Harvesting ripe cotton

Cotton varieties

On this page:

• Plant breeders rights (PBR)
• Planting
• Harvesting, processing and marketing

Seed companies continue to release cotton varieties with improved fibre qualities and resistance to disease and insects.

For information and descriptions of recommended commercially-available varieties, growers are referred to the Variety Guides which are produced annually by seed companies, Cotton Seed Distributors Ltd and Deltapine Australia Pty Ltd.

Plant breeders rights (PBR)

Some varieties are protected under the Plant Breeder's Rights Act 1994. Seed of these varieties can only be bought from the owner of the variety or an agent authorised by the owner. Trading seed without authorisation can lead to prosecution and court action for damages. Once purchased, a grower can maintain seed of a variety with PBR protection. Farmers can sell the products of a protected variety for commercial use as feed or food but cannot sell the variety for seed.

Transgenic cotton

Bollgard II^® is genetically modified cotton that contains Cry1Ac and Cry2Ab genes to provide control of Helicoverpa spp. These genes were obtained from the naturally-occurring soil bacterium Bacillus thuringiensis, which targets specificity against Lepidopteran pests such as Helicoverpa. The widespread use of this technology has facilitated a general move by the industry towards integrated pest management (IPM) and reduced reliance on broad-spectrum insecticides.

Herbicide-tolerant cotton such as the Roundup Ready^® varieties have been modified using gene technology to tolerate applications of glyphosate. Roundup Ready Flex^® cotton contains an extra gene which allows greater glyphosate tolerance compared to Roundup Ready^®. The genes used in Roundup Ready^® varieties are obtained from a naturally-occurring soil bacterium. Liberty Link, new herbicide tolerant variety is tolerant of Liberty herbicide^® which provides growers with a new mode of action and better options for weed management. Some herbicide-tolerant varieties contain both the Bollgard II^® and Roundup Ready ^®genes.

Australian cotton growers are very experienced and familiar with genetically modified (GM) cotton, which now accounts for about 90% of the cotton grown in Australia. GM cotton and best management practice has ensured the sustainability of the Australian cotton industry.

Contact your local cotton consultant, agronomist or cotton seed company for further information on Bollgard II^® cotton.
Accreditation is required before growers can grow Bollgard II^® cotton.

Variety selection strategy to aid disease management of cotton

FUSCOM, a committee of the Cotton Catchment Communities CRC, has developed a standard protocol for describing cotton cultivar resistance to fusarium wilt and verticillium wilt. The protocol is to provide growers with a quantitative measure of resistance of new and existing cotton cultivars. The disease resistance rankings are based on the survival of plants in the presence of significant disease pressure. The disease rank is a management tool to assist cotton growers in choosing the best cotton variety to plant in their environment - considering the risk for disease.

The Fusarium ranking (F. rank) is calculated from a rating comparison of plant survival and stem infection to the industry standard variety - Sicot 189.

The Verticillium resistance ranking (V. rank) is calculated from a rating comparison of plant survival and stem infection to the industry standard variety - Sicala V2.

Pooled trial results are published in the Variety Guides which are produced annually by seed companies, Cotton Seed Distributors Ltd and Deltapine Australia Pty Ltd. The number listed in brackets after the rank number indicates the number of field trials included in the determination.

Back to top

Planting

Planting time

General recommendations state that sowing cotton should not occur until minimum temperatures of 14°C at planting depth is maintained for three consecutive days.

The effect of temperature on seedling emergence

Minimum soil temperature at 10 cm °C	Seedling emergence and survival %	Days to complete emergence
10	56	29
14	73	17
18	90	5

Source: Constable and Shaw (1988)

In regions where the disease fusarium wilt is known to occur, many growers have delayed planting cotton up to 2-4 weeks than previously practiced, as a management practice to reduce the effect of cold stress on seedling emergence and development. On the Darling Downs, minimum soil temperature of greater than 17°C (at about 7 am) at planting depth for three consecutive days before planting has been widely recommended. Later plantings assist rapid germination and good seedling growth and contribute to a reduction in the development of seedling disease and fusarium wilt.

When to plant

Central Queensland

Irrigated

Optimum planting time is mid-September to October. Regional growers have adopted a planting window to cut down the time insects are exposed to chemicals (15 September to 31 October). This reduces the generations that are selected for resistance.

