How to effectively control the corn leafhopper

The presence of tiguera plants, which provide shelter and food for the insect during the off-season and soybean cultivation period, are among the factors that help explain the higher incidence. Seed treatment with neonicotinoid insecticides, associated with other integrated and preventive strategies, has shown good results in managing this pest.

23.03.2022 | 14:51 (UTC -3)

The presence of tiguera plants, which provide shelter and food for the insect during the off-season and soybean cultivation period are among the factors which help to explain the higher incidence. Seed treatment with neonicotinoid insecticides, associated with other integrated strategies and preventive measures, has shown good results in the management of this pest.

The intensification of corn cultivation in the off-season and irrigated systems broke the planting seasonality, providing greater pressure from pests and diseases specific, with crop exposure throughout the year in the field. In addition to this, other factors such as conditions favorable climate, high temperatures and mild winters have favored the multiplication of insects. Among the phytosanitary problems of the crop of corn, the corn leafhopper Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) has increased substantially in frequency in recent years, requiring control strategies depending on losses provoked.

One of the possible factors that has led to the increase in the corn leafhopper, mainly in the Central Region of Brazil, is the presence of tigueras corn plants during the off-season and soybean cultivation, as these volunteer plants are the main hosts of the plague and the diseases transmitted by it. Due to the adoption of technology resistance to herbicides present in most available materials on the market, these corn plants are not properly controlled in cultivation of soybeans, serving as food, shelter and a source of reproduction for several pest insects. Increased food supply during the off-season and soybean cultivation provides the maintenance of the leafhopper D. maidis at the environment, favoring the multiplication and maintenance of plants infected, with viruses and stunting.

Area comprising tiguera corn in the off-season. Source of food and multiplication for Dalbus maidis.
Area comprising tiguera corn in the off-season. Source of food and multiplication for Dalbus maidis.

The maintenance of the pest in the environment during off-season and soybean cultivation has generated high population densities in initial phase of corn crop development, period of greatest susceptibility to pest attack with high losses to producers.

The adults of D. maidis they measure approximately 4 mm in length and less than 1 mm in width. Although the predominant color is straw, the abdomen has black spots, which may be greater in individuals developed in climates with temperatures pleasant. On the head there are two black spots twice the diameter of the bones. ocelli. They have two rows of spines on their tibias. later (Oliveira et al., 2003, Waquil, 2004). During adulthood, these insects can be easily visualized inside the corn plant cartridge. The establishment occurs in the initial phase of culture development, but is capable of maintain high populations during all stages of corn development. A The average longevity of adults is 16,3 days for males and 42,1 days for males. females (Marín 1987). At the However, this period can reach 106 days in warmer temperature conditions. lows (Tsai, 1988).

Presence of tiguera corn in soybean cultivation. Favoring the multiplication of the pest and the maintenance of infected plants, with viruses and stunting. 
Presence of tiguera corn in soybean cultivation. Favoring pest multiplication and maintenance of infected plants, with viruses and stunting. 

Females lay eggs in a singly, in pairs or in groups of five to six eggs on the leaf blade or on the adaxial of the leaves, preferably in the basal half of the first leaves of young plants. The posture is endophytic, occurring within the midrib tissue of plant leaves. Each female deposits approximately 14 eggs per day, which can be deposited during the egg cycle. life up to  611 eggs. The eggs are translucent, shaped like a banana and measuring less than 1mm x 0,2mm and are easy to observe with the corn leaf against the light. After seven to ten days, if become milky. The biology of the leafhopper is directly affected by temperature. Under mild temperature conditions, eggs do not hatch. However, when incubated at temperatures above 20ºC, hatching occurs. normal for nymphs (Marín 1987).

Adults of the leafhopper Dalbulus maidis on a corn plant.
Adults of the leafhopper Dalbulus maidis on a corn plant.

During the nymph stage they go through five instars, which last around 15 days. Nymphs tend to remain static, feeding in the leaf, and only move if they are disturbed (Oliveira et al., 2003, Waquil, 2004). The nymph stage to Adult formation generally occurs between 20 days and 25 days, which is period influenced by ambient temperature.

