Proper management can prevent sorghum blight

This harvest, many sorghum farmers faced problems with the disease known as ergot, mela or sugar disease. This disease, which occurs a lot in colder conditions, has established control measures, as researchers recommend. 

“Several reports of the occurrence of mela have been made by farmers who are starting to grow sorghum in areas where little is known about the crop. In many of them, sorghum has become an option to off-season corn, due to high losses due to stunting”, says researcher Dagma Dionísia da Silva, from Embrapa Milho e Sorgo.

Despite its potential for losses, this disease can be avoided by farmers with the use of appropriate management practices before sowing and during the sorghum flowering phase. “Using cultivars adapted to the region and sowing at the most appropriate time are practices that help prevent sorghum sugar disease. This is because the severity of the disease is favored by minimum temperatures of ± 13 °C to 19 °C and relative humidity of 76% to 84% and by unfavorable conditions for the supply of pollen”, explains the researcher.

“It is recommended to remove remaining sorghum plants and secondary host plants of the pathogen (Table 1). Furthermore, the proportion of male-sterile and restorative lines must be adjusted in seed production fields to ensure good pollen availability, since infection does not occur in fertilized flowers. And for quick fertilization, the farmer must plan the planting so that there is a good coincidence of flowering between the male and female lines.”

Another detail to be observed is whether the seeds form fungal survival structures, called sclerotia. “In this case, you can soak the seeds in a 5% sodium chloride solution, so that the residues float and are eliminated from the batch”, teaches Silva.

To apply fungicides, products registered with Agrofit/Mapa must be chosen. “Applications must begin when the flag sheet is issued and continue every five days until flowering is complete. Currently, twenty commercial products are available on Mapa for honeydew control (Table 2). It is worth mentioning that it is always important to rotate between active ingredients/chemical groups to avoid selection pressure on the fungus and loss of these active ingredients”, he points out.

The researcher also clarifies that “there are no risks, despite there being great concern among producers about the possibility of toxicity of sorghum honey for consumption of grains or silage, by humans and animals, unlike what happens with other species of this type. genus of fungi”.

How to recognize mela

Sorghum is a crop that adapts to different soil and climate conditions in Brazil, but can be affected by several diseases. In Brazil, mela was observed for the first time in 1995, throughout the Center-South region of the country, with widespread occurrence in Minas Gerais, São Paulo, Goiás and Santa Catarina.

“The disease, also called ergot or sugar disease, is caused by the fungus Sphacelia sorghi. It is recognized on the plant by the presence of thick, pink to brown, sugary drops that emerge from the inflorescences. These sugary drops contain the fungus' conidia, which are dispersed by insects, attracted by the sugars. Wind and water splashes are also forms of dispersion. In more advanced stages, there may be the formation of whitish sclerotia (fungal survival structures) that contaminate seed lots”, explains researcher Dagma Silva.

“Mela causes quantitative and qualitative losses in sorghum, especially in the production of hybrid seeds, when male-sterile lines are used, which are highly susceptible to the fungus S. sorghi. The fungus colonizes the unfertilized ovary and for this reason, in infected flowers, grain production does not occur. In this way, large losses occur.”, he highlights.

“Qualitative losses occur because the sugary drops attract opportunistic fungi. These fungi colonize the drops, giving them a dark appearance similar to charcoal. Furthermore, the sugar drops fall on the leaves and on the grains that may have been produced, making harvesting difficult, as they stick together”, adds Silva.