

Steam sterilisation is the most effective for the control of both weeds and soil-borne diseases, but it can be carried out only where a steam boiler and equipment are available. For steaming to be done satisfactorily the soil should have about the same moisture content as would be considered suitable for ordinary cultivation. If it is drier, the steam will escape without doing its work, and if it is too moist, the soil will be turned to mud and the structure ruined. Either the grid method or the inverted-pan method may be used. For steaming a great depth of soil, usually under cover in a shed or lean-to, the grid method is probably the better, but for steaming beds in position the shallow pan is to be preferred. Whichever method is used, the main thing is to raise the temperature of the soil to 200 degrees F. or more and maintain it at that for some time.

The length of time required to do the job will depend on the size of the boiler and the pressure of steam; the governing feature is that the soil temperature must be raised to 200 degrees F. As steaming builds up the ammonia in the soil, with a risk of injury to the young seedlings, it is advisable to allow 10 days between steaming and sowing. Tobacco appears to be less sensitive in this respect than other plants, however, and if this delay is likely to make seeding unduly late, a thorough aeration of the soil by forking over should minimise the risk. The minimum of sterilised soil should be 3in., but more is preferable.

Burning

Piling scrub and brushwood on the beds and burning it will kill weed seeds in the top inch of soil. A more effective method, however, is to dig a pit and fill it with firewood. Sheets of iron are then laid over this and the

soil heaped on to them, a wall of sods round the edge generally being used to contain the soil, which is then covered with more iron. The wood is set alight, and by control of ventilation a slow fire is obtained which will last for several days, effectively sterilising the soil. Chemical Sterilisation Methyl bromide: Excellent results have been obtained by this method. The beds are laid down in the usual manner and prepared as for sowing by deep digging over, breaking down of lumps, and raking level. They are Plastic el sheet ed Sff Seal but laminated o building naner wfil do b The Tovers are stretched into nlace over the beds with a wire O? boards running beets, with to wire a boards running lengthwise to form a ridge. The edges of the covers are sealed all round by soil shovelled on to them Before the beds are finally sealed it is necessary to provide tubes for introducing the methyl bromide. Two-hundred square feet of bed can be treated at one “shot”, and therefore in the ordinary -wide bed it i? lecessarv to have delivery tubes for every 50ft. of length wKen the methyl bromide is in small containers it is liberated in liquid form. In this case the inner end of the delivery tube should rest in a shallow tray or pan to allow the liquid to collect and evaporate. ' Large cylinders have both

gas . and liquid outlets. When gas is used the tray is not necessary. The rate of application is lib. per 100 sq. ft. of bed. The covers should be left in place for from 48 to 72 hours, the shorter period being sufficient during warmer weather. There are no toxic after-effects and seed may . be sown as soon as the covers are removed. Methyl bromide is highly poisonus and is colourless and odour- ? ess - It can be obtained con tain- } n £ 2 per cent, chloropicrin as a lachrymator indicator and this mixture should always be used. If is handled entirely in the open with the operator standing on the windward side of the apparatus and remaining upright all the time (the g as J* up*™™, r S n alr) - there should air} ’ tfteie snou be no undue risK. Calcium cyanamide is a fertiliser containing 20 per cent, of nitrogen, but jt also has given good results in controlling weeds. plied to the sol. in large quantities it is toxic to plant a *in therefore must be applied well in advance of the time the seed is sown, For a number of years it was unobtainable locally,. but is now back on tne niarxei. The beds are put down and prepared in the usual way. The calcium cyanamide is applied at the rate of lib. per square yard of bed. Threequarters of this amount should be

distributed over the surface of the bed and forked in; the remaining quarter is then spread over the surface and lightly raked in. This should be done 90 days before the seed is sown.

Moisture is required for the chemical action of the calcium cyanamide and also for the subsequent leaching from the soil, so it is essential to water the beds freely after the application and during the intervening period before seed sowing if rain does not fall. This is most important if toxic after-effects are to be avoided. Most failures can be attributed directly to dry conditions. Because of the high nitrogen content of calcium cyanamide it is advisable to use only superphosphate and potash as fertiliser subsequently.

