Fungicide and Resistant Variety Combo Slashes Sunflower Powdery Mildew in Ethiopia

In the lowland and mid-altitude districts of South Omo Zone in southwestern Ethiopia, sunflower farmers have long watched a pale, dust-like disease creep across their fields and quietly strip away their harvest. A two-year field study conducted in the Debub Ari and Salamago districts now offers those farmers a concrete, economically tested defense. By combining an improved sunflower variety with carefully timed fungicide sprays, researchers cut powdery mildew severity by more than 90 percent in some plots and lifted yields by nearly half compared with untreated local practice.

The disease in question, powdery mildew, is caused by the fungus Erysiphe cichoracearum. It announces itself as minute discolored specks on sunflower leaves, from which a powdery white mass radiates outward until entire leaves are coated. Under the warm conditions typical of tropical regions, the infection can escalate to complete defoliation, and the resulting loss of photosynthetic surface translates directly into fewer and lighter seeds. While sunflower is among the world’s most cultivated oil crops, with global production around 40.21 million tons annually across roughly 26.05 million hectares, Ethiopia’s national average yield sits at only about 1.033 tons per hectare, dragged down in part by this and other fungal diseases.

The research team set out to test whether pairing host resistance with chemical control could suppress powdery mildew epidemics more effectively than either strategy alone. They evaluated two sunflower varieties, the improved Russian black and a local variety, in combination with three fungicides: propiconazole 25% EC, a systemic triazole; wettable sulphur 80%, a contact fungicide; and mancozeb 80%, another contact product. Each fungicide was applied either once or twice per season, producing fourteen treatment combinations that were arranged in a randomized complete block design with factorial structure and three replications under field conditions.

The choice of fungicides reflects three distinct modes of action. Propiconazole, as a triazole, moves systemically through the xylem of the plant and blocks the biosynthesis of ergosterol, an essential component of fungal cell membranes; without this sterol, the fungal cell wall is irreversibly damaged and the pathogen dies. Wettable sulphur interferes with cellular respiration in fungal pathogens, while mancozeb reacts with sulfhydryl groups in fungal proteins. Because these chemicals attack the fungus in different ways, the researchers reasoned that their performance under field conditions might differ substantially, and the data confirmed that prediction.

Disease assessments were rigorous. Ten plants per plot were randomly selected from central rows and marked for repeated observation, with incidence calculated as the percentage of plants showing symptoms and severity rated on a 1-to-9 scale that was converted to a percent severity index. From these repeated measurements, the team computed the area under the disease progress curve, or AUDPC, a single value that integrates initial disease intensity, the rate of epidemic development, and the duration of the epidemic, providing a compact signature of how aggressively the pathogen spread in each plot.

The results were striking. At Debub Ari, untreated local variety plots suffered a mean disease severity of 63.7 percent, while plots planted with Russian black and sprayed twice with propiconazole showed only 3.7 percent, a 94.2 percent relative reduction. At Salamago, the corresponding values were 39.25 percent for untreated local plots and 5.92 percent for the best treatment. Plots of the improved variety treated twice with wettable sulphur and plots receiving a single propiconazole spray also performed strongly, reducing severity by 86.3 percent and 81.6 percent respectively compared with the untreated local check. The AUDPC analysis mirrored these patterns: untreated local plots accumulated 778.74 percent-days of disease at Debub Ari and 489.93 percent-days at Salamago, whereas Russian black with two propiconazole applications kept the epidemic to just 102.84 percent-days at the first site, with wettable sulphur treatments close behind at the second.

Correlation analysis revealed how tightly the disease was linked to productivity. At Salamago, percent severity and AUDPC were almost perfectly correlated with each other, and grain yield showed strongly negative associations with both disease measures. Head diameter and thousand seed weight also declined as disease pressure rose. Similar negative relationships between disease parameters and yield emerged at Debub Ari, confirming that every increment of mildew severity translated into measurable losses in the components that determine final harvest weight.

Yield data told the same story from the opposite direction. The highest yields came from Russian black plots treated with propiconazole twice, reaching 2869.8 kilograms per hectare at Salamago, followed by 2841.3 kilograms per hectare with a single sulphur spray and 2834.9 kilograms per hectare with two sulphur applications. Closely similar trends appeared at Debub Ari. Untreated local variety plots, by contrast, yielded just 1289.5 kilograms per hectare at Debub Ari and 1574.6 kilograms per hectare at Salamago. Plant height and head diameter also responded to treatment, with the tallest plants and largest heads generally found in the improved variety under effective fungicide programs.

The economics proved equally persuasive. In a partial budget analysis that accounted for fungicide costs, local market prices, and a 10 percent downward adjustment of experimental yields to reflect realistic farm conditions, the highest net benefits came from Russian black sprayed once with propiconazole, followed by the two-spray propiconazole program and the sulphur treatments on the same variety. Untreated local plots delivered the lowest returns by a wide margin. Gap analysis summarized the practical advantage: treated plots reduced mean disease severity by roughly 91 percent compared with usual agro-pastoral practice and offered a 45.58 percent yield advantage over unsprayed controls.

The authors conclude that integrating the improved Russian black variety with propiconazole 25% EC at 0.1 percent concentration, followed by wettable sulphur 80% where appropriate, offers farming communities in South Omo a reliable and affordable strategy against powdery mildew. Because propiconazole is already available in local markets and provides both curative and protective action, adoption barriers are low. For a crop that anchors edible oil production across the region’s drought-prone landscapes, the study suggests that a modest investment in variety choice and spray timing can transform powdery mildew from a chronic yield thief into a manageable problem.

Subject of Research: Integrated management of sunflower powdery mildew using resistant varieties and fungicides in southern Ethiopia

Article Title: Management of sunflower powdery mildew through varieties and fungicides application in Debub Ari and Salamago districts of South Omo, Southern Ethiopia

Article References: Management of sunflower powdery mildew through varieties and fungicides application in Debub Ari and Salamago districts of South Omo, Southern Ethiopia. (n.d.). https://doi.org/10.3897/ia.2025.143321

Image Credits: AI Generated

DOI: 10.3897/ia.2025.143321

Keywords: sunflower, powdery mildew, Erysiphe cichoracearum, fungicides, propiconazole, wettable sulphur, Ethiopia, South Omo, plant pathology, crop yield, integrated disease management, agronomy