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Until flowering, the mass of plants from the fumigated plots significantly exceeded those from the other treatments, but thereafter the differences decreased. Root samples were analysed to determine the dominant pathogens.
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Root samples were collected from all plots during the season and grain yields were determined at harvest. Four treatments – control, methyl bromide fumigation and two biocides – were compared. The trials took place at Bergville and Winterton. “We also wanted to test the effects of two biocides, and assess the effects of soilborne diseases on nutrient uptake and the effect of soil fumigation and biocides on soil microbial diversity.” Trials were set up to identify the dominant soilborne pathogens in maize following winter wheat in no-till systems in the province, and to quantify the effects on growth and yield,” explains Dr Lamprecht. “Farmers in KZN expressed concern about soilborne diseases in maize planted after wheat. Tests have already shown that maize crop yields can be significantly increased after soil fumigation. Yield loss cannot be accurately estimated, because techniques are not available to compare yields of healthy and diseased corn plants.”ĭr Lamprecht said experiments are underway in South Africa, using soil fumigation as an experimental tool to determine yield losses caused by soilborne diseases. In 1999, the American agricultural scientist Dr Donald White said, “Root rots are among the least studied and least understood diseases of corn, even though they occur on every corn plant in every field, every year. Increased soil moisture levels, a result of this farming practice, favour the establishment and proliferation of pathogenic Pythium spp In the United States, it has been found that incidences of Rhizoctonia crown and brace root rot have increased because the soil under conservation tillage is only minimally disturbed. Maize crop residues routinely retained under conservation tillage provide an environment for soilborne pathogens such as Fusarium graminearum to survive until the next crop season. “While there is a considerable amount of information available on the effect of conservation tillage on ear and stalk rot of maize, information on this farming system’s effect on soilborne diseases of maize in South Africa is almost non-existent.” “Many pathogens increase to damaging levels under conservation tillage,” she explained.
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Speaking recently at an information day hosted by the KZN No-Till Club in Bergville, Dr Sandra Lamprecht, a plant pathologist at the ARC Plant Protection Research Institute in Stellenbosch, said that shifts in farming practices such as conservation tillage profoundly impact on plant pathogens. However, if the above-ground parts of our cereal crops were as damaged and diseased as the roots, there would be no end to support and efforts until the problems were solved.” Root diseases have become so widespread and occur so uniformly within fields that we have come to accept these crops as normal or healthy. Diseased root systems are unable to explore the soil for nutrients. In 2001, agricultural scientist Dr Jim Cook said, “If we can’t see these symptoms then we don’t know what damage they’re doing to the maize crop. A number of maize diseases commonly found in conservation tillage systems do not manifest on the visible plant structures above ground, yet ultimately have a severely negative effect on an enterprise’s profitability. Soilborne diseases are among the most important yield-limiting factors in crop production worldwide. The management of soilborne plant diseases is one of the greatestĬhallenges facing modern agriculture, as Lloyd Phillips discovered duringĪn information day of the KwaZulu-Natal No-Till Club in Bergville.