Overview
- What pests and diseases affect chilli pepper crops?
- Bacterial leaf spot
- Western flower thrips
- Green peach aphids
- Cucumber mosaic virus
- Tobacco mosaic virus
- Alfalfa mosaic virus
- Root knot nematode
- Verticillium wilt
- Two-spotted spider mite
- Powdery mildew
- Root rot
- How do I manage chilli pepper pests and diseases?
- Summary
Chilli pepper crops play a vital role in the economy of many countries and are estimated to be a USD 1.3 billion market worldwide. Pests and diseases can have a significant impact on chilli pepper quality and yield, causing economic damage. This article covers some of the most damaging pests and chilli pepper plant diseases and offers solutions to tackling these threats, including biological approaches.
What pests and diseases affect chilli pepper crops?
Chilli peppers are vulnerable to attack from a wide variety of pests, including thrips, aphids, and spider mites. However, significant damage can occur due to infection with different microbes, including viruses, many of which are transferred between plants by aphids. Damage caused by chilli pepper pests and diseases can lead to severe losses in yield. Symptoms often appear as discolouration of leaves, though specific pests attack different areas of chilli pepper plants, such as leaves, roots, and internal sites.
Bacterial leaf spot (Xanthomonas vesicatoria)
Bacterial leaf spot is a plant disease caused by the bacterial species Xanthomonas vesicatoria. It spreads through seeds from infected parent plants. Symptoms include dark, indented spots on the upper surfaces of leaves and scab-like lesions on the lower surfaces. Affected chilli pepper plants may also develop dark spots on their fruit. In severe cases, leaves wilt and fall off, and the fruit rots, significantly reducing yield.
Western flower thrips (Frankliniella occidentalis)
This species of thrips, also known as the onion thrips, feeds on chilli pepper plants during two early developmental stages. Adult western flower thrips are slender, about 1.5 mm long, and yellow-brown, while nymphs are lighter in colour. Nymphs damage plants by slashing leaf tissue and feeding on the fluids. Affected leaves may appear stippled, curled, with a silver appearance, or covered with black thrips excrement. Much of the damage caused by western flower thrips results from the transmission of the tomato spotted wilt virus.
Green peach aphids (Myzus persicae)
Aphids are small, soft-bodied insects, usually green, and are easily recognised by a pair of long tubes (called cornicles) protruding from their lower backs. Adults are typically 1 to 2 mm long and harm plants by piercing leaves and stems to feed on plant sap. Feeding can lead to small black spots, stunted growth, and, in severe infestations, even plant death. Additionally, aphids produce a sticky substance called honeydew that coats plant surfaces and attracts ants. Aphids also transfer a number of serious plant-damaging viruses.
Cucumber mosaic virus (cucumber mosaic)
This virus has a wide host range, including chilli peppers. It produces a characteristic pattern of lighter and darker green areas on plant leaves, known as a mosaic. Damage can appear as stunted pepper leaf growth and reduced plant growth. Aphids commonly transmit this virus.
Tobacco mosaic virus (tobacco mosaic)
This virus also causes a distinctive mosaic pattern on chilli pepper leaves and can be spread by aphids. However, unlike the cucumber mosaic virus, it is also commonly spread through mechanical means, meaning farmers and gardeners can spread it by directly handling plants infected with this virus. Although infected plants eventually die, the fruit typically remains unaffected and is safe to eat.
Alfalfa mosaic virus (alfalfa yellow spot)
This virus is transmitted through the feeding activity of aphids. It causes a characteristic white and yellow mosaic pattern on the leaves of pepper plants. Unlike cucumber and tobacco mosaic viruses, aphids infected with alfalfa mosaic virus can only transmit it for a few hours after becoming infected. The risk of infection increases when peppers are grown near areas where alfalfa is cultivated.
Root knot nematode (Meloidogyne spp.)
These are tiny worms that live in the soil and within the root systems of host plants. They feed on the roots and cause characteristic swellings, known as galls. Above ground, the damage resembles other types of root problems, with symptoms such as leaf yellowing and wilting. Damage to the root system makes affected plants more vulnerable to drought stress and can also make them appear more susceptible compared to healthy plants.