Dryland

Optimum planting time is November to early December. Crops can be planted from late September to late December. Crops planted in September and October reach the critical peak flowering period in December when there is a high risk of hot dry weather which can limit yield and cause early cut out. Crops planted later than mid-January are at a higher risk of frost damage.

Western Downs and Border Rivers

Late September to late November. Late October preferred.

Darling Downs and South Burnett

Irrigated

Early October to mid-November (late October preferred). Plantings do occur from late September until mid-November for irrigated crops.

Dryland

In late November for dryland crops on the Northern Downs.

Yield potential and quality are decreased by later plantings. Early plantings under cool and/or wet conditions are more susceptible to seedling diseases and sucking insect attack.

Planting Bollgard cotton

Bollgard II^® cotton have restrictions on planting dates for different regions. The purpose of a defined planting window is to limit the number of generations of Helicoverpa amigera that will be exposed to Bollgard II^® in any one season. This measure effectively restricts the selection pressure on H. armigera to develop resistance to Bollgard II^®. It is recommended that you contact your seed distributor for more information as planting dates for Bollgard II^® may vary.

Plant population

Irrigated

90,000-120,000 plants/ha or 9-12 plants/m of row.

Dryland

45,000-60,000 plants/ha (depending on row configuration) or 6-9 plants/m of row.

Approximate number seeds/kg

Seeds/kg range - 9000-13,000 seeds.

Refer to the Variety Guides produced annually by seed companies, Cotton Seed Distributors Ltd and Deltapine Australia Pty Ltd, for specific varietal seed/kg information.

Average seeding rate

Irrigated

Table 1. Average seeding rate for irrigation

Plant population/ha	Seeding rate kg/ha Emergence
	60%	80%
86,000	16.2	12.2
100,000	18.9	14.2
128,000	24.2	18.1

Dryland

6-12 kg/ha.

Seed

Acid delinted seed is available from a number of agribusiness firms. The orders are filled by Cotton Seed Distributors Ltd at Wee Waa, or from Deltapine Australia Pty Ltd at Narromine.

Germination

Minimum prescribed 70%.

Planting depth

Seed should be placed into moist soil with good seed soil contact at 50-75 mm. Avoid deep sowing.

Planting machinery

Row crop unit planters and press wheels are preferred, but combines will give satisfactory results with 87-105 cm row spacing. Press wheels are highly recommended; soft-centred type and low pressure recommended.

Seedlings usually emerge in 6-8 days, with full stand in 9-12 days, but this may be complicated by seedling disease.

Row spacing

Irrigated

Conventional solid plant - every row planted with 100 cm spacing most common.

Ultra narrow row (UNR) - planted rows spaced 18-35 cm apart.

UNR has been trialled extensively in short season irrigated cotton growing regions of southern New South Wales. UNR offers some advantages including compatibility of planting and cultivating gear with other row crops, faster canopy coverage and earliness. Trials have not proven that there is a yield increase with UNR. Disadvantages include drainage problems with shallower furrow, shoulder compaction, picking difficulties and more demanding crop management.

Dryland

Solid - every row planted, generally at 100 cm spacing.

Worth considering on the deeper, high moisture-holding soils, especially when the profile is full at planting time. This configuration has the highest yield potential but is more expensive than skip-row configurations, using more seed, fertiliser, herbicide, insecticide and defoliant, coupled with higher picking costs. Use of a ground rig for as long as possible will help reduce quantity of chemical applied and application cost.

Single skip - every third row left unplanted.

Most common configuration used for dryland production systems. It allows for ground rig application throughout the season, and provides a measure of insurance should dry conditions be encountered at a critical time. In some instances, a three-metre gap is left for tracking, rather than straddling a pair of rows. In a wet year with good growing conditions, plants can become quite tall, with a number of resultant problems associated with chemical application and picking.

Double skip - two rows planted, two left unplanted.

Generally used on soils with less water-holding capacity, or as an added risk reduction factor. Benefits are as outlined for the single skip, with an additional reduction in costs, especially picking costs. Quality of double skip cotton tends to be better. However skip-row does create more erosion, so any gains in the short-term may be offset by higher soil losses in the long-term.

Modified skip: Variation of solid plant with blocks of rows at normal spacings separated by unsown traffic corridors to facilitate more extensive use of ground rig equipment.

