By Nico van Burick
Several farmers in the western parts of the summer rainfall region are currently experiencing problems with their crops due to head and stem rot caused by the fungal disease Sclerotinia, resulting from late plantings and unfavourable weather conditions.
Regarding sunflowers, some farmers are experiencing low to very low yields, and the National Crop Estimates Committee (CEC) has adjusted its estimate downward, according to Grain SA’s latest report on the delivery of grain and oilseeds. According to the CEC’s production forecast for 2025–26, about 727 800 tonnes of sunflower seed can be produced this year. The production estimate has been reduced by approximately 15 000 tonnes, but it remains 95 800 tonnes more than the total production of the previous season.
Dr Lisa Rothmann, a senior researcher in plant pathology at the University of the Free State and chairperson of the research network for Sclerotinia, notes that trials are underway for sunflower at Groblersdal in Limpopo and Delmas in Mpumalanga. When they drove there from Bloemfontein recently, she says they saw farmers harvesting sunflowers and observed places where damage from Sclerotinia was visible.
“It can limit yields due to head rot. In the case of soybeans with stem rot, the damage can be less, depending on the severity of the infection.”
“Many farmers only plant sunflowers after they have planted maize and soybeans, and these later plantings worsen the risk of the disease in sunflowers. What further worsens the risk with sunflowers is that there are currently no chemical products registered to combat head rot. Our research group continues to conduct registration trials in collaboration with companies. For soybeans, some products can combat the disease.”
She says significant head rot due to the fungal disease has been reported in the Free State and North West.
The planting date and the type of cultivars planted play a role in Sclerotinia infection. “The earlier planting is done and with cultivars that have a short growing period – specifically with soybeans – Sclerotinia can be avoided. The flowering period determines the risk of infection.”
Dirk Laas, who farms at Ottosdal, says he has not experienced problems with Sclerotinia because he planted sunflowers early, but in his area, some farmers are struggling with the disease.
“I did struggle to harvest because, at the end of March, it was still very wet. I know some farmers are now struggling due to the fungal disease, but fortunately, the weather is no longer as wet. Here and there, farmers are starting to harvest maize.
“The fact that it was so wet late in the season caused the impact of fungi to be worse than in the past. Sunflower fits well into our planting cycle, and we will have to find a solution against Sclerotinia.”
Jozeph du Plessis, a farmer from Schweizer-Reneke, says that although they experienced record-high rainfall during the season, they experienced very little Sclerotinia in soybeans. However, currently, there is a severe outbreak of Sclerotinia in sunflowers due to late plantings.
Rothmann says that regarding soybeans, a few farmers who have never dealt with it before have contacted her. This could be new areas with outbreaks or cases where farmers had not previously noticed the fungus. She says that at Schweizer-Reneke, several instances of stem rot in soybeans have been reported, but at Lichtenburg, only one case has been reported.
“It is important because it shows that in some years, many cases occur in a specific area, but in other years, there are none. This could be due to the sporadic occurrence of the disease, but it could also be that farmers do not report it, do not notice it, or do not know where and how to report it.”
She says farmers can contact her via WhatsApp at 079 270 9691 to report Sclerotinia or to make inquiries about the symptoms.
Sclerotinia also occurs in various other crops. It has been reported in dry beans in the Northwest and groundnuts at Bloemhof, Bultfontein, Bothaville, Hoopstad and Odendaalsrus. Rothmann notes that there were even cases of the disease in cabbage (2023), lettuce (2022), and vegetables such as pumpkin and green beans.
She warns that as the canola season progresses, farmers should be on the lookout for signs of the fungus on this crop as well.
Also read:
Severe weather causes Sclerotinia to flare up again
