Production, safe storage, trade and utilisation of grain remain a vital part of the world economy. Grain is th staple food in many countries, is extensively used in processed food and is an important ingredient in animal feeds. It therefore is important to both developed and developing economies.
The Stored Grain and Oilseed Unit is committed to the provision of high quality investigations, monitoring, research and technology transfer services to determine requirements and technical means of safe and insect-free small farm storage, medium storage and large scale storage of grain.
The Stored Grain and Oil Seed Research Unit does research and can be of assistance in the following activities:
Stored grain insect culture:
The origin of the insects of stored grain is not well known. Undoubtedly they lived in the fields in the seeds that escaped the attention of the birds. Humans began to cultivate plants around 8000 BC in the Middle East, the custom to store seeds for food, adopted by man during this time, provided an easy living for insects accidentally brought in with the seeds. Ideal conditions for breeding, provided by these stores, made it unnecessary for these insects to search for additional food. They adapted morphologically in size, colour and shape to go unnoticed in grain and be carried by grain handlers to all parts of the world. Supplies of grain placed in the tombs of ancient Egyptians were destroyed by the same species that we are familiar with today. The rust red flour beetle (Cryptolestis ferrugineus) was found in a tomb of a pharaoh dating back 1345 BC.
The stored Grain and Oilseed Research Unit has an insect culture consisting of 11 stored grain insect species commonly found in South Africa. PPRI – Stored Grain is currently the only organisation in South Africa specializing in stored grain insects. The University of Pretoria, University of Stellenbosch, the SABS, the CSIR and other PPRI divisions often use stored grain insects reared from this culture for their own trials. All the stored grain pesticide registration trials done by the unit make use of these insects to determine biological efficacy of the tested pesticides. Five phosphine susceptible insect species were especially imported from Canada and England to ensure phosphine resistant trials in South Africa. Currently the unit also has a field culture strain from the Cape Province to conduct contact pesticide resistance trials. The laboratory insect strain, which consist of the 11 species, is more than 20 years old. Three breeding rooms at specific temperatures are used to house these insect species. The rooms are calibrated on a three-year interval to ensure that the insects are kept at optimum breeding temperatures. Two adjacent smaller breeding rooms are used for the incubation of the insects during registration or pesticide resistant trials.
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Post-harvest constraints facing small-scale farmers and to improve post-harvest management strategies for improving household food security
The unit conducted studies in the Limpopo Province and North Region of KwaZulu-Natal, with the objective to improve household food security in rural South Africa, by analysing the post-harvest constraints and opportunities to rural livelihoods. A Participatory Rural Appraisal method was used to determine how pos-harvest constraints influence the livelihood strategies of rural households. The analysis of the questionnaire data revealed that the major post-harvest constraints remain consistently the same, irrespective of the crop. Damaged caused by insects or rodents in storage was always recorded as the most important constraint, followed by lack of transport of crop from field to home. Subsequent farmer participatory demonstration trials were conducted to train farmers and extension officers in grain storage hygiene and pest control.
The unit has conducted a number of stored grain pesticide registration trials for the grain industry/chemical companies. A trial usually consists of a pesticide treatment on a specific grain crop, biological efficacy trials. on the treated grain over a determined period of months, organoleptic tests, germination trials as well as residue analysis of the treated grain. After completion a final report is supplied to the client in where the performance of the pesticide is evaluated, the client can then continue with the registration of the product at the registrar. Recently completed trails include Super Guard as an EC and a dust formulation to control stored grain insect pests on maize, wheat and beans. The trial was conducted over a period of 12 months on three different grain types infested with five of the most commonly known stored grain insect pest species found in South Africa. The trial was concluded with very satisfying results by killing insect pests for the duration of the trial. The unit also completed the re-registration trial to extend the existing label of K-Obiol EC to be used as a surface spray as well as ‘n fog to kill all living insects. K-Obiol used as a fog killed all five insects species as well as moth eggs within 24 hours after “fumigation”. K-Obiol used as a surface spray remained very effective for the duration of the trial (4 months). Plant Protection Research Institute, Stored Grain and Oilseed Research Unit was also responsible for the original registration trials of K-Obiol in 1995.
