At a glance: Cotton is a vital part of the economy in many countries, especially major producers such as the United States and India. Cotton is vulnerable to pests like bollworms, aphids, and whiteflies, but biological control methods, including natural oils and bacterial species, can help manage these pests.
Overview
- What pests affect cotton?
- Cotton bollworm
- Cotton aphid
- Silverleaf whitefly
- Cotton seed bug
- Tarnished plant bugs
- Boll weevil
- Pink bollworm
- Green stink bug
- Beet armyworm
- How do I manage cotton pests?
- Summary
- FAQ
How do I manage cotton pests?
Cotton is a vital crop for the global economy. India produces 23% of the world’s cotton, while the United States is the leading exporter, with key growing regions like California’s San Joaquin Valley playing a major role. However, cotton yields and quality are threatened by many pests. This article discusses the different pests that target cotton and describes methods for reducing their impact, including the use of biological control methods.
What pests affect cotton?
Cotton is affected by a diverse range of pests, including aphids, whiteflies, plant bugs, and the larvae of moth species like bollworms. Many of these pests feed directly on cotton bolls and seeds, reducing the marketability and yield of cotton crops.
Cotton bollworm (Helicoverpa armigera)
This pest is a species of moth that can damage cotton crops during its larval phase. Adults have a wingspan of 40 mm and appear in many colours, including green-grey and yellow-orange. Larvae grow up to 40 mm long and are typically greenish or yellow-red. They feed at the base of cotton bolls, causing surface gouges and leading to boll rot.
Cotton aphid (Aphis gossypii)
This pest appears in different shades of green, grows to 2 mm, and damages plants by piercing leaves and feeding on plant fluids. Immature cotton aphids (nymphs) can be green, light-brown, or grey. Damage may include cupped leaves, leaf drop, stunted growth, and a shiny, waxy coating caused by honeydew secretions.
Silverleaf whitefly (Bemisia tabaci)
This small pest feeds on cotton crops by piercing the surface of leaves and sucking out plant tissue. Adults reach about 1.2 mm in length, are yellow with white wings, and are usually covered in a white, waxy honeydew. Honeydew and the sooty mould it attracts can reduce cotton quality and marketability.
Cotton seed bug (Oxycarenus hyalinipennis)
The cotton seed bug damages cotton plants during its nymph and adult phases by feeding on cotton seeds and bolls. Adults grow to about 4 mm, with females being larger than males. They have blackish brown bodies and heads, and their wings are translucent. Damage results in reduced plant growth and brown spotting where the pest has pierced plant tissues.
Tarnished plant bugs (Lygus lineolaris)
This pest feeds directly on young cotton plants, including squares and small bolls, by sucking out plant fluids. Adults grow to about 6.5 mm and appear in shades of green, brown, orange, and red. Symptoms of damage include boll spotting, deformation, and rotting.
Boll weevil (Anthonomus grandis)
The boll weevil is a beetle species that feeds directly on cotton flowers and buds. Adults are grey-brown with a long snout and grow to 6 mm. They lay eggs inside cotton bolls and buds. Larvae are white with brown heads and grow to 13 mm. Symptoms include puncture marks on the sides of buds, which can be covered in a sticky secretion. The Boll Weevil Eradication Program led to the elimination of this cotton insect pest from most cotton-growing regions in the United States.
Pink bollworm (Pectinophora gossypiella)
The pink bollworm is a species of moth that damages cotton plants during its larval phase. Pink bollworm moths are small and grey and can be difficult to spot. Larvae are white with brown heads and grow to about 13 mm. They burrow through bolls to feed on cotton fibre and seeds. Damage leads to stained lint, which reduces crop value.
Green stink bug (Chinavia hilaris)
Cotton is vulnerable to attack from many stink bug species, including the green stink bug. Adults are green and shield-shaped and grow to 18 mm. They pierce cotton bolls with a needle-like mouthpiece and feed on immature seeds. Feeding can introduce microbial pathogens that cause rot. Small bolls can be completely destroyed with severe infestations.
