Effective control of Helicoverpa and false caterpillars

Helicoverpa armigera e Chrysodeixis includens there are two pests with high potential to cause damage to various crops such as soybeans, corn, beans and cotton. By the way it lodged in plants, they become targets difficult to reach by the application of insecticides. Therefore, in addition to correct choice of product, proper use of application technology is essential for the success in controlling these insects.

Agricultural production requires constant efforts, dedication, knowledge and discernment. Great challenges present themselves day after day producer, who to face them uses the most advanced technologies, modern, high-performance machinery, certified seeds, fertilizers, adapted management models and highly profitable cultivation systems. At the pest control, however, despite offering all these tools, there is no It is rare for a spray to fail because the target is not reached. Sometimes There are pests that are difficult to control, either due to their tolerance or resistance to certain molecules, due to their location and positions in the plant where it is not easy for drops to reach, or even due to an inadequate dose of the insecticide product. In between These pests are polyphagous species, such as Helicoverpa armigera e Chrysodeixis includens, whose population control is not always achieved by spraying, inducing increasing intensification of the use and doses of chemical insecticides, resulting in increased production costs and direct damage to production. The misuse of application technology has been constantly cited among the likely causes of failure in controlling these insects, demanding further research specific for the application of chemical and biological insecticides used in control of these lepidopterans.

Crops such as soybeans, corn, beans and cotton are attacked by the two pests that move between crops at different times, which favors their survival and the increase in populations. In recent harvests Helicoverpa caterpillars (Helicoverpa armigera) and false-measurement (Chrysodeixis includens) have become more frequent, causing significant damage and demanding control actions from farmers. The extent and proximity of bean, sunflower and soybean crops, mainly, determine the permanence and consequent migration of moths to cotton crops. It is host succession allows these pests to remain at high density in the agroecosystem, another reason for its frequent outbreaks.

Plague known in others grain and fiber producing regions of the world, Helicoverpa armigera its occurrence was recorded for the first time time in Brazil in the 2012/2013 harvest in areas of the cerrado, associated with soy and cotton. Since then, population outbreaks have become frequent, including in some transgenic crops. These caterpillars feed on leaves and stems, but has a preference for reproductive structures. The adults are strongly attracted to the nectar of flowers, which influences the choice of host plants is significant. Furthermore, H. armigera has great capacity for adaptation to adverse environmental conditions of extreme temperatures and low relative humidity. But, obviously, if the climate is favorable, greater will be the ability to maintain high populations, a common fact in some states Brazilians, such as Bahia, which has a hot and dry climate combined with diverse of host cultivated plants, where the occurrence of this pest and its damage are bigger. Currently distributed throughout grain and fiber producing regions of Brazil, from South to Northeast, is found feeding on plants dicotyledons such as beans, soybeans, also in crops such as cotton and smaller extent in millet, sorghum and corn crops. Furthermore, what worsens the situation is the fact that this species has presented lineages that have tolerance or even resistance to insecticides and genetically modified. It is estimated that the worldwide loss caused by this pest reaches five billion dollars. In Brazil, the estimated losses are in the order of two billion reais until the 2012/2013 harvest. 

Chrysodeixis includens have their young form popularly known as false-measure, and both small as well as large caterpillars are found feeding on the lower third of plants and tender leaves of secondary branches of soybeans, sunflowers, beans and cotton. But it is constant to note that during the first and second instars the caterpillars they only scrape the leaves, while, from the third instar, they can drill them, leaving, however, the central and lateral ribs intact, providing a characteristic appearance of lacy leaves, reducing photosynthetic capacity of the plant. Its polyphagy allows it to develop into 73 species of host plants in Brazil. False meter outbreaks appear to be greater in agroecosystems where soybeans and cotton are grown Upcoming. Some studies have found an increase in longevity, oviposition and frequency of copulations, when nectar from cotton flowers was provided for adults from C. includens. This in part may explain the higher population rate of C. includens in soybeans, when there is cotton area in the nearby. This condition commonly occurs in Central Brazil, in areas agricultural areas where there is a succession of these crops and constant overlapping of areas of cultivation involving soybean and cotton crops.

