Soybean cultivation can mitigate target spot in cotton farming

Cotton production in Brazil continues to grow, placing the country in third place among the world's largest producers, according to the Brazilian Cotton Producers Association (Abrapa). However, challenges for producers continue with the increasing incidence of diseases such as target spot, which in severe conditions can cause productivity losses of up to 40%, according to studies by Embrapa. 

Diego Palharini, technical consultant at Tropical Melhoramento & Genética (TMG), a company that develops genetic solutions for cotton, soybeans and corn, explains that target spot has a direct impact on cotton yield, as it mainly affects the leaves, causing early defoliation and, consequently, a reduction in the plant's photosynthesis capacity. "This interferes with the production of photoassimilates and results in the formation of smaller, lower-quality bolls, in addition to compromising the final weight of the fiber," he explains.

Another aggravating factor for the occurrence of the disease is the survival of the fungus in crop residues, which increases its presence in the field, especially in areas where there is no adequate crop rotation. "It is a disease that survives in crop residues and, with the increase in productivity and intensification of crops, chemical control of target spot has become less efficient over the years," comments Palharini.

In addition to crop residues, climate conditions also impact the development of target spot. The fungus thrives best in warm, humid environments, which is common in Brazil's cotton-producing regions, especially during rainy periods. "Temperatures between 20°C and 30°C, combined with high relative humidity and prolonged periods of leaf wetness, create the ideal scenario for the spread of the disease," explains the specialist, who adds that "these factors contribute to the rapid spread of the fungus in the field, affecting plants more intensely, especially in the summer months, when cotton and soybeans are in important stages of development," he says.

Integrated management begins with the choice of cultivar (regardless of the crop) 

The consultant explains that integrated management of target spot involves multiple techniques, such as crop rotation with non-host species to reduce fungal inoculum in the environment, proper management of crop residues, and use of seed treatment with fungicides to delay initial infection. These practices are important considering that, currently, there are no cotton and soybean cultivars with total genetic resistance to target spot. However, there are differences between cultivars, and because some cultivars are less susceptible to the disease, some are classified as having moderate resistance to target spot.

In view of this, producers need to adopt alternative strategies to mitigate the occurrence of the disease. Although rotation between soybeans and cotton is excellent for some agronomic aspects and economic viability, in the case of target spot, since both crops are hosts of the pathogen, the disease ends up favoring each other. However, there are alternatives to minimize the damage. The consultant emphasizes that choosing soybean cultivars with moderate resistance to target spot is a good alternative.

"By planting moderately resistant soybeans in the same area where cotton will be grown in the following harvest, the presence of inoculum in the soil is reduced, reducing the pressure of the disease on the cotton plant and mitigating the damage caused by the disease, especially at the beginning of the cycle," explains Palharini. He emphasizes that this practice does not completely eliminate the disease, but it reduces its incidence, giving the producer more time to adopt control measures and minimize the impact on the final yield.

Another way to enhance management, according to the consultant, is to use cotton cultivars that are tolerant to other diseases. According to him, “when we use cotton cultivars that are tolerant to ramularia (the main cotton disease), for example, we can intensify the use of specific fungicides for the target spot, since ramularia can be controlled more easily. This allows for more targeted and efficient management of the target spot disease, in addition to helping maintain the effectiveness of specific fungicides.

TMG is constantly investing and working to develop and select soybean and cotton cultivars that increasingly show good performance for the target spot. The use of these cultivars and integrated management that includes several management techniques will continue to be the best strategy to mitigate losses", concludes Palharini.