The first recorded evidence of cotton in South Africa was in 1516, which was a wild species of cotton and is still found today. Cotton was first planted in the Western Cape in 1690 which was about 40 years after the arrival of Jan van Riebeeck. Much later in 1846, a man by the name of Dr Adams bought cotton seed in from America and started growing it in the Amanzimtoti area in Kwa-Zulu Natal.
|Commodity: a raw material or primary agricultural product that can be bought and sold.|
Two distinct types of cotton are grown commercially. The finest, strongest and longest lint is produced by the famous Sea Island type (Gossypium barbadense), grown in the West Indies and under irrigation in Egypt. The staple, the length of the lint or fibres, may be up to 50 mm long. The cotton grown in Southern Africa is the American Uplands type (Gossypium hirsutum), with a staple of 25 mm.
Cotton is an important commodity of the world trade. The main cotton producing countries are India, Egypt and the U.S.A. Although by world standards the amount of cotton produced in Central Africa is very small (1%), because of its high quality the local crop makes up a significant amount of cotton traded on the world market of about 25%.
Although the cotton plant is a perennial shrub and will produce a second crop if cut down and allowed to grow again a second year, it is grown as an annual, and all crop residues have by law to be destroyed each year to prevent any carry-over of pests and diseases.
The plant seeks moisture and has a very well developed deep root system with a tap root that can reach a depth of 2 metres within 2 months of germination. 40% of the active roots are in the top 300mm of soil and 65% in the top 600mm, however the plant can draw water from deep in the soil. Due to this deep rooting system, it is very susceptible to lack of air and to water logging and must be grown in deep well-drained soils.
2. DEVELOPMENT OF THE PLANT
Under normal conditions, the development of the plant follows this pattern:
Tabel 1: The Development of the Cotton Plant
|Planting to seedling emergence||7 – 10 days|
|Germination to 1st flower buds||6 weeks|
|First flower buds to first flowers||6 weeks|
|First flower buds to first flowers||8 ½ weeks|
|Fertile fruiting points are produced every||2 ½ days|
|Main flowering period is from||8 ½ to 16 weeks after planting|
The period from the first flower buds appearing to the ‘tailing off’ of flowering lasts about 10 weeks during which about 30 fruiting points will be produced on each plant. The order in which the fruiting points appear (and these produce the Cotton bolls), is shown in the diagramme below.
Figure 1: A growth line showing plant and flower development
Figure 2: Order in which fruiting heads are formed
Yields of cotton are always expressed as kg per hectare of seed cotton. This is the seed with the lint still attached. The expression ‘Ginning out Turn’ (G.O.T.) refers to the percentage of lint in the seed cotton. The G.O.T. should be about 33% or 1/3rd of lint.
Cotton is a sun loving plant and the higher the temperature the better the crop. The best growth is at temperatures over 26°C. Growth slows down when the temperature drops to 18°C and ceases below 12°C. Even night temperatures below 10 – 12°C will slow down growth and may stop the formation of lint. Temperature is related to altitude and cotton should not be grown at an altitude higher than 1 200 metres. There is no lower limit to the growing of cotton.
Any area which receives less than 600 mm of rain should not be considered for cotton growing without irrigation. Crops planted after the first planting rain usually require rain until the end of March for the top of the cotton plants to mature.
Cotton can be grown on a wide range of soils but for the best results at least 900 mm of well drained soil is required. The best cotton soils are the deep, red clay soils. But, provided the correct amounts of fertilizer are applied, the crop can be grown successfully on deep, sandy soils. Depth of soil and good drainage are the important factors, as cotton cannot survive waterlogged conditions. Cotton does not do well on acidic soils especially if the acidity is associated with aluminium therefore the pH of the soil should not be lower than 5.7.
Figure 3: A field of cotton growing well
The most important requirement for growing a successful crop is deep and thorough soil preparation, which is the foundation for high yields being laid when the soil is first turned. The soil should be ploughed at least to a depth of 250 mm and any plough pan below this depth should be removed by sub-soiling. All crop residues from the previous crop should be turned in and fully covered. The best time for ploughing is at the end of the rains and the ploughed land should be disced immediately. This helps to seal the soil surface, conserves the moisture in the soil and enables the ploughed-in crop residues to rot down during the dry season.
