EN 
PT_BR 
According to the Argentine government, the diseases of corn These crops are undergoing changes in epidemiological behavior, distribution, and intensity in different producing regions. This scenario was analyzed by plant pathologist Enrique Alberione, from EEA INTA Marcos Juárez, during a Technical Update Day on Coarse Grain Crops, focusing on sanitary risks and strategies to reduce productivity losses.
Common rust, white spot, and smuts are among the main challenges faced by the crop. According to data released by INTA Marcos Juárez and the southern region of Santa Fe of CREA, results from regional research and trials can help in planning the next harvest.
The event was organized by INTA Marcos Juárez and the southern region of Santa Fe of CREA, as part of a collaborative effort to generate and validate information aimed at decision-making. The program brought together research results and tests conducted by technicians from both institutions.
In the case of common rust, the impact on productivity depends on environmental conditions and the susceptibility of the hybrid. Losses can range from 5% to 10%, reach 15% to 30% in susceptible hybrids, and reach 40% to 60% in severe infestations. In Argentina, reductions of 3% to 8% in grain weight were also recorded when disease severity reached 10%.
The fungus that causes common rust, *Puccinia sorghi*, has a life cycle that depends on an alternative host of the genus *Oxalis*. According to Alberione, this characteristic means that the pathogen needs two plant species to complete its development and survive between harvests. "It is classified as a heteroecious pathogen, since it absolutely needs two different plant species to complete its entire life cycle," he noted. Infection is favored by temperatures between 16°C and 23°C, high relative humidity, the presence of dew, and at least eight hours of leaf moisture.
During the 2025/26 growing season, however, the disease's behavior differed from what was expected. Incidence and severity were low in early-planted corn, while rust was more prevalent in late-planted fields. "This would be inversely related to what we know about the disease, because rust should decrease at higher temperatures. However, it was more prevalent in late-planted corn, so we may be facing a possible change in the pathogen's behavior," warned Alberione.
Given this scenario, genetic resistance remains one of the main tools for management. Hybrids can combine qualitative resistance, which restricts sporulation, quantitative resistance, which reduces severity, dissemination and spore production, and adult plant resistance, which combines both mechanisms and is mainly expressed in the reproductive stages.
Trials conducted by CREA Sur in Santa Fe, in Teodelina, Benjamín Gould and Las Rosas, showed strong variability among the hybrids evaluated.
About half of the materials showed acceptable genetic resistance. The remainder demonstrated greater susceptibility, although infection levels remained low.
Chemical control also reduced average severity. “Comparing the control treatments with chemical control, in Teodelina the severity ranged from 1.7% to 0.7%, in Benjamín Gould from 0.7% to 0.1%, and in Las Rosas from 1.7% to 0.6%. This confirms the importance of complementing genetic resistance with fungicides to mitigate health risks,” explained Alberione.
White spot disease also requires attention. Considered an emerging disease in Argentina, it was first reported in the 2010/11 crop season in the Rafaela region of Santa Fe.
The importance of the disease has already been recorded in other countries. In China, productivity losses range from 10% to 50%, while in Brazil they can reach 80% in severe outbreaks.
Furthermore, studies indicate that for every 1% increase in severity, productivity decreases by 0.23% and grain weight drops by 0.16%. According to Alberione, white spot is caused by a complex formed by the bacterium Pantoea ananatis and the fungi Phaeosphaeria maydis and Phyllosticta spp. The bacterium initiates the infection, and subsequently, the fungi can develop in the lesions.
The pathogen can survive in crop residues, seeds, and host weeds, such as Digitaria horizontalis, which favors its persistence between harvests. Temperatures between 20°C and 23°C, prolonged periods of leaf moisture, and mechanical damage caused by hail, wind, or rain are among the conditions that favor the disease.
The potential advance of an El Niño scenario is also a concern. "So far, we've been observing it mainly in late-planted corn, but if the conditions of lower humidity and temperatures extend to early plantings, the disease could start much earlier. We must remain vigilant," warned the plant pathologist.