The cigarette D. maidis has few hosts, with genus-restricted multiplication Zea. There are reports from other hosts, such as sugar cane, sorghum and some species of weeds, such as crow's foot grass (Eleusine indicates) and Grass mattress (Digitaria horizontalis) (Oliveira et al., 2016). In addition to some alternative hosts for D. maidis, species from the Poaceae family, such as colonial grass (Panicum maximum), marmalade grass (Brachiaria plantaginea) it's at Brachiaria decumbens can be infected by phytoplasmas (Hass, 2010), however, according to Sabato et al. (2015) a better assessment of the importance epidemiology of these plant species in the perpetuation and dissemination of this pathogen in corn crops.

Corn plant with Rayado Fino (Maize Rayado Fino Virus – MRFV)
Corn plant with Rayado Fino (Maize Rayado Fino Virus – MRFV)

The cigarette D. maidis is a wide-ranging insect occurrence, with presence in both crops in the summer harvest as well as in the off-season. Move within and between corn crops and in seedlings. The cigarette D. maidis is considered an initial pest in corn, since occurs in corn seedlings shortly after crop emergence, being from other corn crops (Oliveira et al., 2013a). Throughout the corn cycle, the population of this insect vector increases from the maize stages initial stages of development until flowering of plants, depending on the production of new generations of insects, and the continuous entry of more adult leafhoppers, especially when there is corn at later stages in the surroundings (Oliveira et al., 2015b). In infested areas, leafhoppers can be easily observed, feeding, preferably in the region of the corn plant cartridge (Vianna et al., 2002; Waquil, 2004).

Corn Plant with Pale Stunting
Corn Plant with Pale Stunting

Although the leafhopper D. maidis may cause direct damage through the suction of sap in corn plants, compromising the plant development, and especially the root system, this species is most important due to its ability to transmit persistently and propagates the corn stripe virus (Maize rayado Fino virus –MRFV) and two mollicutes, associated with stunting Spiroplasma kunkelii it's the maize bushy stunt phytoplasma (MBS-phytoplasma), causal agents, respectively, of corn diseases called pale stunt and red stunting (Sabato et al., 2015). Mollicutes are responsible for infections and tissue clogging of the phloem. The growing importance of the complex of stunts found in recent years, in late-season and off-season corn crops, it is related directly to the increase in the population of the vector insect, the leafhopper D. maidis.

The causal agents of Stuntings are acquired by the leafhopper when they feed on plants. sick corn. These microorganisms multiply in leafhoppers (insect vector) and are transmitted to young and healthy corn seedlings, when the leafhoppers migrate from mature crops to newly established ones. The leafhoppers infected plants can transmit phytopathogens to healthy plants for a relatively short feeding time, approximately one hour (Vianna et al., 2002; Waquil, 2004; Oliveira & Oliveira, 2010). The transmission of phytopathogens, occurs in the initial phase of corn crop development, phase in which the plant has a smaller stem diameter, allowing the leafhopper D. maidis be able to achieve the sap-conducting vessels (phloem) with the style. As a result of infections In phloem tissues, there is less plant development and weakening of the culms, which may result in the plants falling due to wind action.

Fine streaking, characteristic of chlorotic spots, in the form of a fine stripe.
Fine streaking, characteristic of chlorotic spots, in the form of a fine stripe.

The symptoms of Red Stunting are characterized by discoloration and reddening of the margin and apex of the sheets. In severe infestations, the entire leaf blade may present characteristic typical of stunting. It is also possible to check the profile of plants, either in the leaf axils or at the base of the plant and the proliferation of ears, as well as a reduction in height. Symptoms of stunting are usually more visible from flowering and close to crop maturation, mainly in regions with higher temperatures (Reis et al., 2004; Sabato et al., 2002).

Corn plant with shortening of the internodes and super spike due to the presence of mollicutes that cause red and pale stunting.
Corn plant with shortening of the internodes and super spike due to the presence of mollicutes that cause red and pale stunting.

