By Charl van Rooyen
A new maize disease, Goss bacterial wilt and leaf blight, has hit the South African maize industry after it landed here from America. It has the potential to cause extensive in a maize field under ideal conditions, and it could potentially have an effect on exports.
In an international notification on Monday 14 January the International Plant Protection Convention (IPPC) of the Food and Agriculture Organization of the United Nations (FAO) officially confirmed that the disease, Clavibacter michiganensis subsp. nebraskensis (Goss’ wilt), is already present in four provinces in South Africa.
African Farming approached Dr Rikus Kloppers, a seasoned, independent specialist in crop diseases, for comment. He confirmed the disease has been reported on farms in several provinces. It was already observed in places last season, but due to its phytosanitary implications on the maize industry, the Department of Agriculture and Rural Development (DALRRD) (now the Department of Agriculture) first thoroughly investigated and positively identified it before it was officially announced.
Kloppers took his first steps in the maize industry at Pannar Seed about 30 years ago. Most of his career as a plant pathologist in the industry and later on a few years in international crop protection and seed treatment roles. He decided to come back to be more involved in the local agricultural industry again, and recently founded his own business, Robigalia CropCare. He currently does independent consultancy work in the local seed industry for, among others, local seed companies, and is also actively involved in the South African National Seed Organisation (SANSOR).
He says the symptoms are large white lesions on the leaves of the maize plants. “The dilemma is that it can easily be confused with northern maize leaf blight, drought stress and sunburn because the symptoms are very similar.” Identification through an accredited institution is therefore essential before acting on it.
The extent of infection varies from case to case, but according to literature, crop losses of up to 50% have been reported under ideal conditions – which usually include early infection with associated hail damage.
Stress accelerates the disease
Kloppers’ American counterparts in the industry, with many years’ experience in dealing with this disease, say Goss bacterial wilt and wilt leaf blight are accelerated by stress factors such as hail and wind damage. The Americans have been dealing with the disease for a very long time and manage it effectively with resistant maize cultivars and good agricultural practices, such as crop rotation and incorporation of infected residues into the soil for rapid breakdown.
Since it is a bacterial disease, fungicides are not effective and no other products that can control the disease have been registered. It is not yet known how or exactly when the disease spread to South Africa. The seed industry, national seed organisations, universities and other stakeholders are working closely with the Department of Agriculture to manage the risk of spread and to develop control measures to enable maize farmers to prevent and control the disease.
Kloppers says the disease could have phytosanitary implications for the import and export of maize to and from South Africa.
According to the IPPC publication, this disease is not yet widespread in South Africa and is “under official control”. After the NPPOZA (National Plant Protection Organisation of South Africa) was informed of signs of the disease, research institutes and the Department of Agriculture took samples from various farms in the Free State (Parys), North West (Fochville and Lichtenburg) and Gauteng (Carletonville) and tested them using molecular techniques. The occurrence of the disease has therefore been officially confirmed. It has also been found in Potchefstroom and has been visually observed in the Eastern Cape.
Investigations have been conducted in several other parts of the country, but the disease has not yet been confirmed there. According to the IPPC publication, phytosanitary measures are being applied on the affected farms.
There is a risk that the disease could spread from affected areas through host plants to other areas “and could harm local and international trade and export potential”. The Department of Agriculture is continuing its research to understand the epidemiology and management of the disease and to support local maize farmers while the investigation continues to determine exactly how widely it has already spread.
Comments from the Department of Agriculture will be added as soon as they are received.