After the first rains or first irrigation the land should be further disced to produce a fine tilth and kill off germinating weeds. Cotton is a crop with a small seed and needs a fine tilth for even germination. It is slow growing in the early stages and cannot compete with weeds which shade out the crop and robs it of its nutrients and water. Soils with a tendency to ‘capping’ should be further cultivated to break up the ‘cap’ and allow rain to penetrate.
As it is so important to have a fine tilth for planting cotton, crop rotations must be considered. Maize does well after cotton taking advantage of any residual fertilizer left over from the cotton crop. A green crop, particularly a legume grown and ploughed-in before the cotton enables the land to be ploughed early in the season. This adds some nitrogen to the soil and improves the structure and water holding capacity.
GENUITY BOLLGARD II COTTON
This variety of cotton provides a broad spectrum seasonal long control of worm pests. This allows farmers to reduce and even eliminate sprays for worm pests therefore there is a build-up of beneficial insects as there are fewer sprays on the crop. It reduces the level of pressure and damage, in-between sprays allowing the farmer to focus on other aspects of producing cotton.
ROUNDUP READY FLEX COTTON
The roundup ready variety allows for a flexible weed management program which targets a broad spectrum of weeds. This allows the farmer to spray the crop according to the weeds growing and not at the stage of the cotton. Roundup will not affect the cotton at the reproductive phase as many other chemicals do and there is less spraying to be done thus saving on labour costs.
GENUITY BOLLGARD II WITH ROUNDUP READY FLEX COTTON
This variety combines both the above. This reduces across the field as one can mix the roundup and other insecticides together. It also reduces the stress of having to spray at certain stages of development which allows for more flexibility.
New varieties are being developed all the time which may be more drought tolerant or resistant to insect pests, so anybody wanting to grow cotton should contact his local cotton advisor every year before buying the seed, for advice on the latest and best varieties for his areas.
Cotton needs Lime, as acid soils will limit yields. Soils should be above a pH of 5.7 and will grow well at a pH of 6.5 – 7.5. It is one of the few crops which can withstand a certain amount of salinity.
Table 2: General fertilizer recommendations are:
|SEED COTTON YIELD, 1 TON/HA||SEED COTTON YIELD 2.5 TONS/HA||SEED COTTON YIELD 4 TONS/HA|
The most important factor is the amount of nitrogen to apply; too little causes poor growth and poor yield, while too much, particularly in a wet season will cause very rank, dense growth, which interferes with spraying and makes harvesting difficult.
On heavy soils, all the fertilizer should be given as one dressing in the seedbed. On sandy soils, the potassium, phosphorus and 1/3 of the nitrogen is disced into the seedbed, and 2/3 of the nitrogen given as a top dressing 4 – 8 weeks after planting.
On normal soils the top dressing is given with Ammonium Nitrate but on very alkaline or saline soils, sulphate of ammonia should be used, because this is an acid fertilizer. The top dressing can be given as a single dressing or split into two given at 4 weeks and 8 weeks after planting. Top dressing to late will extend the growing season of the crop for too long.
The best time for planting cotton is from mid-October to mid-November. Crops without irrigation should be planted immediately after the first planting rain, although if there is a good soil tilth to ensure even germination can be dry planted 1 – 2 weeks before the first planting rain is expected. This is provided that the soil temperature has maintained a temperature of between 16 and 18º C or higher for more than 10 consecutive days. Even with supplementary irrigation there is no advantage in planting earlier than mid-October as wet weather in early March will hamper picking and may cause discoloration to the open bolls. Cotton should not be planted before the 10th October.
Planting can be done by hand, by seed drill or by an adapted maize planter. Seed should be planted 25 mm deep in clay soils and not more than 50 mm in sandy soils. This is shallow planting and requires a fine tilth to make sure that the seed is planted at an even depth.
The amount of seed required will depend on the method of planting, the distance between plants and the distance between rows. Seed should be ‘acid de-linted’ seed. This seed has had all the fuzz removed by a special acid process and flows easily in a seed drill: Fuzzy seed is unsuitable for using in a drill as it sticks together.
The distance between rows will depend on the equipment available on the farm for subsequent inter-row cultivations and spraying, and can vary from 750 mm to 1 000 mm.