Narrow/wide rows

Narrow (75 cm) and wide (145 cm) rows are used on small areas in regions where stripper harvesters are available, notably in Central Queensland and northern New South Wales.

Standardisation on 100 cm is likely to be beneficial with respect to setting up boom sprays, as most commercial booms use 100 and 50 cm nozzle spacings. Narrower row spacings of 75 cm are being used in some areas now that variable spacings have been incorporated in new model cotton pickers and strippers harvesters.

Hilling up is not necessary for dryland cotton at planting, but some hilling during inter-row cultivation aids in picking.

Crop development

The rate of germination and emergence, initiation of squares and the development of flower buds to maturity is controlled primarily by temperature and this relationship is described by the term 'day degrees'. Temperature and consequent day degrees affects the actual time the plant takes to move through the various growth stages. Peak flowering generally occurs in December/January in Central Queensland and a month later on the Darling Downs.

Table 1. Growth stages of the cotton plant

Stage	Duration	Day degrees
Planting to emergence	6 - 20 days	80
Emergence to first squares	34 - 45 days	505
Square to flower	20 - 30 days	272
Flower to mature boll	40 - 80 days	750
Sowing to first open boll	102 - 175 days	1527
Sowing to crop maturity	140 - 200 days	2005

Average season day degrees:

• Dalby - 2190
• Emerald - 2986
• Goondiwindi - 2470

Heat accumulation is calculated progressively during the season to monitor crop development and progress. The higher the average temperature, the less time it takes from sowing to maturity. Cooler temperatures delay cotton development and development ceases at 12^oC. This base temperature of 12^o C is used in calculating day degrees or heat units. Day degrees can be calculated by subtracting the base temperature (12^oC) from the minimum and maximum temperatures and obtaining an average of the sums. The typical values of total day degrees are presented in table 1.

(Note: If the minimum is less than 12°C a value of zero is used)

Temperature and consequent day degrees affects the actual time the plant takes to move through the various growth stages. Peak flowering usually occurs during December to early January in Central Queensland and late January to early February on the Darling Downs.

Further information about crop development and management practices can be found on the Cotton Catchment Communities CRC website. Also see Cotton resources and contacts.

No-till planting of cotton into cereal stubble

Several Central Queensland (CQ) cotton growers have adopted the practice of planting cotton no-till into wheat stubble. In the CQ climate, which allows early maturity of both wheat and cotton, this can mean two crops are grown in one year.

In irrigated cotton, this practice has shown the following advantages:

• reduced early season helicoverpa pressure
• improved infiltration in hard-setting soils
• improved irrigation uniformity in fields with varying soil types
• reduced erosion/movement of pesticides off field.

The system however offers a number of challenges including:

• effective nitrogen management
• weed management
• waterlogging on flat fields.

Growers thinking of planting cotton into wheat stubble should discuss it with their consultant or cotton extension officer.

Irrigation of cotton

Irrigations can be scheduled using soil moisture measuring devices such as neutron moisture meters or capacitance probes (e.g. EnviroSCAN, C-probe or Diviners). Furrow irrigation is most commonly used, however sprinkler irrigation (centre pivots and lateral moves) and subsurface drip irrigation is becoming increasingly popular. Crop irrigation requirements will vary widely with districts. Examples of average irrigation requirements in Central Queensland (including pre-watering) are 6-7 ML/ha in Emerald versus 5-6 ML/ha in Callide-Dawson. For southern Queensland they vary from 4-5 ML/ha on the Darling Downs to 6-7 ML/ha for the Border Rivers and St George.

The amount of water used will depend on the efficiency of the irrigation system. Water recycling systems are present on most farms to reduce water use. Inadequate drainage of excess water will cause waterlogging and subsequent yield loss. Cotton is particularly sensitive to water stress during flowering.

The area of cotton planted under irrigation should be determined by:

• the ability to complete an irrigation cycle every 7-10 days during peak flowering of the crop
• the total amount of water available - moisture stress has a large effect on yield.

See Managing water resources for further information.

Back to top

Harvesting, processing and marketing

Defoliation

Defoliation (by artificial means) results in the abscission or shedding of foliage earlier than would have occurred naturally. It artificially prepares a crop for harvest. The term desiccation (the rapid drying and death of foliage) is often used to describe defoliation. Cotton defoliates much easier with a good boll load, and with available nitrogen all used up.

