'A Nymph Is A Hidden Danger That Puts The Management Of The Corn Leafhopper At Risk', Says A Bayer Expert

Incorrect use of pesticides and difficulty in monitoring collaborate with pest population explosions. Understand how to solve!

São Paulo /PRNewswire/ - Integrated Pest Management is the main tool to combat the corn leafhopper, the insect vector of the Stunting Complex, which can reduce grain production in plants by more than 70%. susceptible, according to Embrapa. Among the actions are the elimination of tiguera corn, seed treatment and the application of pesticides. However, the habits of leafhopper nymphs make chemical control difficult and favor the explosion of infestation in crops.

The leafhopper has the capacity to deposit approximately 14 eggs per day, being able to lay more than 600 eggs during its 45 days of life. In addition to this large amount, the pest has a specific technique to protect the eggs throughout the cycle.

"The leafhopper has the ability to detach the adaxial epidermis of the leaf (film or cuticle) and deposit the eggs directly in the parenchyma cell tissue, generally close to the midrib, covering the eggs again with this film. In this way, it even protects the eggs of the pesticides that will be applied. This is known as endophytic oviposition", comments Bayer corn specialist Paulo Garollo.

Still demonstrating great survival skills, after the eggs hatch, the nymphs only move to the underside of the leaf and, from then on, remain practically immobile, feeding until they reach the adult stage. "The nymphal period lasts an average of 15 to 18 days and, due to the abaxial position of the nymph and the very low mobility on the leaf, products with contact action will hardly reach them and, consequently, they will have an extremely favorable survival environment", says Garollo.

In all, the nymphs go through five instars (stages of shedding their skin) until they become adults able to fly and look for areas with newer corns to restart the infestation. "It is for this reason that, even taking all the precautions and everything seems to be under control, from one day to the next there is an explosion in the infestation of insects in the areas. for the leafhopper to migrate from the oldest corn to the youngest", comments Garollo.

To make matters worse, the Brazilian climate is perfect for leafhopper infestation. Within an average temperature between 27°C and 30°C, practically 100% of the eggs of the pest hatch, in addition to being the ideal temperature for the development and shedding of the skin of the leafhopper nymphs.

"The nymphs are more easily infected with the causative agents of the Stunting Complex than the adult insects. In other words, they are a more powerful vector of the disease", guarantees the specialist from Bayer. "And, different from what one might think, they are not born with these causal agents, even coming from the crossing of infected parents, but they are easily contaminated when they are born in a diseased plant", he comments.

How to control?
Management only with contact pesticides can be useful against adult leafhoppers, but it has little efficiency in relation to nymphs, which remain immobile and protected under the leaf.

"The ideal in these cases is to choose a pesticide with high efficiency in translaminar translocation, which is the ability of a chemical product to cross the epidermis (film) of the leaf, in the upper part, and manage to pass through the parenchymal intercellular spaces", he says.

However, according to Garollo, the ideal is for the producer to create a chemical control strategy, to solve the problems and avoid unnecessary expenses.

"Before reaching the phenological period of four leaves, the farmer can and should, preferably, use contact products. This is because adult insects will arrive there and contact products will be ideal for this initial control. After this period, it is when the nymphs hatch from the eggs and then the producer must opt ​​for neonicotinoids with translaminar translocation."

It is necessary to pay attention to the indication on the leaflet, as contact pesticides, in general, should only be applied twice per crop cycle, while neonicotinoids that kill nymphs can only be applied three times per crop.

"Management of leafhopper nymphs is perhaps one of the main bottlenecks for the success of eradicating this pest. Something that is little commented on and disseminated. product to use and when to use it", says Garollo. "Producers end up letting the nymphs prevail and, consequently, there are explosions of leafhoppers, which are more attracted to plants already infected with the stunting complex, generating a large increase in the population of the diseased pest", warns the Bayer specialist.

Bayer Solutions against Stunting Complex
According to the Bayer specialist, the ideal is for the producer to start handling against leafhoppers by treating corn seeds with Cropstar®, a systemic insecticide from the chemical group of neonicotinoids (Imidacloprid) and thiodicarb, from the chemical group Methylcarbamate , bringing a broad spectrum of control and initial protection to crops.

Then, after the corn emerges and opens the first two leaves, it is time to apply Curbix®, an essentially contact product, from the chemical group of phenylpyrazole (Etiprole), which will be used to combat bedbugs and leafhopper adults. It must also have a second application, with an interval of at least seven days from the first application, after the two initial leaves are expanded (stage V2).

When the corn reaches the V4 stage, the producer can start applying Connect®, a systemic insecticide from the chemical group of neonicotinoids, associated with beta-cyfulthrin, belonging to the chemical group of Pyrethroids (contact), with the main function of translaminar translocation , which affects nymphs. But this product also helps to control adult insects, if they come into direct contact or by ingestion. Connect® will still help the producer in a second application, with an interval of at least seven days, in the V6 stadium. And it will also re-enter the V8 stadium, completing three applications with the product.

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