Table 3: A guide to the distance between seeds is as follows:
|Row Spacing||Seed kg/ha|
|4 seeds every 150 mm (hand planted)||750 mm||29|
|Machine planted||1 000 mm||21|
Seedlings should be thinned out approximately 3 – 6 weeks after germination when the plants have reached a height of 15 – 20 cm with hand planted seed being thinned to one plant per station. With a machine-planted crop which has germinated before 10 November, leave one plant every 250 mm. For crops which have germinated after 10th November, leave one plant every 150 mm.
Table 4: The following table gives the plant population at different row and plant spacing’s, and the number of bolls required on each plant to give a yield of 1 650kg/ha.
|Row Spacing mm||Plant Spacing mm||Plants / ha||Bolls / plant for 1 650 kg/ha|
|750 750||150 250||88 711 53 200||5.0 8.3|
|1 000 1 000||150 250||66 700 40 000||7.0 11.7|
It is obvious that row and plant spacing makes a big difference to the number of plants per ha, and the number of bolls which have to ripen on each plant in order to achieve a good yield. One can appreciate that late planted crops need closer plant spacing because fewer bolls are required than on each plant; there are more plants, but they do not have to produce so many bolls.
Weeds are the greatest single obstacle to increased cotton yields on commercial farms. Trials which have been conducted in many areas have shown very clearly that weed competition in the first 6 – 8 weeks of the life of the cotton crop can reduce yields by 40 – 60%. Even light weed competition during the early life of the crop has a serious effect, much more so than was generally realised. The general opinion is that weeds cost the farmer between 500 and 800 kg/ha of picked cotton, which is a huge loss and more than the cost of weed control.
Weeds should be tackled by the use of three methods available to the farmer. Hand hoeing, using mechanical cultivations and preferably making the maximum use of fast operating equipment such as the gang tiller and using herbicides. Given good weather and hot dry conditions, weeds can be eradicated by hand and mechanical methods but the weather must be right and labour available at the right time. The table below gives herbicides which can be used on cotton, and of three types:
|Pre-planting herbicides||These are incorporated into the top few millimetres of the soil before the crop is planted.|
|Planting herbicides||These are incorporated into the seedbed at planting time.|
|Post emergence herbicides||These are sprayed on while the crop is growing and destroy the weeds without harming the crop.|
Table 1: Herbicides that are registered for the use on cotton
|PRODUCT||TRADE NAME||TIME OF APPLICATION||WEEDS CONTROLLED||NOTES|
|Trifluralin||Treflan Trif||Pre-planting: incorporate 50 – 100 mm immediately||Mainly monocots||Rain or irrigation is not required to activate|
|Pendimethalin||Stomp EC||At planting (pre-emergence)||Most||Not on sand. Residual effects|
|M.S.M.A.||MSMA 720 SL||Directed spray Post-emergent||Most weeds in seedling stage||May have to repeat. Do not apply after first blooms|
|Farmers should always check with their herbicide reps for advice on new herbicides for cotton.|
The main problem in growing cotton is the control of insect pests and farmers are fortunate that disease is not a major consideration. The following diseases do occur, but are not a serious problem.
BACTERIAL BLIGHT (XANTHOMONAS CAMPESTRIS PV. MALVACEARUM) OR BLACK ARM DISEASE
This causes dark green, angular water soaked marks on the stems and underside of the leaves of the plant and is sometimes called Angular Leaf Spot. On the upper side of the leaves, necrotic, angular brown spots develop. The disease is carried over from plant debris and contaminated plant seed. The seed can be treated using an acid treatment of copper oxychloride at a rate of 650gs/100kg seed. This disease is avoided by using varieties of cotton which are resistant. Debris can be ploughed in and crop rotations are important. A chemical spray can be used such as Dichlorophen at a rate of 1 – 1.5 litres/ha.
|Debris: scattered pieces of rubbish or remains. Necrotic: the death of most or all of the cells in an organ or tissue due to disease, injury.|
This is a fungal disease (Verticillium dahlia) which can live in the soil for many years. Cool weather favours the development of the disease and the plant can be infected at any stage of its growth. Symptoms are a yellowing of the leaves between the veins and at the leaf edge. The disease develops from the bottom of the plant and moves upwards. One needs to take care in controlling this disease by deep ploughing the lands, crop rotation with non-host plants, effective weed control and well-adapted varieties.
|Scouting: the action of gathering information. Tubercles: a small rounded projection or protuberance, especially on a bone or on the surface of an animal or plant.|
This is also a fungal disease (Fusarium oxysporum), and attacks the plant through wounds in the root system. Cotton plants are stunted with the leaves turning pale green to yellow and later wilt and die. The leaves fall off which normally starts at the bottom of the plant moving upwards. The roots may decay and the seedlings sometime die. One should avoid planting too deep as the longer it takes for emergence the more time the fungi has on attacking the plant.