Symptoms of Pale Stunting are characterized by the presence of chlorotic or whitish bands, which extend from the base towards the apex of the leaves, and may present reddening of the lower leaves. Infected plants demonstrate growth reduced, smaller ears with loose, small and discolored kernels or stained. Depending on the cultivar, it may present tillering and drying precocious. Foliar symptoms appear when the plants and other symptoms after grain formation and filling (Balmer& Pereira, 1987; Fernandes & Oliveira 1997).

Corn plants infested with Thin rayado show symptoms of the disease between 7 days and 10 days after inoculation, in the form of small aligned chlorotic dots. With the growth These points merge and form a thin stripe. In susceptible cultivars, the Early infection can lead to reduced growth and bud abortion florals.

The intensity of damage to the corn crop depends on the phenological phase in which the culture is attacked by the infected leafhopper. When the attack occurs in the phase initial stage of culture (V1 – V3-4), the greater the losses and the more later the infected leafhoppers reach the crop, the damage is less and losses.

D.maidis eggs - endophid posture (left) and D. maidis nymph (right).
D.maidis eggs - endophid posture (left) and D. maidis nymph (right).

Corn leafhopper management

Management strategies from the leafhopper D. maidis must be beginning before corn sowing, by eliminating tigueras plants during the off-season and during soybean cultivation, with the aim of eliminating the possible sources of food and reproduction of the pest, to reduce the pest population in the initial phase of development of corn sown in sequence. Such measures, in addition to possible reductions in the first generations of leafhoppers, also aim to reduce infected corn plants during these periods, which serve as a source of acquisition and subsequent inoculation of these pathogens in crops. However, as it is an insect with high biotic potential and with great capacity for migration over long distances to colonize newly emerged corn fields, these strategies must be carried out together with all producers in the same region.

The use of tolerant materials, or less susceptible is the most common control method. efficient and recommended for the control of these diseases transmitted by leafhopper D. maidis,. However, not all corn materials available on the market have satisfactory tolerance, Thus, it is up to the producer to make the best choice when purchasing seeds and opt for materials that present greater tolerance, with the aim of reduce losses.

Molicutes, responsible for infections of the phloem tissues in the corn plant, causing blockage of the vessels.
Molicutes, responsible for infections of the phloem tissues in the corn plant, causing blockage of the vessels.

As the most severe damage or transmission of phytopathogens occur in the initial phase of corn crop development, control measures in the initial phase are extremely necessary as they protect seedlings during this period, in addition to promoting or reducing the initial population, avoiding a population explosion of the leafhopper D. maidis in subsequent stages. Among the chemical control strategies adopted in the initial phase, Seed Treatment with insecticides neonicotinoids, is essential to reduce the pest population during this period culture development and has provided very effective results in controlling of this plague. In work carried out by Rattes Consultoria e Pesquisa Agronomia in partnership with the University of Rio Verde (UniRV), in the current harvest, the insecticides available on the market for seed treatment carried out with the molecules Thiamethoxan, Imidacloprid, and Clotianidin provided suppression of up to 80% of the D. maidis, up to 15 days after emergence of culture.

After this period, depending on the pressure and region, foliar applications are necessary of insecticides. Foliar applications must be carried out based on sampling of pest populations, with the aim of complementing the treatment of seeds and to control populations depending on production of new generations within the same crop or of insects migrating from areas neighbors. To date, there is no Economic Damage Level (NDE) that can be adopted due to being an insect that transmits phytopathogens. Thus, the Damages are not proportional to the size of the population, but rather a function of capacity to disseminate the causative agents of stunting, which makes the use of preventive measures is necessary. Foliar sprays are normally carried out up to the V8 –V9 stages in corn crops, and can be extend until the tasseling phase.

Among the possible management strategies of this pest, the producer must be aware that with the adoption of a single, in isolation, it will not be successful in controlling the D. Maides.

Article published in issue 217 of Cultivar Grandes Culturas, June 2017. 

Mosaic Biosciences March 2024