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Evaluation of Phosphide fumigation products in South Africa
The success of any fumigation operation depends largely on the gas-tightness of the space to be fumigated. The gas must be retained for a minimum period of time to be effective against insects, a five to seven day exposure to an a effective concentration of phosphine to control most insect pests and their developmental stages. An early fall in the concentration of phosphine generally results in the failure of fumigation because the surviving insects rapidly rebuild their population in the absence of residual toxicant. Frequent exposures to sub-lethal levels of phosphine could also lead to the selection of resistant insects. Other factors contributing to the development of resistance are the use of inadequate amounts of phosphine and the movement of resistant insects as a result of grain trade. Since fumigants are gases, entry into an exposed insect is believed to be mainly through the respiratory system. The uptake of fumigant is generally proportional to the rate of respiration of the exposed insect. Factors, which increase respiratory activity, should also increase the uptake and toxicity of the fumigant. However the uptake of phosphine in insects essentially requires oxygen. Like other fumigants, toxicity of phosphine to insects increases with the rise in temperature within the normal range of ambient temperatures, probably due to the increase in metabolic rate and therefore an increase in oxygen consumption that will stimulate the uptake of phosphine. The pre-adult (eggs and pupae) stages are more tolerant to phosphine, due to the lower respiration compared to the adult stages. Tolerance to phosphine in eggs decrease with the age of the egg because of the elevation in metabolic rate and respiration as the egg continues to develop.
Generally, longer exposure of insects to phosphine, even at lower concentration, produces greater toxicity than shorter exposure to a high concentration. Increasing the concentration of phosphine may not necessarily produce greater efficacy, since several stored grain insects are capable of undergoing a state of “narcosis” and protects themselves from the toxic effects by lowering the respiration and metabolic activity, especially during short exposures.
To ensure a successful fumigation the standard of the product used is also very important, therefore the Grain Silo Industry decided in 2005 to annually test the phosphine products distributed in South Africa. The Grain Silo Industry (GSI) conducts a randomly selection of samples of the five distributors in South Africa, the SGO Unit then conducts qualitative and quantitative analyses to determine the phosphine yield, gas purity for each pellet/tablet/sachets as well as determine the mean weight and hardness of the pellets/tablets/sachets per sample. The unit makes use of the agreed upon method of United Phosphorus, India to determine the Aluminium phosphide content in the tested products. Currently the unit is the only organisation conducting these trials in South Africa.
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Rodent control research (Read more inside the final technical report Project R8190 and R8441 and Ratzooman)
Rodents are a long-standing problem throughout the world which disproportionately affect the rural poor through consuming and contaminating stored food, damaging field crops, transmitting diseases and degrading the built environment. It was therefore not surprising that a post-harvest needs assessment survey in four rural communities in the Limpopo Province conducted in 2001 and a similar survey in KwaZulu-Natal in 2004 identified rodent damage to stored grain as one of the major natural constraints. On the strength of these results a project was initiated in 2002 in the Limpopo Province and in 2005 extended to KwaZulu-Natal, with the objective to develop sustainable strategies for rodent management in rural communities of South Africa.
By working with target communities as well as the traditional rodent management service providers (Environmental Health Officers, Agricultural Extensionists, and the commercial pest control industry), the project developed methods and strategies that were researched and evaluated for their cost-benefits and ability to effectively deal with rodent pest problems as experienced by rural agricultural communities. This research was done in collaboration between Plant Protection Research Institute, Natural Resources Institute (UK) as well as the key stakeholders such as end users and service providers.
The activities were focussed on generating new knowledge with regard to understanding the impact of rodents on rural agricultural communities, trailing potential rodent management techniques, working with stakeholders to improve the relevance of rodent management services, and recommending policies that would help reduce long-term trends of increasing rodent pest problems. The research findings showed that rodents have multiple impacts on the livelihood of rural communities, which include biting people, damage to property, and damage to crops in fields and in storage. Although farmers had a general awareness about rodent control tools such as rodenticides and traps, knowledge on the correct and effective use thereof was lacking. To counter this, the foundation of a public-private service partnership was developed to promote rodent management knowledge and tools. In this partnership a series of training workshops for service providers were held in urban and rural centres. The attendance by local government’s environmental health and agricultural extension and the private sector is indicative that these sectors will take the acquired information further to their clients. These training workshops also initiated newly found co-operation between the sectors and can be seen as a major success of the project.
