Nab the Scab: South African specialist’s views on how to deal with a nasty potato disease

Jacquie vanderWaalsPowdery scab of potatoes is a serious disease that is a thorn in the side of many a potato grower around the world. This is also the case in South Africa, one of the biggest potato producing countries on the African continent. In a recent article published on the website of the Afrikaans language agriculture magazine Landbou Weekblad, the views of a respected South African potato specialist on powdery scab are shared. Prof Jacquie van der Waals is Assistant Professor, Plant and Soil Sciences in the section Plant Pathology at the University of Pretoria. She says in an interview that powdery scab is indeed a disease that is very hard to control, and growers are advised to look not only at one possible solution to combat the problem, but use a range of integrated measurements at any one moment in time to deal with it. Jacquie is the founder and lead of the potato pathology project at the University of Pretoria and a seasoned potato researcher. She points to no less than 11 measures that potato growers can employ as part of an integrated control strategy to manage powdery scab. 

 One of these management tools is to employ a long rotation period of at least 5 years on land designated for potato production – a measurement that is valid for all soilborne diseases. Another is the choice of rotation crops. Jacquie points to some studies in New Zealand and Australia which showed that when Brassica crops, especially Caliente mustard, are planted in rotation with potatoes, the disease pressure is lower than when cereal crops are used in the rotation.

Detailed soil and seed testing: Jacquie says that it will pay off if growers do an effective PCR (Polymerase Chain Reaction) based test of their soils, even once a year for rotation fields – even though this kind of tests are somewhat more expensive, it will provide growers with a good idea of potential disease presence in the soil.

Well drained soils, seed that’s proven to be clean, and seed treatment before planting (although not a silver bullet) are other methods that growers should keep in mind when dealing with powdery scab.

In some cases it might be helpful if growers move their planting date a bit in order to avoid soil conditions that might be too cool during tuber initiation, since this kind of condition is favourable for powdery scab development at the tuber initiation phase of plant development. Jacquie also points out that over-irrigation during tuber initiation should be avoided.

Hygiene, hygiene, hygiene… Jacquie says that thorough cleaning of all equipment, storage facilities and mechanical equipment can not be overemphasized as a must in order to avoid contamination with spores.

One of the best methods is still to choose – if possible – a variety that is known to have a high tolerance against powdery scab, Jacquie says.

In summary: A thorough integrated strategy is advisable at all times. Use as many of the recommended control measures as practically possible, and do not rely on only one method as the only answer to the problem… Jacquie and her team at the University of Pretoria are involved in ongoing research to find novel solutions for the problem of powdery scab of potatoes in South Africa.

Jacquie Vanderwaals can be reached for further information at jacquie.vanderwaals@up.ac.za. Twitter: @jacquievdw

Credits: The orginal article was written in the Afrikaans language by Johann van der Merwe and can be found in the  in the print version of Landbou Weekblad and online on the Landbou.com website.