Beet armyworm (Spodoptera exigua)
This pest is a species of moth which damages cotton plants during its larval phase. Adults are brown-grey with a wingspan of up to 32 mm. Larvae range from pale to dark green and have a light stripe on each side. They grow to about 25 mm and feed on saplings as well as squares and small bolls. The damage they cause is different from bollworm attacks because it also affects nearby leaves and bracts.
How do I manage cotton pests?
Monitoring
Keep a lookout for the symptoms described above. Common symptoms include visible damage to bolls and leaves. Adult pests may be visible on plants in cases of severe infestation. A high number of adult moths can be a sign of a pest problem. Watch for stunted plant growth and rotting bolls, which are common symptoms of pests that attack boll tissue.
Cultural control
Cultural control involves using specific farming or gardening practices to lower the risk of pest infestations. Plant cotton crops at least 800m (0.5 miles) away and upwind from other host plant growing areas, such as melons and cole crops, to help prevent infestations. Planting in the early season can help ensure plants reach maturity and are more resilient by mid-late season when pest numbers become problematic. Keep growing areas free of debris and crop residues, as they can provide breeding and sheltering sites for pests. Shredding cotton plants immediately after harvesting can help to destroy pest populations and remove feeding material.
Biological control
- Natural Substances: These are typically derived from plants and can be used in sprays to repel or kill pests. For example, oils from cottonseed, peppermint, and rosemary can be used in sprays to repel pests like the beet armyworm. Products containing neem oil and azadirachtin are also effective against some cotton pests, including the cotton bollworm, cotton aphid, and pink bollworm.
- Semiochemicals: These are messaging compounds that can be used to disrupt pest behaviour. For example, pink bollworm pheromones can be used to attract and trap this pest without impacting non-target species.
- Microbials: These are microorganisms like bacteria, fungi, and viruses that harm pests but not crops. For example, the bacterial species Bacillus thuringiensis and the fungus Beauveria bassiana are effective against the larval stages of many cotton pests, including the pink bollworm and the cotton bollworm.
- Macrobials: These are larger animals, including other insects, that feed on or parasitise certain pest species, helping with pest control. For example, green lacewings can help to control the numbers of cotton pests like silverleaf whiteflies. Encouraging the growth of natural predators, such as big-eyed bugs, is another effective method of pest control.
Chemical pesticides
As a world leader in nature-based pest management knowledge implementation, CABI encourages Integrated Pest Management (IPM) as the preferred, ecologically-based approach to producing healthy crops, which allows for chemical pesticide use only as needed, and when adhering to measures that limit the exposure of people and the environment to them (see FAO, International Code of Conduct on Pesticide Management).
Before considering the use of chemical pesticides, farmers should explore all available non-chemical control solutions, such as the ones listed above. For tailored insect pest management advice, visit the CABI BioProtection Portal, where you can enter your location and pest problem to explore customised solutions.
In case chemical pesticides are considered for use, farmers should look to select lower-risk chemical pesticides which, when used as part of an IPM strategy, help manage pest problems while minimising harmful effects on human health and the environment. Agricultural advisory service providers can provide information on lower-risk chemical pesticides that are locally available and are compatible within an IPM strategy. These experts can also advise on the required personal protective equipment.
Summary
Cotton is an incredibly important crop for many economies. However, the quality and overall yield of cotton crops are threatened by a variety of pests. Fortunately, there are effective options for mitigating their impact. Careful monitoring and careful pest identification can allow you to select effective cultural and biological control methods rather than chemical insecticides. These approaches provide a targeted method to mitigate the impact of specific pests while minimising environmental harm and supporting insecticide resistance management.
We have also prepared extensive guides on dealing with pests such as tobacco beetles, red spider mites, aphids, and whiteflies.
FAQ
What are the major pests of cotton?
The impact of different cotton pests varies by region. Bollworms are particularly damaging in the United States, while in India, the silverleaf whitefly and cotton aphid cause significant damage.
What pests can destroy whole cotton fields
Cotton fields are vulnerable to attack from a large variety of pests, which vary by region. Caterpillar pests like bollworms and armyworms, as well as aphids, weevils, and silverleaf whiteflies, can all cause significant damage to cotton fields.
What are the four major cotton pests?
Bollworms, aphids, silverleaf whiteflies, and boll weevils are four significant pests, though the impact of cotton pests varies by region.