Verticillium wilt (Verticillium dahliae)
This disease is caused by the fungus Verticillium dahliae, which infects plants and blocks the vessels responsible for water transport. As a result, affected plants wilt, weaken, and eventually collapse. The infection can spread between plants, making it a serious threat in gardens and fields. Internally, the plant’s vascular tissue may appear discoloured or darkened with rot, indicating severe damage.
Two-spotted spider mite (Tetranychus urticae)
These pests are a type of spider mite that can attack chilli pepper plants. Specifically, the two-spotted spider mite feeds on a wide range of plants, including chilli peppers. They are small, about 0.5 mm long, and usually orange-yellow with a dark spot on each side of their body. They use their mouthparts to pierce the undersides of leaves and feed on plant fluids. The damage they cause often appears as small yellow spots or a bronzing of the leaves. In cases of heavy infestation, webbing may also be visible.
Powdery mildew (Leveillula taurica)
Powdery mildew is a fungal infection caused by the species Leveillula taurica. The infection is more likely to spread in warm, wet conditions, and is more commonly found on older leaves when the plant is closer to fruiting. It appears as patchy white areas on the surface of leaves. The affected leaves eventually wilt and drop off. The loss of leaves can leave chilli peppers exposed directly to sunlight, which can be damaging.
Root rot (Phytophthora capsici)
Phytophthora root rot is a disease affecting chilli pepper plants, caused by the pathogen Phytophthora capsici. It develops in wet soil and can appear as water-soaked lesions on stems. In affected chilli pepper plants, the leaves turn yellow, wilt, and may resemble chilli leaf curl before dropping off. Severe infections cause root collapse, killing the plant.
How do I manage chilli pepper pests and diseases?
Monitoring
Keep an eye out for the symptoms mentioned above. Wilting and discolouration of leaves are the most common symptoms associated with these issues. In cases of severe infestations, you may also notice large numbers of adult insects, and if aphids are present, ants may be visible as well.
Cultural control
Cultural pest control involves using specific farming or gardening practices to lower the risk of pest infestations or the development of plant diseases. The appropriate cultural control method to use depends on the type of pest. For example, the microbes causing bacterial spot disease and powdery mildew thrive in wet environments. This means ensuring there is proper drainage and not overwatering plants is essential. On the other hand, two-spotted spider mites thrive in hot, dry conditions, so ensuring plants receive sufficient water can be crucial in combating them.
Biological control
- Natural Substances: These are typically derived from plants and can be used in sprays to repel or kill pests. For example, Azadirachtin is an extract from the neem plant and is effective against many pests, including western flower thrips.
- Semiochemicals: These are messaging compounds that can be used to disrupt pest behaviour.
- Microbials: These are microorganisms like bacteria, fungi, and viruses that harm pests but not crops. For example, viruses can be used to tackle bacterial infections, including bacterial leaf spot.
- Macrobials: These are larger animals, like certain insects, that feed on or parasitise pests. For example, Amblyseius andersoni is a predatory mite species that can help control the numbers of two-spotted spider mites.
Chemical Pesticides
Before considering the use of chemical control methods, such as pesticides, farmers should explore all available non-chemical control measures. These might include cultural practices like handpicking pests such as caterpillars, removing diseased plants, using resistant crop varieties, applying crop rotation and consulting the CABI BioProtection Portal for identifying and applying suitable biological control products (macrobials, natural substances and semiochemicals).
Summary
Chilli pepper crops face serious threats from a variety of pests and diseases, which can significantly impact yield and quality. Effective management involves careful monitoring, cultural practices, and biological control methods, with chemical pesticides as a last resort. By adopting integrated pest management strategies, farmers can protect their crops and support the global chilli pepper market.
The CABI BioProtection Portal offers various pest management strategies and allows you to tailor searches based on a specific fruit, such as mango, or a pest, like the aphids.
