“The corn leafhopper (Dalbulus maidis) is a widespread concern in all corn-producing regions in Brazil…”
Michele Regina Lopes da Silva is a plant protection researcher at the Institute of Rural Development of Paraná – IDR-Paraná, collaborator of the Postgraduate Program in Agronomy of UEL/IDR-Paraná.
Lopes da Silva has a degree in biological sciences, with a specialization in biology applied to health, a M.Sc. in microbiology and Ph.D. in agronomy from the State University of Londrina – UEL.
Michele Regina, researcher at IDR-Paraná
AgriBrasilis – Is the corn leafhopper problem getting worse in Brazil?
Michele Lopes da Silva – The corn leafhopper (Dalbulus maidis) is native to tropical regions, and is a cause for widespread concern in all corn farming regions in Brazil. This insect, in addition to sucking nutrients from plants, excretes a sugary substance that attracts other insects and encourages the growth of sooty mold [a dark-colored fungus], damaging photosynthesis. When the leafhopper eats, it can transmit pathogens responsible for the Corn Stunt Disease Complex.
Also, the African leafhopper Leptodelphax maculigera was reported in Brazil in 2022, in the State of Goiás, and is already present in the Southern States of the country. This insect is a potential vector of Corn Stunt diseases because, although studies to prove transmission are still needed, pathogens from this complex have already been genetically detected in L. maculigera. Unlike D. maidis, this leafhopper feeds on various grass and leguminous plants, which could theoretically reduce the transmission of pathogens to corn.
“The absence of “green bridges” and the synchronization of spraying would result in better control of leafhopper populations”
AgriBrasilis – How is this pest monitored and controlled?
Michele Lopes da Silva – There is no curative control for Corn Stunt diseases, that is, it is necessary to focus on prevention through Integrated Management. Specific actions, such as only the application of insecticides, proved to be inefficient in previous seasons.
The basis of management is the choice of seeds from tolerant hybrids, generally of tropical genetic origin, which must receive seed treatment before sowing. Then, about a week after the plant emerges, spraying should be carried out with a chemical insecticide, aiming to kill contaminated insects that are arriving in the crop. The next application should be of a biological insecticide, to target insects that did not die from the first pesticide spraying and to preserve natural enemies of leafhoppers and other corn pests. Farmers have reported that the best time to apply this type of insecticide is at night.
Spraying must be alternated with different chemical active ingredients and between chemical and biological, until the plant reaches the V8 stage, around 40 days old. After that, spraying should only be carried out if a very high population of corn leafhoppers and darkening of the leaves, caused by sooty mold, are observed.
The critical period of protection for the corn plant is from emergence to the V8 stage and the younger the plant is contaminated, the greater the losses observed in the reproductive phase. After the V8 stage, leafhoppers continue to be observed in crops, but tend to migrate to other crops, looking for younger plants for food and reproduction.
It is necessary to carry out a good harvest, aiming not to perpetuate pathogens and leafhoppers in the field. Proper harvesting avoids spontaneous corn plants [“tigueras”], which are reservoirs of pathogens and insects.
Another important thing is to respect the regions’ sowing periods, as crops at different stages of development generate “green bridges” that also serve as a reservoir for pathogens and leafhoppers.
The ideal management would be through the union of neighboring farmers, who make up a microbasin. Farmers should synchronize their actions to reduce losses from Corn Stunt. The absence of “green bridges” and the synchronization of spraying would result in a better control of leafhopper populations.
Monitoring has been carried out using traps. Data on the number of leafhoppers captured and their infectivity with Corn Stunt pathogens make up the bulletins and alerts.
Management costs vary according to the products, but investment in hybrids that are less susceptible to diseases and in biological insecticides is advantageous for succession crops. Although the cost of biological insecticides may be slightly higher, they represent an investment for the next crops in succession.
We have recommended reinforcing seed treatment and 4 – 5 insecticide applications, according to the insect population. Application of biological insecticides after the V8 stage can help reduce the population of infected leafhoppers, which migrate to other crops.
SOURCE: IDR-Paraná
AgriBrasilis – What diseases are transmitted by this insect, and what are the damages and losses caused?
Michele Lopes da Silva – The Corn Stunt Complex is composed of systemic diseases, which affect the physiology, nutrition, development, and production of corn.
The leafhopper transmits the bacteria ‘Candidatus Phytoplasma asteris‘ (Pale stunted-Corn stunt spiroplasma), Spiroplasma kunkelii (Red stunted-Maize bushy stunt phytoplasma) and the viruses Maize “Rayado Fino” Virus – MRFV and Maize Striate Mosaic Virus – MSMV (Corn Striated Mosaic).
Damages can only be estimated, because environmental factors such as frost and drought occur simultaneously with the Corn Stunt Complex. Therefore, it is not possible to associate losses solely with diseases transmitted by the corn leafhopper. The percentages of losses are reported by individual crops, and we can mention losses of up to 40% – 100% of production.
The occurrence of diseases that cause stem rot can worsen the effects of stunting. These can cause stem breaks and plants falling over, even in the case of less symptomatic plants.
AgriBrasilis – What are the symptoms of leafhopper infestation in crops?
Michele Lopes da Silva – The symptoms of the disease vary according to the phenological phase in which the plant was infected and the degree of resistance of the variety or hybrid. There are plants that do not show many symptoms, but show a decline in production. Plants can also present multiple pathogen infections, which makes diagnosis difficult.
Generally, the plant is completely depleted, because when the leafhopper feeds, it deposits pathogens in the phloem, which facilitates the dispersion of pathogens and the clogging of vessels, restricting the circulation of nutrients.
In the stem, the internodes shorten, leading to a reduction in the size of the plant. Leaves infected with mollicutes show yellowing or reddening that begins at the leaf apex and spreads throughout the leaf, followed by drying starting at the edges. Tillering may also occur in the leaf axils. The plant may break or fall.
In leaves infected by the MRFV virus, small chlorotic spots begin at the base and along the veins of young leaves that coalesce to form chlorotic stripes. Damage caused by the MSMV virus begins with mottled lesions at the base of the leaves, which evolve into chlorotic stripes or streaks. Cobs are reduced in size, with small, stained, loose and “shallow” grains. Multi-earing can also occur without grain filling. Cob rot is also common.
SOURCE: IDR-Paraná
AgriBrasilis – Where have the biggest losses due to leafhoppers been reported?
Michele Lopes da Silva – Previously, problems with corn stunting were reported in the North, Northeast and Central-West regions of Brazil. Losses are now reported in all corn farming regions and each year outbreaks occur in different locations, probably due to changes in environmental and management conditions, which influence leafhopper populations.
Worse losses are being reported every year in all corn-farming regions in the country. The leafhopper is well adapted, and environmental changes and the lack of correct management have favored insect populations.
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