Overview:
- What are corn leafhoppers?
- What is the impact of corn leafhoppers?
- How do I know if I have a corn leafhopper problem?
- How do I get rid of corn leafhoppers?
- Summary
The corn leafhopper is a small insect pest that causes significant damage to corn crops, particularly in Brazil. It is prevalent across North and South America and have also been identified in Africa and Asia. This pest primarily damages corn by transmitting diseases that stunt corn growth, leading to significant crop and yield loss causing substantial economic consequences.
In this article, we provide an overview of the corn leafhopper, including the damage it causes, how to identify it, and effective methods to monitor and control it.
What are corn leafhoppers?
The corn leafhopper (Dalbulus maidis) is a sucking insect that affects corn crops. Adults are tan or light-yellow in colour, about 0.3 cm long, and have two distinctive dark spots on their heads, which are only visible by microscope (see image above). They can move rapidly and fly for several kilometres at a time. This means these insects can easily access and subsequently threaten maize crops across vast areas.
Life cycle
Corn leafhopper eggs are 1 mm long yellow cylinders with rounded ends that the female lays directly into the central vein of host plant leaves (see image below). This location makes eggs more difficult to spot than those of other pests. After 4-10 days, the eggs hatch, and corn leafhopper nymphs begin feeding on plant fluids. They progress through five developmental stages (referred to as instars) before becoming mature adults. This process takes roughly 2 weeks. Adult males live for about 80 days, while females have a lifespan of about one month in which they lay up to 600 eggs. These pests overwinter in other crops, such as alfalfa and grasses, before searching for corn crops in the early season.
Like many other insects, the corn leafhopper has a faster lifecycle in warm seasons and climates than in cold ones. This means this pest can produce more generations per year in warmer conditions.
What is the impact of corn leafhoppers?
The corn leafhopper damages plants by feeding on plant fluids within the corn whorl (the spiral pattern of leaves that you see in the center of a young corn plant). Specifically, it does this through xylem ingestion, where the pest consumes water and minerals from the plant, and phloem ingestion, where it consumes nutrients and sugars. This pest also releases sticky honeydew onto leaves, where black sooty mould often grows. This can reduce the plant’s ability to generate food via photosynthesis. However, the most significant impact of the corn leafhopper on plant and crop health is through disease transmission.
The corn leafhopper transmits the following pathogens:
- Corn stunt spiroplasma (CSS) caused by the bacteria Spiroplasma kunkelii, which causes corn stunt (see image below)
- Maize bushy stunt phytoplasma (MBSP), another bacteria which causes corn stunt as well
- Maize rayado fino virus, which causes a disease called maize fine stripe
The disease transmitted by this pest contributes more to crop yield loss than their direct feeding behaviour. Yield loss can be particularly severe when young plants become infected with one of these pathogens.
How do I know if I have a corn leafhopper problem?
Corn leafhopper eggs are difficult to notice without experience and knowledge of the pest’s life cycle. In fields where adult corn leafhoppers are present, the crops are always infected with at least one of the diseases mentioned above. This means that noticing the presence of adults can already indicate a problem. Damage caused by diseases leads to several symptoms that become more obvious as the growing season progresses.
Infected corn can have:
- Smaller grain and ear sizes and yield lower grain numbers.
- Leaves will be smaller and discoloured, appearing pale, yellow, or reddish.
The appearance and severity of symptoms vary depending on the strain and age of the affected plant and the number of infected corn leafhopper adults in the area.
How do I get rid of corn leafhoppers?
Despite their devastating impact on corn crops, the corn leafhopper can be managed in a variety of ways, including a combination of monitoring, cultural and biological control methods.
Monitoring
Monitoring can be performed by examining plant cartridges for insects or by using yellow sticky traps. Plant cartridges are pre-packaged units with seeds, soil, and nutrients that simplify growing plants by providing everything needed for cultivation. Traps can be used early after seeding to help identify when corn leafhoppers arrive, allowing farmers to take action early and prevent a larger infestation.
Cultural control
Cultural control involves using farming practices and techniques to prevent or reduce pest problems.
Early seeding
The number of corn leafhoppers increases as the growing season progresses. Planting seeds early can allow plants to reach a more mature stage earlier in the season, making them more resilient to damage by corn leafhoppers.
Remove volunteer corn
Volunteer corn is grown unintentionally, often due to kernels left over from harvest. This corn can act as a host for the corn leafhopper, meaning that it can survive longer into the season. Eliminating volunteer corn plants and having a corn-free period during the winter can help reduce the number of corn leafhoppers.
Crop rotation
Since the corn leafhopper primarily affects corn, planting different non-host crops in a field in alternate seasons can reduce their numbers.
Biological control
Biological control methods use pest solutions derived from nature, which provide a more environmentally friendly alternative to conventional chemical pesticides. We distinguish four categories of biological pest solutions: macrobials, microbials, semiochemicals, and natural substances.
Natural substances
These are compounds derived from natural sources like plants that can directly kill pests. Azadirachtin, a compound derived from the seed of the neem tree, is toxic to corn leafhoppers and can prevent them from feeding and reproducing. Extracts from the Mexican prickly poppy plant are also effective against this pest.
Microbials
These are microorganisms such as bacteria, fungi, and viruses that infect and kill pests. Corn leafhopper larvae are notably vulnerable to different strains of Pseudomonas bacteria and to a fungus called Beauveria bassiana. These microbes cause lethal infections in various insects. For example, B. bassiana colonises the insect bloodstream and spreads throughout its body, producing toxins and draining the insect of nutrients, eventually killing it.
Chemical pesticides
These chemicals can be used to control corn leafhopper numbers however they are ineffective at stopping the spread of diseases carried by these pests. Furthermore, chemical pesticides often kill beneficial insects and lead to a loss of biodiversity. They also pose a health risk to humans. They can be used as a last resort, and to find suitable options, speak to your local agricultural advice service.
Research
By searching on Google Scholar you can find many research papers on the corn leafhopper, including those from an Oxford Academic journal. A paper from 2022 studied the resistance of some corn hybrids (strains) to the corn leafhopper. They looked at corn leafhopper probing behaviour, which is how this pest finds a suitable part of the plant to eat. They measured the behaviour of D. maidis insects using Electrical Penetration Graph technology, which produces a different waveform (pattern) depending on how the pest interacts with the plant. They found that the corn leafhopper access maize hybrids differently depending on the strain. Some hybrids changed the time the pest spent performing phloem conditioning (preparing the phloem for ingestion). This included changes in waveform duration and the number of waveform events. They analysed their data using a statistical analysis called a fisher LSD test. Studies like these allow for the development of corn plant strains that resist the damage caused by the corn leafhopper.
Summary
The corn leafhopper is a significant pest of corn crops, causing extensive damage by transmitting pathogens. This pest is widespread in the Americas and poses a substantial problem to corn crops in Brazil. The corn leafhopper can be identified by its tan or light-yellow colour and dark spots on its head. Dealing with it effectively and sustainably requires integrated pest management, including monitoring techniques, such as yellow sticky traps, and cultural practices like early seeding, removing volunteer corn, and crop rotation. Biological controls, including natural substances and microbials, also help mitigate the impact of the corn leafhopper. While chemical pesticides can reduce their numbers, they are less effective in preventing disease spread, can harm beneficial insects and human health and should be used when other options have been trialled first.
For more information on environmentally friendly ways to combat the corn leafhopper, visit the CABI BioProtection Portal. To discover control methods for other pests, consider visiting our resource page, which provides dedicated articles on many common pest species.