Where no facilities are available for sterilising it is a good plan to prepare the beds several weeks before they are required, water them thoroughly, and put the covers in place. This .method will germinate a lot of weed seeds, which can be killed by frequent hoeings before the beds are seeded. Whatever method is used the land should not be stirred deeply before sowing, as this will only bring up seeds from below and defeat the object of sterilising.

Fertiliser

An adequate supply of fertiliser is essential for the production of vigorous plants, but excess should be avoided or the plants will be soft and sappy. Most of the standard tobacco fertilisers are suitable, but mixtures low in nitrogen should be avoided. The rate of application should be fib. per square yard on steam-sterilised soil and lib. per square yard for unsterilised and burnt soil.

Where calcium cyanamide has been used the nitrogen should be omitted from the fertiliser and only superphosphate and potash used. The fertiliser should be broadcast evenly over the surface of the bed and worked in with a rake about a week before seeding. Evenness of distribution is essential; any irregularities will be evident in the subsequent growth of the plants.

Sowing the Seed

Seed is usually sown from the third week in August until the middle of September. This will provide plants from early November. After the fertiliser has been applied the beds should be raked as level as possible and then firmed with a roller or a board. Depressions left in the surface at this stage will cause trouble at subsequent waterings, and a wellconsolidated bed is essential for a satisfactory stand. After it is firmed the bed should be watered thoroughly. It is easier to do this job before the seed is sown than to try to make up deficiencies by later watering.

Forty feet of bed should provide sufficient plants for each acre. Wellcleaned seed of high germination should be used. One-year-old seed will usually give a more uniform germination than new season’s seed. The usual rate of seeding is 1 level teaspoon to 200 sq. ft. of bed. Teaspoons vary in size, but a mediumsized spoon should be used and the seed struck off level. On no account should this rate of seeding be exceeded; it can be reduced with advantage.

The seed may be sown dry or in suspension in water through a watering can. For dry sowing the seed should be mixed with a quantity of clean dry sand; for each teaspoon of seed about i kerosene tin of sand should be used. The mixture should then be sprinkled thinly and evenly over the surface of the bed, the bed being gone over several times until all the sand and seed are used. For sowing with a watering can it is first necessary to pre-soak the seed, The seed should be measured out dry in units of quantity required for a bed length and these lots put to soak overnight m clean water. An ordinary 3-gallon can with a coarse rose will conveniently sow a 25ft. length of bed. The can should be filled with wa t? r i the measured quantity of soaked seed is then stirred in ana watered on to the bed, the can being moved ,all the time to keep the seed agitated. All the seed will go through with the water and a very even distribution can be secured. After being sown by either method the seed should be covered with a layer about jin. deep of clean fine sand and watered thoroughly. The sand protects the seed from drying out and also prevents its being moved by heavy watering. The sand used for sowing and covering should be sterilised by steaming or heating, as it is likely to contain weed seeds. Occasionally it may be desirable to sprout the seed before sowing it, particularly where sowing has been delayed or where the beds have not been sterilised. The sprouting will give the tobacco seedlings a chance before weeds come up. To sprout, the required. quantity of seed is first

sprinkled on to a piece of damp calico about 6in. square. This is made into a roll and moist flannel is wrapped round the calico and tied in place. The roll is then placed in a warm, not hot, position and kept moist; this may' be done by putting the roll in an ordinary preserving jar and screwing the lid on lightly. After 4 days the seed should be examined daily, and. when the majority of it is showing tiny white sprouts it may be sown in the usual way. Management of Beds The beds should be kept moist until the seedlings are up, and for this a daily inspection is necessary. Many failures are caused by beds being allowed to become too dry. Tobacco seed is very small and tender, and one dry day can seriously injure the germinating seed. This is the chief reason for thoroughly consolidating the ground before sowing; a loose surface dries out more readily than does a firm one. Once the plants are up the beds should be kept sufficiently moist, not unduly wet, to keep the seedlings growing rapidly. It is better to give a few thorough waterings than many light sprinklings. Watering should be done in the early afternoon so that the leaves are dry before evening. Excess moisture brings about conditions favourable to disease. Adequate ventilation is essential in raising sturdy plants and is the most practical means of keeping in check diseases like moulds and. damping off. Once the seedlings are up the ends of the covers should be opened ' up on fine, calm days to permit a current of air through the beds, As the . seedlings grow the beds can be opened

