Overview
- What pests affect maize crops?
- Corn flea beetle
- Spotted stem borer
- Two-spotted spider mite
- Banks grass mite
- Black cutworm
- Fall armyworm
- Corn earworm
- Maize dwarf mosaic virus
- Southern corn leaf blight
- How do I manage maize pests?
- Summary
Maize is a key part of the global food market, with India producing 38,000 tonnes annually. The spotted stem borer (Chilo partellus), a single pest, has caused maize yield losses ranging from 26% to 80% across different regions of India. When combined with damage from other pests, the overall impact on maize crops is even greater. Insects and microorganisms pose a significant threat to corn production in India and worldwide, with substantial implications for the Indian economy. This article will highlight the main pests impacting corn yield in India and elsewhere, and explore solutions, including biological methods, to manage these challenges.
What pests affect maize crops?
Maize is affected by various pests, including arthropods and microorganisms. Specific pests include mites and the larvae of different moth species. The prevalence of pests varies across different geographical regions both worldwide and throughout the Indian subcontinent. Pests damage maize by feeding on its leaves, corn ears and other areas of the plant. Infections caused by microorganisms can lead to leaf wilting, resulting in stunted growth and lower yields. A single pest, like the fall armyworm, can damage 17-36% of the global maize crop, while multiple pests together can cause even greater losses, severely affecting agricultural productivity.
Corn flea beetle (Chaetocnema pulicaria)
This insect pest measures about 1.3-2.5 mm in length and is usually black with bronze, green, or blue shades. The flea beetle has strong back legs that let it jump like a flea when disturbed. It lays long white eggs in the soil, with larvae hatching after about 10 days to feed on underground plant parts. The larval stage lasts up to a month before forming a cocoon (pupa), from which adults emerge about a week later. Adult flea beetles feed on corn leaves, causing significant damage in large numbers, leading to leaf wilting, slower growth, and spreading harmful bacteria like those causing Stewart’s disease.
Spotted stem borer (Chilo partellus)
Adult spotted stem borer moths (also called spotted stalk borers) are brown and straw-coloured with a wingspan of up to 25 mm. Their larvae are creamy with red heads and have four rows of dotted stripes along their bodies. The larval stage lasts up to a month, depending on the climate. Adult moths lay eggs directly on maize leaves, and after hatching, the larvae bore into the leaf whorl to feed. Damage becomes visible as the leaves unfurl, showing pinholes in a distinct pattern and “papery windows.” Severe infestations can lead to the death of entire maize plants.
Two-spotted spider mite (Tetranychus urticae)
This arthropod is about 0.4 mm long and can be recognized by large dark spots on each side of its usually yellowish-green, translucent body. Females can lay around 100 eggs within a few days, and larvae mature in 1-4 weeks, though the life cycle duration depends on the climate. Their populations grow quickly in warm, dry conditions or where certain pesticides have been used on leaves. Some pesticides kill natural spider mite enemies, meaning they can promote infestations in the long run. This pest harms plants by sucking fluids from the leaves, causing yellowing or “stippled” patterns. In severe infestations, leaves may become completely discoloured, shriveled, and covered with webbing on their undersides.
Banks grass mite (Oligonychus pratensis)
This pest of maize resembles the two-spotted spider mite but is black or green instead of yellowish with distinct spots. Adults can survive the winter in plant debris or soil and lay eggs on maize stems and leaves of host plants. The damage they cause is similar to that of the two-spotted spider mite, including yellowing, stippling, and leaf shrivelling in severe infestations. Like the two-spotted species, the Banks grass mite can produce webbing on the underside of leaves. However, it tends to appear earlier in the growing season and is generally considered less damaging.
Black cutworm (Agrotis ipsilon)
Adult black cutworm moths have dark forewings with lighter tips and three distinct black dashes. Their wingspan can reach up to 50 mm. Females lay round, white eggs about 0.5 mm in diameter. Larvae go through six growth stages (instars), with mature larvae growing up to 46 mm long and typically appearing gray or black. The larvae damage maize leaves and stems, posing a greater threat to young plants. Damage appears as missing sections of leaves and stems. Although females prefer to lay eggs on plants other than corn, established infestations can cause severe damage.
Fall armyworm (Spodoptera frugiperda)
The fall armyworm is a moth species that damages maize crops and is considered an invasive pest of maize in India. Adult moths are usually grey-brown with a wingspan of up to 4 cm. Their larvae are typically tan, green, or black and can grow up to 4 cm long. Damage occurs during the larval stage, and they feed on maize plants at all stages of plant growth. Young larvae feed on leaves around the whorl, causing a characteristic windowing effect and small holes in the leaves. Older larvae can feed inside the whorl and directly on the corn ear. This feeding leads to defoliation, yield loss, and reduced maize quality.