Trials conducted by CREA Sur in Santa Fe identified a prevalence of 100% disease in the 11 hybrids evaluated in Teodelina and Las Rosas. The intensity, however, differed between the environments.
In Las Rosas, the average incidence reached 98% and the severity 30%. In Teodelina, the incidence was close to 24% and the severity was only 0.7%.
In the INTA Marcos Juárez trial network, the disease was present in 63% of the evaluated environments. The prevalence at the hybrid level reached 100% in Sol de Mayo and Morrison, 70% in La Norte, 20% in Coronel Moldes, and 5% in Adelia María.
An AAPRESID trial in an early planting area near Marcos Juárez also detected white spot, although only in one hybrid. The result suggests that the disease may begin to advance into earlier planting dates.
For management, Alberione highlighted the combination of planting time, crop rotation, density adjustment, and sanitary characterization of the hybrids.
The plant pathologist also warned that high doses of nitrogen can promote the development of diseases. Chemical control, in turn, has limitations because fungicides act on fungi, but not on the bacteria that initiate the infection.
Among the alternatives evaluated in the literature are treatments with mancozeb, a multi-site fungicide, as well as azoxystrobin and difenoconazole. However, efficacy depends on the timing of application and the predominant causal agent.
Corn smuts are also on the sanitary radar. Alberione differentiated the epidemiological behavior of common smut, caused by Ustilago maydis, and ear smut, caused by Sporisorium reilianum. Both diseases originate from teliospores, but they differ in the form of infection and the damage caused to the plants.
Common smut causes localized infections in young tissues and is favored by injuries caused by hail, wind, or insects. Ear smut, on the other hand, initiates infection during emergence, when the fungus penetrates through the roots or coleoptile and colonizes the entire plant.
Therefore, ear smut exhibits systemic behavior. Plants may become stunted, have short internodes, multiple ears, and deformed panicles, which are eventually replaced by charcoal-like masses.
Environmental conditions also differ. Common coal thrives in temperatures between 26°C and 34°C, water stress, high nitrogen levels, and the presence of wounds.
Ear smut, in turn, is favored by soil temperatures between 21°C and 28°C during planting and does not depend on the occurrence of lesions to infect the plant.
While common charcoal typically causes yield losses of 5% to 30%, ear charcoal can prevent grain formation and lead to losses of up to 80%.
Surveys conducted by INTA in eight late-planting areas detected common smut with prevalence rates of up to 40%. The results showed significant differences between locations and hybrids.
Some varieties showed an incidence close to 5%, while others did not present affected plants, demonstrating different levels of genetic resistance. "It is important to characterize the varieties regarding resistance to all diseases, and this one in particular is no exception," noted Alberione.
Corn smut is considered a re-emerging disease. According to data released by INTA, surveys conducted in 2023/24 identified its distribution in Córdoba, southeastern Santa Fe, San Luis, and Buenos Aires.
In plots near Chañar Ladeado and Corral de Bustos, productivity losses close to 50% were estimated in different years.
In the current growing season, a trial conducted near Corral de Bustos evaluated the performance of commercial hybrids against ear smut. The results were more positive.
Of the 25 hybrids evaluated, 72% showed incidence rates between 0.% and 1.3%, confirming the existence of materials with a good level of genetic resistance.
Results obtained by teams from the Catholic University of Córdoba, INTA, and private companies, in the Corral de Bustos and Camilo Aldao environments during the 2023/24 campaign, also showed variability in the genetic behavior of the materials.
In the first environment, disease records ranged from moderate to severe, while in the second they were considered mild. Even so, a large portion of the materials showed minimal presence of the disease.
In this context, Alberione highlighted the importance of sanitary characterization of hybrids to identify materials with greater genetic resistance. In the trials evaluated, most showed an incidence lower than 2%, reinforcing the potential of the tool for managing corn diseases.
