Cotton

Question 1

Background information on Cotton

Answer 1

300 million ha of cotton (2% of total cropped land)

IPM largely developed in cotton agroecosystems because of over reliance on chemicals

Question 2

How much insecticides per year are used on cotton and why?

Answer 2

25% of global insecticide use applied to cotton

• high value cash crop
• attacked by pest complexes
• not consumed
• grown in areas favourable for pest species

Question 3

Describe the biology of the cotton plant

Answer 3

Small trees/shrubs in genus Gossypium
Plant family Malvaceae (includes okra/hibiscus)
Immature flower buds (squares) blossom and become boils that have long (1-6cm) white seed hairs (lint)
Lint is spun for cotton, stalk residues are ploughed or destroyed, boll husks used to feed cattle and oil from seed is processed for industrial use

Question 4

Where did cotton originate, when and which current countries is it found?

Answer 4

Found in both old and new world from 5,000bc
Largely a tropical or sub-tropical crop that requires a lot of sunshine and water
Leading production areas comprise India, Pakistan, China, Brazil, USA, Egypt, Uzebkistan and Turkey

Question 5

Describe the growth of the cotton plant

Answer 5

Plant Establishment - From planting to appearance of first flower but (~50 days in ideal conditions)
Fruit Formation and Maturation - From appearance of first square through to first boil opening (~30 days)
Boll Formation and Maturation - Starts about 80 days (about 25 days for maturation under ideal conditions)

Question 6

Describe cotton yields worldwide

Answer 6

Average is 1.6 tonnes/ha
Varies by about 10 fold globally (0.5t/ha in many African countries to 5t/ha in Israel)
China (worlds largest producer) averages 2.8t/ha > 5 million ha

Question 7

What is the extent of cotton yield losses? What factors are important in this

Answer 7

Attacked by a range of pest species (>1,300 recorded)
Potential losses to pests are calculates >30% but actual losses are ca. 10-15%
Weeds also have the potential to cause yield loss, especially early on
Pathogens are occasionally important
Above are controlled with chemicals

Question 8

What are the key pests of cotton?

Answer 8

Pink Bollworm (Pectinophora gossypiella) - Primary Lepidopterous pest
Cotton Boll Weevil (Anthonomous grandis) - Primary Coleopterous pest
Lygus Bugs (Lygus hesperus) - Hemipterous

Question 9

What methods of pest management are used in cotton?

Answer 9

Host plant resistance
Biological control
Cultural control
Biorational compounds (pheromones, microbes etc)

Question 10

How is host plant resistance used?

Answer 10

Pilosity - resistance to weevils, bollworms, various bugs
Pigmentation - Red pigmentation affects bollworms, hemipterous pests
Transgenic crops - Expression of Bt endotoxin
Short-season crops (pest avoidance)

Question 11

Which biological controls are used?

Answer 11

Parasitoids e.g. Trichogramma
Aphid predators e.g. ladybirds
Whitefly predators e.g. lacewings

Question 12

How are cultural techniques used?

Answer 12

Crop rotations
Host-plant resistance
Planting density 
Planting dates
Phytosanitation
Boll weevils overwinter in broad leaved litter so avoid these areas

Question 13

How are biorationale techniques used?

Answer 13

Pheromones - especially for mating disruption of Lepidopterous pests
Nucleopolyhedrosis viruses (Lepidoptera)
Bt sprays (Lepidoptera and Coleoptera)

Question 14

Case study Peru

Answer 14

Canete Valley, Peru: 22,000 ha cultivated land planted with cotton in 1920s
After WW2 extensive DDT, BHC, and Toxaphene used as blanket sprays
1949-1954: yields increased by 50%
1955: resistance in aphids to BHC, bollworm resistance to DDT, whitefly outbreaks begin, more boll weevils
1955-1960: Spraying increases to every 3 days, production system becomes uneconomic
1960s onwards: Perennial planting banned, Trichogramma insectaries established, switch to nicotine sulfate sprays, organochlorides no longer used
1965 onwards: Yields begin to increase, number of applications declines substantially to ~2 per crop

Question 15

Case study China

Answer 15

1950-1970s: excessive use of organochlorides and organophosphates
Mid 1970s onwards: IPM because of resurgence, resistance, environmental contamination etc.
Many IPM programmes focused on the use of biological control agents and more recently on Bt crops
1997: introduction of Bt crops
2010: 69% of cotton grown in China was Bt cotton
Income for farmers doubled due to yield increases and 60% reduction in insecticide applications

Question 16

What biocontrol methods are used in China?

Answer 16

> 500 predators and parasitoids recorded in Chinese cotton fields (as well as various pathogens)

• Trichogramma (mass produced for field release) - reduce bollworms by up to 60%
• Microplitus (larval parasite of Lepidoptera) - mass reared and can provide 60-70% control of bollworms
• Predatory mites for spider mite control
• Bt and NPV applications for Lepidoptera

Question 17

Case Study Egypt

Answer 17

Egypt produces about 1/5th of all African production with average yields of 2.4 t/ha (substantially abouve African average)
Cultivated extensively under irrigation along the Nile
Primary pest management strategies include: NPVs, mating disruption of pink bollworm, School holiday timing for egg collection (cultural)

Question 18

Case study India

Answer 18

Yield of around 1 t/ha
India is the worlds 3rd largest producer of
cotton
Important pests include bollworms, aphids, whitefly, jassids
Historically control has been based on insecticide sprays (pyrethroids and organophosphates in last 30 years)
More recently commerical planting of Br crops began in 2002 following near collapse of cotton production due to overuse of pyrethroids an bollworm resistance
1990s: Indian farmer spending >40% of production crops on insecticides (15-30 applications per crop)
>50% of insecticides used in India were applied to cotton
2011: >10 million ha Bt cotton planted
Transformed from an importer to an exporter of cotton
Yield increases went from 300kg/ha to 500kg/ha
Insecticide use declined from >9,000 tonnes to 200

Question 19

Case study Uzebkistan

Answer 19

4th largest producer in the worlds (2.4t/ha)
Biocontrol started in 1970s as part of USSR focusing on parasitoid braconid wasps, Trichogramma and Chrysoperla (for Hemiptera)
Since break up of USSR biocontrol has declined and pesticides increases

Question 20

Case study US

Answer 20

Second biggest producer
Major problem with Boll weevil
Used DDT after WW2, imported red fire ants, used pheromones and wide insecticide treatmenrs
Bt crops have helped eliminate boll weevils
Crop rotations
At present there is an eradication programme in southern USA

Question 21

Describe the boll weevil

Answer 21

Adults very small (4-7mm) covered with small hairlike scales
Eggs hatch ~5 days, larvae feed for 2 weeks before pupating
Pupation lasts a week, adults emerge from the boll in which they developed by chewing their way out
Boll weevils can mature from egg to adult in less than 20 days, as many as 7 generations can mature in one year

Question 22

Where and to what is the only insect monument in the world found?

Answer 22

Enterprise, Alabama
Boll weevil monument
Built in 1919 to commemorate the economic diversification that was required after boll weevils devastated cotton crops, the only local product