Corn earworm (Helicoverpa zea)
Adult corn earworm moths are usually brownish-yellow with a wingspan of up to 45 mm. Females can lay up to 25,000 eggs during their 1-2 week lifespan. Larvae generally have black bodies but can also appear brown, pink, or yellow with small spines and can grow up to 3.8 cm long. This pest damages maize and other plants by directly feeding on plant tissue. It feeds on various plant parts, including leaves, tassels, whorls, and ears. As larvae mature, they move into the whorl and feed on the corn ear. The presence of corn earworm waste around the ear clearly indicates an infestation.
Maize dwarf mosaic virus
This virus spreads in different ways depending on the plant it infects. In maize, infection commonly occurs through corn leaf aphid feeding. The disease’s impact on plant health and crop yield varies based on the plant type and its growth stage. Generally, earlier infections cause more severe effects on plant development. Infected leaves may first show discoloured spots that develop into a characteristic mottled pattern. As the plant matures, leaves can turn more uniformly yellow, with red streaks sometimes appearing along them. Older maize plants may experience reduced ear growth as a result of infection. When infected with a combination of viruses some plants can develop maize lethal necrosis disease. Another virus called maize streak virus causes maize streak disease.
Southern corn leaf blight
This disease is caused by a fungal species called Bipolaris maydis. It mainly affects maize but can also impact other crops. Different forms of the disease cause varying symptoms, but it typically appears as yellow-green, yellow, tan, or brown spots that slowly expand and can cover the entire leaf. Severe infections may lead to leaf death. The fungus can survive through the winter in plant debris and becomes active again when conditions are favourable. Warmth and humidity are key factors that promote the spread and severity of the infection which can also cause ear rot.
How do I manage maize pests?
Maize is affected by a variety of pests, including the larvae of different moth species and microorganisms like viruses and fungi. Managing these pests requires specific control methods to effectively prevent and address infestations.
The first step in pest management is the correct identification of the pest. In addition to the descriptions listed above, farmers should seek help from agricultural advisors to ensure accurate identification before coming up with a management plan.
Monitoring
Different pests cause various symptoms, but some are common across infestations. Visible feeding damage to corn leaves and the whorl is a common sign of an infestation in a field. Yellow spots may also appear on leaves and worsen over time and can indicate the presence of microbial and insect pests. In some cases, insects can be seen actively feeding on the corn, making detection easier. White grubs in soil may also indicate an infestation. However, certain pests are harder to spot. For example, Southern corn leaf blight causes yellowing of leaves but requires microscopic examination for proper identification.
Cultural control
General cultural control methods for managing maize include removing plant debris from the growing area to reduce pests that overwinter near crops. Trap cropping can also help manage pests that prefer other plants over maize, such as the black cutworm. However, different pests may require specific approaches based on crop and environmental factors. For example, two-spotted spider mites thrive in dry conditions, while the fungus causing Southern corn leaf blight prefers humid environments. Tailoring control methods to specific issues can improve pest management effectiveness.
Biological control
These control techniques involve the use of products derived from nature to control specific pests. They are broken down into four major categories.
- Natural substances: These are typically derived from plants and can be used in sprays to repel or kill pests. For example, extracts like neem oil can protect crops by interfering with pest feeding and reproduction.
- Semiochemicals: These are messaging compounds that can be used to disrupt pest behaviour. For example, pheromones of different pest species can be used to lure pests into traps and applied to plants to prevent feeding and reproduction.
- Microbials: These are microorganisms like bacteria, fungi, and viruses that harm pests but not crops. Fungal species like Beauveria bassiana and Trichoderma viride can be used to tackle larva pests and plant fungal diseases, respectively.
- Macrobials: These are larger animals, like certain insects, that feed on or parasitize pests.
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 highlighted above and consult the CABI BioProtection Portal for identifying and applying suitable biological control products.
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 minimizing 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
Maize is an important crop in India, accounting for about 2% of global production. However, pests such as the spotted stem borer, fall armyworm, and corn flea beetle pose serious threats to yields. Effective pest control involves monitoring for bugs in corn, cultural methods, biological solutions, and chemical pesticides. New approaches emphasize eco-friendly options like biological control to promote sustainable maize farming. Ongoing research and farmer training are crucial to apply these solutions effectively and reduce crop losses.
For tailored solutions to protect your maize crops, visit the CABI BioProtection Portal. You may also find our coffee crop pest guide useful for broader pest management strategies.