The management strategies tested were to reduce rodent populations through intensive trapping. Trap success from 10 break back traps per household in and around 80 households and 4 crop fields over a continues period of 18 months has demonstrated to the communities and government agricultural extension the effectiveness of trapping as a rodent control management tool, as well as the efficacy of the break back trap. However, using 10 traps per household is not cost effective. Subsequent adaptive research trials in KwaZulu-Natal demonstrated that efficient, sustainable cot effective rodent control can be achieved through the process of continuous trapping with two traps per household. These break back traps, initially imported from the USA, are user friendly and extremely sensitive and an improved version is now manufactured by a South African pest control company. This ensures cost stability and will add to the sustainability to rodent control management in rural communities. Severe drought conditions during the assessment period prevented reliable results of rodent damage to crops in storage. Damage to maize in crop field without trapping however ranged from 10% to 28%.
The dominant rodent species in households in the villages in the arid regions was the commensal house rat, while the indigenous multimammate-rat was the dominant rodent species in the village in the sub-tropical and mountainous region. The multimammate rat was also a dominant species in field crops of all the surveyed villages. Rodents were caught in all the localities in the households. While high numbers may be expected in localities where staple crops are stored, food is prepared or food waste is left, relatively high numbers were also caught in bedrooms. As both dominant species are medically important in the transmitting of rodent zoonosis, the close proximity between the carriers of diseases and human victims, especially children, is of great concern. Incidences of humans being bitten in their sleep and the wounds are left untreated, further confirms the case. Of scientific value was the discovery of the oriental rat Rattus tanezumi, a first recording of the species in Africa, which renewed scientific interest in research on commensal rodent species.
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Rodent Control Course
On request the Unit conducts a day course which includes a half day practical rodent control courses for Agricultural extension, environmental health and pest control operators.
Course content: Rodent biology and behaviour, rodent ecology, rodent control and monitoring.
Larger Grain Borer
Traditional small-scale maize growers include some of the poorest households in remote areas of South Africa. Maize production for small-scale farmers for the 1998/99 season was estimated at 394,100 tons, (average 0.7 tons per ha), of which some farmers experienced significantly annual losses during storage of 30% on average. In some cases, mainly due to poor storage facilities and lack of training, losses can be as high as 80%. In these cases, household food security is at great risk.
The appearance of the Larger Grain Borer (Prostephanus truncatus) during 1999 in the northern regions of the Limpopo Province further highlights the vulnerability of these farmers to crop losses. The Larger Grain Borer (LGB) is a serious pest of farm-stored maize and dried cassava in sub-Saharan Africa. It was introduced into Tanzania from meso-America in the late 1970s and has since spread widely, initially in East Africa and subsequently in West Africa. It is still spreading and is officially recorded from sixteen African countries; it reached South Africa in 1999 and is dispersing south-westerly towards the main maize production areas of South Africa.
The latest pheromone trap catches indicate that LGB has become established in the Vembe and Mopani districts of the Limpopo Province and in the North-eastern Mpumalanga bordering on the Kruger National Park. Resent verbal reports indicate that LGB is also present in Mozambique and in the northern regions of Namibia.
Where the pest is well established, it has been estimated that without appropriate pest management action, farm storage losses are doubled. Mortality assessments to determine pesticide efficacy Supplying farmer with trial pesticide On farm efficacy assessments with farmers Training of extension officers to dissect and identify rodents Rodents caught in traps during rodent trapping trial PPRI team together with the Lusikisiki farmers in front of the improved "drying hut" to decrease moisture in harvested grain and thereby eliminating fungal growth on stored maize. Unique storage structures (metal tanks) used by the Lusikisiki farmers for grain storage.
Programme Manager: Mr Frikkie Kirsten
Campus: Roodeplaat, Pretoria