A new variety of cotton known as Bollguard is now available which is much more resistant to the various boll worms listed below. With Bollguard it is often only necessary to give two applications of a pyrethroid spray but scouting of the growing crop is still essential, checking for any sign of pests. The main ones are described below. At the first sign of any pest the crop must be sprayed specifically for that pest. Pesticides are being modified and changing all the time, so any cotton grower must get specific instructions from his cotton adviser as to which pesticide to use for each of the pests he may get in his crop.
PINK BOLL WORM
The pink coloured larvae of a small moth. It attacks the green boll and feeds on the immature seeds. Main infestation occurs during the later stages of the crop because eggs are laid in protected places near the boll therefore insecticides are usually ineffective. Prevention is achieved by destroying all trash from the crop and having a closed season of at least 2 months.
RED BOLL WORM
Pale blue eggs turning grey prior to hatching and are laid all over the plant. Larva has rose-red arrow head markings and newly hatched larva is greyish-white. They are internal feeders on bud or bolls which attacks the growing points.
AMERICAN BOLL WORM
Glistening yellowish-white eggs, slightly smaller than the Red Boll worm. Usually found on the younger parts of the plant. Larva has dark band along back, on each side of which is a series of light and dark bands. It feeds with parts of the body exposed outside of bud or boll and is a voracious feeder of all parts of the plant.
SPINY BOLL WORM
Characteristic fleshy tubercles are seen along backs, sparse coarse hairs on all segments. It will attack buds and bolls besides tip boring.
Small, yellowish-green bugs found on the underside of leaves. Their presence is indicated by the yellowing leaves with slight curling of leaf edges.
Small green bugs found on the growing tip on the underside of leaves and are slow moving. Presence of sticky honeydew indicates heavy infestation.
RED SPIDER MITE
Tiny red dots found on the underside of leaves. Leaves mottle on upper surface of leaf later turn yellow and are shed. Fine webbing is visible on the underside of leaves on heavily infested plants.
Insects approximately 1 cm to 2 cm in length orange, red and black in colour with long stylet mouth. Feeds on seeds and stains lint of immature bolls. When attacking open bolls, no staining results.
Very small brown bugs capable of jumping with considerable vigour. Young leaves show perforations and a ragged edge. The bugs are not easy to find.
LEAF EATER CATERPILLARS
Perforation of the leaves indicate damage done by these caterpillars.
It is most important to scout the crop during the whole of the growing season. This is done by using trained scouts to patrol through the crop looking for insect eggs and larvae so that spraying can be carried out before too much damage is done.
Figure 1: Scouting Methods:
|Position of twelve plants approximately spaced at equal intervals along the diagonals in a field for boll worm egg counts.||A zig-zag path for general examination of a field.|
RED AND AMERICAN BOLLWORM
Counts of eggs should be made twice weekly from the four trueleaf stage until the bolls mature. Along each diagonal (see sketch A), at least 12 plants equally spaced from each other are examined and an egg count made. At each count, it is better to examine a new set of plants in order to prevent damage. Some difficulty may be experienced in counting the eggs of the American Bollworm, particularly by an inexperienced person. Should this prove to be the case, then a careful examination must be made of undamaged buds and bolls. The bracts must be pulled apart and the presence of the American Bollworm will be evident by the small larvae feeding on the surface of the bud or boll.
At the start of the flowering period attacks may be expected although earlier attacks are possible. Plant inspections will show the build-up of the eggs and spraying should be commenced as soon as field inspection shows that there is an average of 1.5 eggs per plant.
As soon as Red Bollworm eggs are observed on the plants by scouting methods mentioned above, spraying should commence. This is often necessary at the formation of the first flower buds, that is, about 6 weeks after germination.
