In 2014, 20% of the potato harvest on the farm Bottervlei in South Africa’s Western Cape Province was lost to rhizoctonia.
“We didn’t have a chemical product that could guarantee clean soil. We had already treated all of our seed potatoes with Mancozeb (Reg. no. L7381), a fungicide, but it was only effective during the beginning of the season.
“Rhizoctonia thrives in the top 5 cm of soil where there’s more heat, so, when the seed potato germinates, the rhizoctonia destroys the shoots before they emerge. Later in the season, the fungi also started to attack the tubers. We’ve even removed a potato that looked like a truffle because of all the rhizoctonia infection.
“In 2015 we decided to experiment with biological products for the first time. Initially, we still applied Mancozeb to the seed potatoes, and added Monceren (Reg no. L3123), a contact fungicide, to the furrows with the plants. Following this, between weeks 7 and 9 after emergence, we applied 500 ml/ha of BacToLife and 500 ml/ha ScleroStop from BacTech. Although this had an effect, it wasn’t as effective as we’d hoped and we lost about 10% of the harvest,” Farm Manager Maritz Hanekom explains.
The prescribed dosage for BacToLife and ScleroStop is between 1 l/ha and 1.5 l/ha, and in 2016 Hanekom, following the promising results achieved with the application of 500 ml/ha, decided to apply the full dosage.
Jaco Meyer from Metanoia Agri, distributors of BacTech’s products in the southern parts of SA, recommended that Hanekom apply BacTech’s Rescue prior to planting. “Rescue basically sterilises the soil and can’t be used along with other biological products. It is, however, very effective to help control pathogens in the soil early in the season.”
A NEW YEAR
In 2016, Hanekom treated his seed potatoes with Diathane (Reg. no. L2914) and applied Monceren (Reg. no. L3123) to the furrows. “During the first week after emergence, we applied 500 ml/ha of Rescue and between weeks 8 and 9 we applied 1 l/ha BacToLife and 1 l/ha ScleroStop. We noticed that rhizoctonia was getting a hold of the tubers again when we did routine inspections between weeks 12 and 13. So, we still had a loss in 2016, but it was less than 5% and I was convinced that we were on the right path.
“We decided to apply 500 ml/ha Rescue again in 2017 after treating the seed potatoes with Diathane and applying Momento (Reg. no. L7984) to the furrows. Between weeks 3 and 4 we applied 500 ml/ha each of BacTech’s Bactoviridis and Fungal-Go, and in week 8 we added 500 ml/ha each of BacToLife and ScleroStop. We’re going to start applying a further 500 ml/ha of both again in week 12 to keep the potatoes healthy until harvest.
“I dig around in our fields twice to three times per week and I haven’t detected any rhizoctonia. This programme gives me peace of mind that I’m protected against fungus for the entire season,” says Hanekom.
According to Meyer, this programme cost Hanekom R3 580/ha with an average yield of 50 ton/ha. If one assumes that Hanekom would have lost 10%, or 5 ton/ha, due to rhizoctonia, and that the average price of potatoes at the time was R3.50/kg, he lost R17 500/ha before he started using biological products.
For Hanekom, the 2015 season was the biggest lesson learned in recent times. “We didn’t follow the prescribed dosage instructions and we paid the price. My advice to other farmers is to apply the programme correctly. Even if you’re only testing it on a part of your plantings, ensure that you do the trial completely and effectively.”