fully during the warm part of the day, though it may be necessary at times to protect them from the hottest rays of the sun. From then on the beds can be opened for a longer time each day, until eventually they are covered only at night or during rough weather. More harm will be done by keeping the beds too closed up than by opening them frequently. About a week before the seedlings are transplanted the covers should be left off night and day and watering reduced to harden off the plants for the field. Under some conditions the seedlings may be pale and slow in growth. This is more likely on open, sandy soil where the necessity of heavy watering tends to leach out the fertiliser. In such cases a supplementary dressing of nitrogenous fertiliser is required, and nitrate of soda, because of its quick action, is the most suitable. It should be dissolved in water and applied at the rate of loz. to the square yard. This should be followed by a watering with clean water to wash the nitrate off the leaves; otherwise burning may result. On account of the risk of burning with nitrate of soda some growers prefer to use dried blood. This should be applied at the rate of ljoz. per square yard and watered in. Diseases The seedling bed is often the source of infection for diseases in the field and therefore every effort should be made to keep the beds healthy. The following are the principal diseases likely to be encountered:—

Angular leaf spot is a bacterial disease which causes the familiar angular markings on leaves of plants in the seedling bed and later in the field, though the symptoms are not always typical and under varying weather conditions the type of spotting may vary. Angular leaf spot can be controlled in the beds by Bordeaux mixture. The mixture should be 3:4:50 (31b. of bluestone, 41b. of hydrated lime, and 50 gallons of water). The first application should be made when the plants are the size of a 3d. coin and should be put on with a watering can at 3 gallons per 100 sq. ft. of bed. It is as important to wet thoroughly the surface of the soil as it is to wet the leaves. This is the reason why the first application should be made so early and why a watering can is recommended in preference to a spray pump. A second application should be made 10 to 14 days after the first, and if stormy, rainy conditions prevail, a third may be desirable. Many growers do not wish to make up small lots of Bordeaux mixture, and these may use any certified Bordeaux substitute such as copper oxychloride or cuprous oxide wettable powders, made up at summer strength according to the manufacturers’ instructions. It is essential to weigh and measure the components of a Bordeaux mixture accurately and to keep the mixture well stirred or the foliage may be burnt.

Damping off, a common trouble of seedling beds, is caused by a fungus which spreads rapidly under humid conditions. Diseased seedlings shrivel up and collapse, and after lying on the soil for a day or two disappear. This disease generally affects patches of plants and spreads rapidly. The best method of preventing damping off is to seed thinly and allow plenty of ventilation. Watering should be done in the early afternoon so that the leaves can dry off before the cool of the evening. If the disease is present, the beds should be opened right up even if it means that they temporarily become dry. Patches of diseased plants should be removed with the surrounding plants and all affected soil. The area should then be treated with formalin solution (1 part of commercial formalin to 40 parts of water). Bordeaux mixture as applied for angular leaf spot is of some benefit in checking damping off.

Collar rot is another fungous disease. A black spot appears on the stem at ground level, and as the disease progresses the spot completely girdles the stem. Taking slightly infected plants to the field is frequently the cause of uneven stands and much replanting. If the disease is suspected in the beds, the plants should be looked over very carefully as they are pulled from the beds. Humid conditions in the beds favour the disease, and therefore light seeding and plenty of ventilation are precautionary measures. Sprays have not proved effective, but Bordeaux mixture has afforded slight protection.

Black root-rot is caused by a fungous disease which attacks the roots of the tobacco seedlings. Plants in the beds will generally appear stunted, yellow, and unthrifty. When they are pulled up the root system is seen to be poor with many of the roots showing blackening and rotting. Such infected plants should never be set out in the