To control boll worms, Cypermethrin can be used. At a preventative approach one can spray 75ml/ha mixed in 100 litres of water/ha. Cotton over 60 cm in height should have a spray rate of no less than 150ml/ha in 200 litres of water/ha.
Numbers of this insect are found by examining 50 plants at equal distances along each diagonal mentioned above. From each plant a medium-sized leaf is examined and the number of Jassid nymphs (not adults) counted on the underside of the leaf. Counts should begin when the first leaf is fully grown and continued at weekly intervals. When an average of two Jassid nymphs per leaf are found or there is a definite increase in population from field counts, one can spray with a recommended insecticide such as carbaryl at a rate of 15 – 20kg/ha.
Examine large numbers of plants along a zig-zag course (see Sketch B) across the field and record degree of attack as follows:
- None – No Aphids present
- Very light – 1 Or 2 aphids found on plants
- Light – A large family found on a few plants
- Medium – Aphids are present on numerous plants
- Heavy – Aphids are numerous on most plants and the leaves show much curling and twisting
As soon as field inspection indicates that the attack has reached the ‘light’ stage, start spraying with Dementon-S-methyl at a rate of 500ml/ha.
RED SPIDER MITE
Examine the leaves from all parts of the plants in a zig-zag course across the field. Record the degree of attack as follows:
- None – No red spider mites found
- Light – A few spider mites found on 1 or 2 leaves
- Medium – Spider mites easily found
- Heavy – Upper surface of leaf mottled yellow and on the under surface fine webbing noticed.
Spraying should commence as soon as the pest is detected in the field. Any delay will result in greater difficulties in obtaining control and will necessitate additional sprayings. Medium to heavy infestations will require 2 sprayings at 5-day intervals, and an additional spraying should be done if red spider is found in the field. Where an infestation is found in patches, these should be carefully spot-sprayed with 300ml/ha of Abamectin in 100 litres of water as a preventative measure.
It is most important to apply the correct quantities of a spray to the crop as too little will not kill all the pests and too much causes unnecessary expense and may damage the crop. The main thing is to read the instructions on the can or packet of spray very carefully so you know exactly what you are putting on to the crop.
Spraying can be done by knapsack sprayer, carried on the back of the operator, by tractor sprayer using a boom with 7 or 9 nozzles, or by aerial spraying by fixed wing aircraft or helicopter. Whichever method is used, the capacity of the spray tank will be known to the farmer. The spray itself is bought in a concentrate form and must be mixed with water before applied to the crop. The label on the tin will give the amount of the active ingredient in the spray and the amount of concentrate to put into the tank of the sprayer must be carefully calculated.
Table 2: The outputs of various spraying methods are:
|Helicopter or aircraft||40ha per hour|
|Tractor Sprayer – 7 nozzles||14ha per day|
|Tractor Sprayer – 9 nozzles||18ha per day|
|Tractor Sprayer – Mist blower||30ha per day|
|Knapsack Sprayer||2ha per day|
Points to note when spraying:
- Heavy rains soon after or during spraying means that the spraying must be repeated;
- Spraying must not be carried out whilst there is dew on the plant;
- The last three sprays should also aim at preventing a build-up of pests for the coming season;
- Towards the end of the season, when dry conditions have set in, intervals between spraying may be increased from 7 – 14 days, depending on the intensity of the infestation;
- The total number of spray applications may vary from 8 to as many as 15 per season;
- When combining insecticides, it is important to maintain the spray concentration of each individual insecticide; and
- Never use equipment that has been used for applying hormone weedkillers.
|Defoliated: remove leaves from (a tree, plant, or area of land), for agricultural purposes.|
In hot dry conditions, irrigation is essential if a cotton farmer is to obtain any crop at all. In cooler moister areas irrigation enables cotton to be planted at least 1 month earlier than dry planting and this ensures hot, sunny weather for the early development of the plants. This means that yields can be greatly increased by as much as 3 – 5 t/ha.
Soils vary in depth, in water-holding capacity and the water required by the crop will depend on the weather and the stage of crop development, so that exact amounts of irrigation will vary from farm to farm. However, the following general rules apply:
- The soil should be brought up to field capacity to the full root depth before the crop is planted. To do this on deep, dry basalt soils may require over 300 mm of irrigation water.
