The sugarcane borer (Diatraea saccharalis) is one of the main pests of sorghum, depending on the population density of this insect in the field. This is the conclusion of the first study that determined the level of economic damage in grain sorghum and that effectively shows how much yield is compromised due to borer infestation.
In general, the results of this study, which used commercial hybrids commonly planted in Brazil, showed susceptibility of grain sorghum to the sugarcane borer, also known as the stalk borer, under high levels of infestation, causing substantial losses in productivity when not treated with the insecticide.
The article "What is the potential of sugarcane borer in reducing sorghum fitness and grain production?", published in the Journal of Applied Entomology, records a study carried out during three harvests, between 2021 and 2023, at Embrapa Milho e Sorgo, in Sete Lagoas (MG). The study is part of the doctoral thesis of Camila da Silva Fernandes Souza from the Federal University of Larvas (UFLA), supervised by Professor Bruno Henrique Sardinha de Souza, and by Simone Martins Mendes, a researcher at Embrapa.
“Recently we have been talking a lot about the sorghum aphid (Melanaphis sorghi), obviously, because it has caused great damage to crops of this cereal due to the difficulty of controlling it. However, this study shows the damage caused by the stem borer in the crop”, reports the Embrapa scientist.
She says that the borer often goes unnoticed because of its habit. It lives hidden inside the stalk of the sorghum plant, whose losses were measured for the first time in this study and, depending on the hybrid, can reach around 50% of the production.
Many of these losses have been controlled with the use of insecticides, both for fall armyworm (Spodoptera frugiperda) when for the sorghum aphid (Melanaphis sorghi). “However, it is essential to be aware of the borer in sorghum crops, as the injuries often go unnoticed by the producer”, reveals Mendes.
The researcher reports that, recently, the sorghum aphid has been receiving a lot of attention from producers. It is a pest that has only recently been detected in the crop. The first reports of economic losses were made in the 2018/2019 harvest. “In addition to the severe losses it has been causing, however, we cannot be negligent in monitoring other crop pests, such as the borer,” warns Mendes.
The sorghum borer was capable of causing yield losses of up to 100% in more severe cases, when the plants were not treated with insecticide in a less tolerant hybrid. The most productive and tolerant hybrid recorded a loss of 50%. This shows how sorghum hybrids can behave differently in the field under the same pest infestation. Therefore, it is also important for the producer to be aware of the infestation of this pest in the field, since the use of a susceptible hybrid combined with the non-use of insecticides can lead to severe losses.
“Despite the importance of this insect pest species, little was known about the relationship between borer infestation and reduced sorghum grain productivity. Another demand was to know the profit threshold and the level of economic injury for making pest control decisions,” commented Camila Souza.
“As published in the study, we carefully measured both the parameters of this pest’s infestation and crop productivity. We assessed the length of the galleries caused by the borer’s feeding, as well as plant height, length and weight of panicles, as well as stem borer injury and compromised grain productivity. Sugarcane borer infestation was greater when the sorghum plants were not treated with insecticide, resulting in lower productivity,” explains Souza.
With the use of insecticide to control the pest, an increase in plant height was observed, mainly due to the reduction of galleries (holes) caused by the borer in the plant stems, which prevents the translocation of photoassimilates through the plant and, consequently, increases the length and weight of the panicles.
Two commercial hybrids showed a reduction in grain production with increasing gallery length, while sorghum BRS 373 did not show a significant correlation, which may suggest a certain level of tolerance to sugarcane borer attack.
The study was a pioneer in determining the profit threshold and the level of economic damage caused by the attack of this caterpillar in grain sorghum hybrids. This information is essential for farmers because it allows them to better plan their crops, knowing that it is necessary to take control measures if the pest infestation reaches 3% intensity”, points out Camila Souza.
The level of economic damage is the lowest density of insects, or their damage, that causes economic loss. “When the cost of pest control is equal to the loss of productivity caused by the population density of the sugarcane borer. Market values may change over time according to current economic conditions,” says Souza.
The calculations were based on average data from the last five years. For the value of a 60 kg bag of sorghum grains, in dollars the value considered was US$ 8,62. The average cost of application via soil per hectare for controlling the Sugarcane Borer was US$ 25,9, taking into account the price of the commercial insecticide per hectare applied. Quotations were made from the main resellers for one application, according to the Physical Market-Sorghum, 2022.
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