Objectives of defoliation include:

• removing or reducing the canopy to allow more efficient operation of the picker or stripper
• promoting earlier picking by evenness of ripening
• eliminating material that could stain the cotton fibres
• reducing the trash content of seed cotton
• reducing the chances of lower boll rot in rank cotton.

The type of chemicals used for defoliation depends largely on chemical cost and evironmental constraints. If chemicals are applied at high rates, excessive injury may kill tissues in the abscission zone and prevent leaf drop. Low rates may fail to initiate the defoliation process.

Crops can be safely defoliated after 60-65% open bolls. Counting the total number of open and harvestable bolls will determine the timing of defoliation. Due to its canopy, most Australian irrigated cotton is defoliated twice in order to achieve the desired level of defoliation. The first defoliation removes the top leaves, while the second removes the lower leaves.

Factors affecting successful defoliation include:

• timing of last irrigation
• nitrogen status of crop
• the type and rate of chemical defoliants used
• its application method and rate.

For more information on the use of defoliants, contact your consultant, agronomist or regional cotton extension officer.

Harvest

It is essential, especially for first-time growers, that season planning includes harvest arrangements such as contract pickers to avoid end of season problems.

Cotton is harvested with either a spindle picker or stripper harvester. Spindle pickers are preferred for handling the yield of irrigated and most dryland cotton crops.

In Central Queensland picking starts late February through to the end of April. In southern Queensland picking occurs from March to June. Picking starts when at least 80% of bolls are open if two picks are desired. One pick harvest may be more economic in most seasons.

Moisture content in the cotton determines the initial start of picking, the length of the picking day, and the uninterrupted continuation of picking until completion. Excessive moisture (greater than 12%) causes spindle wrap which leads to lower out-turns, lower quality and quantity of cotton ginned.

Processing

Ginning cotton is the process where cotton seed and the majority of foreign matter (trash) are removed from the lint. Ginning is carried out in a cotton gins, which are located in all cotton-growing regions. Seed cotton can be stored safely at moisture contents of up to 12% but wet cotton, especially cotton containing green plant material, must be processed immediately to prevent deterioration caused when cotton heats up.

The ginning process involves drying the cotton, removal of leaf trash and dirt and separating the lint from the seed. Once lint is cleaned, it is compressed into 227 kg (500lb) bales. While cotton is being baled, a sample is taken from both sides of the bale and these samples are sent to cotton classers. Cotton lint can be classed visually by hand and/or by a machine known as HVI (High Volume Instrument).

Cotton is examined for trash, colour and extraneous matter. Quality parameters include micronaire, fibre length, uniformity and fibre strength. The majority of Australian cotton is processed further in spinning mills in Asia.

Marketing

The competitive nature of the international cotton market means that there is a range of marketing alternatives for Australian cotton growers. Marketing strategies will vary from grower to grower, depending on their individual level of risk aversion, sophistication and understanding of the marketing options.

The international supply and demand for raw cotton is constantly fluctuating and, as such, cotton prices are volatile. Growers are not only at risk from the fluctuating prices but also from the relationship between the US dollar (income) and the Australian dollar (production costs).

Forward contracts are customised agreements between two parties and involve yield and quality risks by both parties. Premium graded cotton is higher than standard, while discounted prices are paid for inferior grades. There are many types of forward contracts such as fixed bale, fixed acerage and minimum price pools.

Fixed bale pool is a commitment to deliver a specified number of bales to a 'pool of bales' with a marketing organisation. Most pools have an indicative price attached and once the price is no longer achievable, the pool will be closed. The grower bears both price risk and yield risk.

Fixed acreage pool is a commitment to deliver all the cotton produced from a specified area to a 'pool of bales' in the marketing organisation. The acreage pool lessens yield or production risk but the price risk is borne by the grower.

Minimum price pool is similar to a fixed bale pool, and while the grower still bears the production risk, a certain minimum return is guaranteed. Other marketing alternatives include balance of crop pool, AUD fixed price, USD fixed price and call pools. Fixed bale and acreage pools are the most common methods of marketing cotton in Australia.

The benchmark for determining the forward price for Australian cotton is the New York Cotton Futures market. Cash prices in US dollars are determined by the prevailing daily price for May or July futures (Australian harvest period) plus a certain 'basis' to compensate for location, grade and local supply and demand conditions. The final element of the price is the prevailing exchange rate.