- Subsequent irrigations should be timed to allow 75% of the available soil water to be used up before bringing the soil back to field capacity. Remember that cotton does not like ‘wet feet’.
- Cotton can be given a certain amount of water stress (i.e. lack of water), as this causes an upright compact growth with no loss of yield. However, water stress must not be overdone. Wilting in cotton is shown by a dull greyish appearance of the leaves and at this stage the crop is slightly stressed. When the leaves become limp, the crop is severely stressed. Cotton in full cover during the flowering period will use about 50 mm of water a week during dry, sunny weather.
- Irrigation should cease when the first bolls start splitting.
Cotton is usually harvested by hand and because of this the cotton is of a very high quality with a good trade on the world market.
Picking may start when 4 bolls per plant are open. A crop reaped in 4 – 5 pickings requires no more labour than a crop picked in 2 pickings and the more often the crop is picked the less the loss will be due to fallen bolls and rain damage. Picking should be delayed in the mornings until the dew has dried off. Two pickers work on either side of a single row, use both hands to pick and separate the stained and clean cotton into separate bags.
Allow 2 ½ pickers/ha for a period of 12 – 16 weeks if the crop is going to be picked through several times during harvesting.
The cotton plant should be defoliated before a mechanical picker can harvest the cotton. Defoliation is a process by which the crop is sprayed with a chemical such as Dimethipin at a rate of 1.5 – 2.5 litres/ha. This is done to damage the leaf to allow the ease of harvesting. One must take care that all the leaves are sufficiently being covered to ensure an even coverage of chemical. This process is done when 50 – 60% of the cotton bolls are open. Defoliation normally takes 7 – 10 days to complete, depending on the prevailing weather conditions.
The picking process can start as soon as there are only a few leaves left on the plant that are not easily removed. If defoliation is done too early, there is an increase in yield loss and a reduced quality because it forces immature bolls to open.
Figure 1: Mechanical harvesting of cotton
Table 1: Output that can be expected from trained pickers:
|Bolls per kg||PRODUCTIVITY|
|175||8.5kg||7.0kg||4.0kg per reaper / hour|
|250||6.0kg||5.0kg||3.0kg per reaper / hour|
|300||5.0kg||4.0kg||2.5kg per reaper / hour|
Cotton can be picked clean and ready for baling, but where cleaning is necessary, it can be spread on wire mesh at waist height and cleaned by the pickers.
Make sure the cotton is dry when it is baled. Each bale should be square and weigh about 180 kg. Time to pack 1 bale is 25 minutes for a team of 3 men, and 15 minutes for 1 man to sew up the bale. Do not mix grades of cotton in a bale, but pack each grade separately.
All crop residues must be ploughed in, burned or otherwise destroyed completely by the following dates, so that there is no carry-over of pests from the old crop to the new crop.
1st August is the date at which all areas infested with Pink Boll worm must have been ploughed in by.
Planting of the new crop should not take place before 10th October.
|Deregulation: remove regulations or restrictions from.|
Since the deregulation, seed cotton and cotton lint can be marketed in three ways:
- Seed cotton can be sold to a ginner who gins the cotton and then sells it off to spinners and seed processors. This can be done directly by the ginner or through a marketing agent. The ginner determines the price and the farmer delivers or hands over the ownership of the cotton.
- Another option would be to contract the ginner to gin the cotton on the producer’s behalf for a predetermined fee. In this way the producer remains the sole owner of the product. The producer can then market the product himself or contract the ginner to do so or make use of a marketing agent.
- The farmer could also gin the cotton and either market the products themselves or use a marketing agent or someone else.
Grading of the cotton is done according to the South African Grading Standards. There are 4 grades for marketing cotton; Grade A, B, C and D, with A receiving the best price. If there are issues arising on delivery of the product that cannot be sorted out by the parties involved, the Quality Control Department of Cotton SA would take the role as the arbitrator. Other organisations that regulate disputes are the Liverpool Cotton Association and Bremen Cotton Exchange.
Before seed is purchased the lint is removed by a special acid process and leaves a smooth seed which can be sown by a seed drill or planter.
The seed that remains after the ginning process is called ‘Fuzz’ and is a valuable livestock feed, particularly for cattle. It is sold to farmers and food compounders and is high in both protein (D.C.P.) and Energy (T.D.N.)