The main method of controlling these pests has been the chemical, often carried out improperly, without a correct sampling that would indicate the ideal moment of application. Authors mention that the appropriate time for chemical control of these species would be in the first larval instars, as the caterpillars feed preferentially of the most tender parts of the plants and, therefore, would be more exposed and susceptible to contact with the applied products. However, not always the spraying is done under this ideal situation, more information is needed regarding the behavior of these pests, which are difficult to control chemical. The difficulty of reaching the target becomes greater in situations where that these pests preferentially occupy the interior regions of crops (middle and lower portions of plants), requiring greater droplet penetration so that the products can act on the target pest. Because of this, it is common consider the application technique used and/or associated operational condition as one of the causes of failure in control.

For the adequacy of insecticide recommendations with satisfactory control efficiency, in the 2016/2017 harvest, bioassays with Helicoverpa armigera e Chrysodeixis includens, Besides evaluations of four different insecticides with action modes in caterpillars third instar, middle stage of the development cycle.

Efficiency of control of Helicoverpa armigera bigger that 75% was verified with the use of the entire dose (recommended dose in the leaflet) and double the dose of Baculovirus (HzSNPV) and all doses of flubendiamide (Figure 1). The other products resulted in control efficiency below 75%. Against Chrysodeixis includens, efficiency of control equal to or above 75% was verified with the use of lufenuron and flubendiamide. Other products resulted in a maximum control efficiency of 53%. In tests with both species of caterpillars, the efficiency of the products and their respective doses in the pupal was always relatively low, reaching a maximum of 5%, which demonstrates that the lethal action of the products was concentrated in the larval phase.

The cumulative daily larval mortality of H. armigera promoted by B. thuringiensis varied over time, but little exceeded the value of 50%, regardless of the dose used (Figure 2a). Increment trend of mortality with increasing dose was observed with Baculovirus (HzSNPV), and the recommended dose promoted final larval mortality close to 80% and the use of twice the dose increased mortality to values ​​close to 100%. Lufenuron promoted increasing larval mortality in the first five days, stabilizing after this period at levels between 50% and 60% when used half dose and full dose, and close to 80% when twice the dose is used. As for flubendiamide, larval mortality was significantly increased in the first five days after exposure, stabilizing at high values ​​between 90% and 100%, even when half a dose was adopted (Figure 1d).

The cumulative daily larval mortality of W. includens promoted by B. thuringiensis applied in half dose and recommended dose did not reach 40%. When twice the recommended dose was used, mortality reached a slightly above 60% at the end of the larval stage. Baculovirus (ChinSNPV) promoted increasing mortality throughout the larval stage, but accumulated larval mortality ranged between 50% and 65%, this maximum value resulting from the use of twice the recommended dose. Mortality due to the use of lufenuron occurred in first seven days of the larval phase and reached values ​​close to 100%. The same pattern of mortality was verified with flubendiamide, and the values resulting final values ​​varied between 80% and 100%, proportional to the dose used.

You results allowed us to conclude that among the products tested, the most efficient for controlling Helicoverpa armigera were flubendiamide at a dose of 75 ml p.c./ha, baculovirus (HzSNPV) at a dose of 1500 g p.c./ha and lufenuron at a dose of 2000 ml p.c./ha. Against Chrysodeixis includens, lufenuron in dose of 500 ml p.c./ha and flubendiamide at a dose of 75 ml p.c./ha were the most efficient.

Important It should be noted that for both species only half the dose was required recommended dose of flubendiamide to obtain the desired control. Of the same way, for the control of C. includens, lufenuron was efficient even with half a dose (500 ml p.c./ha). In practice, however, it is common sense to maintain the recommended dose, as the tests were carried out in a laboratory environment, without the presence of other factors adverse to spraying, while in the field the action of the products can be affected by biotic and abiotic factors.

Products and appropriate doses to control crop pests are part of the technology of application. The interaction of factors related to the product and those related to culture, the environment and the characteristics and conditions of the applicator equipment contribute to efficient control, cost reduction and of environmental impacts. Therefore, in addition to the product and appropriate dose, one must pay attention to good adjustment of the sprayer and the correct moment of application, considering the susceptible phase of the pest, the time of application, the conditions temperature, humidity and wind. The weather conditions must be favorable to absorption and translocation of products, indicating temperatures between 20ºV and 30ºC, relative humidity between 60% and 70% and wind speeds below 10 km/h. It is not prudent to carry out applications in case of imminent rain, as it may there is loss of product due to runoff. The volume of solution to be applied, the number and size of drops, operating pressure of the nozzles, agitation and addition of adjuvants must be checked carefully. Finally, It is recommended that the producer always consult an agronomist to assist him in measuring all these factors.

Article published in issue 225 of Cultivar Grandes Culturas, February, 2018.