field, as they may infect an otherwise healthy field. If black root-rot appears in the seedling beds, the beds should be moved to a new site the following year. Efficient sterilisation with steam or methyl bromide will control the disease. Mosaic: This virus disease is widely distributed and is well known to growers. There is no cure for it, but the raising of seedlings by direct sowing in the beds is the first step in its prevention. Mosaic is spread from plant. to plant by handling, and any plan which reduces handling is a practical step toward eliminating the disease. If mosaic is present in a seedling bed, the bed, or at least the affected portion of it, should be discarded, as the disease is certain to be more widespread than is apparent to the eye. Mosaic infection can be removed from the hands by washing with soap and running water. As a precaution it is recommended that when doing work such as weeding or pulling plants workers should wash their hands at regular intervals, particularly after an infected plant has been handled, and after smoking, as manufactured tobacco can carry the virus infection. ? Insect Pests Springtails are tiny black or brown insects about l/25in. long which jump vigorously like fleas when disturbed; they eat the leaves of the germinating seedlings and often do considerable damage, cleaning out large patches before being detected. They usually enter the beds from surrounding vegetation and weed growth. Spraying such growth with lime sulphur (1 part to 100 parts of water) will clean up this source of infestation. In the beds the insects can be controlled by dusting with derris dust at Joz. per square yard Or 2 per cent. D.D.T. dust at loz. to every 50 sq. ft. of bed. An effective control is to spray with nicotine sulphate at 1 fl. oz. to 4 gallons of water to which 2oz. of soft soap and 2oz. of wettable sulphur have been added.

Vegetable weevils are short, plump, pale-green grubs varying in size from a pinhead up to 3/16in. long. They are particularly destructive, as in addition to chewing the leaves they frequently attack the heart of the plant, eating out the growing point. From the seedling beds they can be transferred to the field, where they carry on their destructive work. They may be controlled by spraying with arsenate of lead (loz. of arsenate of lead powder and loz. of hydrated lime to 4 gallons of water) or by spraying or dusting with D.D.T. (Note: Wettable D.D.T. preparations vary in strength. The strength required is Jib. of actual D.D.T. to 100 gallons of water.)

Leaf miner: The seedling bed can be the centre of infection of this troublesome pest. The tiny caterpillars tunnel in between the upper and lower surfaces of the leaf, forming transparent patterns on the leaf, and eventually eat into the heart of the plant. As these insects feed beneath the surface, poisons like arsenate of lead are of no use. Contact poisons which will kill the tiny grub in the short interval between its hatching from the egg and burrowing into the leaf are the only effective means of control. Spraying with D.D.T. at gib. of actual D.D.T. to 100 gallons of water or dusting with 2 per

cent. D.D.T. dust are the recommended treatments. Cutworms are tiny pests which sometimes cause trouble in the seediin2 beds Thev are verv hard to detect; but if the plants are being eaten and no insects are apparent, cutworms should be suspected. They are best controlled by dusting over the bed with 2 per cent. D.D.T. dust at loz. to each 50 sq. ft. of bed. Slugs can cause extensive damage in seedling beds. Keeping the . site free from weeds and rubbish is the first f e p toward control. Metaldehyde fue tablets can be used as bait foi slugs . One tablet should be crushed U an( m d with a large cupful of bran. This should be sprinkled over the bed or placed in small heaps on the ground; it must be renewed after rain Or watering' b ' , Care o Beds between Seasons . „ . ~ „ , ~ , , As soon as a grower is satisfied that he as completed • his replanting his beds should be dismantled and the remaining plants destroyed. Taking HP . an stacking the boards prolongs their life and usefulness, and destroymg the plants prevents the carry over of disease and insect pests from season to season. Many abandoned beds are full of leaf miner and mosaic and are centres of infection for crops. o considerable should b kept clean cultivated Thi? will a a Rt Inis will „thZr nt pZts reseeding and slugs and buddin f O n the § site An Sterna U P ™ site. An alternas This iT auite a good cover Prided the Iro’p is turned unknot m'h'reak^'dnwn "wint r’Hvh n d 2omnoStion it fairlv slow ’ h Decomposition is fairly slow. AU photographs by W. C. Davies.

i 1 Book Review I g . nn tm u mii hi f

“Beef Production”: M. M. Cooper

THIS book is timely for both British and. New Zealand agriculture, since recent price reviews favour beef production in Britain. In general the beef industry of Britain, past, present, and future, is discussed adequately if somewhat controversially. After the customary introduction and history of the British breeds, breeding problems, growth and development of the animal, and fattening, found in numerous texts that attempt to write for the student, stockman, and agricultural economist simultaneously, are three chapters which deal with different types of beef enterprise. However, it is not until the final chapter that Professor Cooper, who has the reputation of complacency - breaking, outspoken criticism of the inadequacies of many British farming practices, summarises the problems and offers solutions. All interested in this subject should find the final chapter both thought provoking and stimulating. Thomas Nelson and Sons Ltd., London. 12s. 6d. —M. A. MacD.